vendor: golang.org/x/text v0.31.0

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>
2025-11-27 19:12:17 +01:00
parent 3f5c571f69
commit ae3eed7b80
48 changed files with 2658 additions and 313 deletions
@@ -62,7 +62,7 @@ require (
 	golang.org/x/sync v0.18.0
 	golang.org/x/sys v0.38.0
 	golang.org/x/term v0.37.0
-	golang.org/x/text v0.29.0
+	golang.org/x/text v0.31.0
 	google.golang.org/genproto/googleapis/rpc v0.0.0-20250825161204-c5933d9347a5
 	google.golang.org/grpc v1.76.0
 	google.golang.org/grpc/cmd/protoc-gen-go-grpc v1.5.1
@@ -160,11 +160,11 @@ require (
 	go.opentelemetry.io/otel/sdk/metric v1.38.0 // indirect
 	go.opentelemetry.io/proto/otlp v1.7.1 // indirect
 	go.yaml.in/yaml/v2 v2.4.2 // indirect
-	golang.org/x/crypto v0.42.0 // indirect
-	golang.org/x/net v0.44.0 // indirect
+	golang.org/x/crypto v0.43.0 // indirect
+	golang.org/x/net v0.46.0 // indirect
 	golang.org/x/oauth2 v0.30.0 // indirect
 	golang.org/x/time v0.14.0 // indirect
-	golang.org/x/tools v0.37.0 // indirect
+	golang.org/x/tools v0.38.0 // indirect
 	google.golang.org/genproto/googleapis/api v0.0.0-20250825161204-c5933d9347a5 // indirect
 	gopkg.in/evanphx/json-patch.v4 v4.12.0 // indirect
 	gopkg.in/inf.v0 v0.9.1 // indirect
@@ -382,8 +382,8 @@ go.yaml.in/yaml/v3 v3.0.4/go.mod h1:DhzuOOF2ATzADvBadXxruRBLzYTpT36CKvDb3+aBEFg=
 golang.org/x/crypto v0.0.0-20190308221718-c2843e01d9a2/go.mod h1:djNgcEr1/C05ACkg1iLfiJU5Ep61QUkGW8qpdssI0+w=
 golang.org/x/crypto v0.0.0-20191011191535-87dc89f01550/go.mod h1:yigFU9vqHzYiE8UmvKecakEJjdnWj3jj499lnFckfCI=
 golang.org/x/crypto v0.0.0-20200622213623-75b288015ac9/go.mod h1:LzIPMQfyMNhhGPhUkYOs5KpL4U8rLKemX1yGLhDgUto=
-golang.org/x/crypto v0.42.0 h1:chiH31gIWm57EkTXpwnqf8qeuMUi0yekh6mT2AvFlqI=
-golang.org/x/crypto v0.42.0/go.mod h1:4+rDnOTJhQCx2q7/j6rAN5XDw8kPjeaXEUR2eL94ix8=
+golang.org/x/crypto v0.43.0 h1:dduJYIi3A3KOfdGOHX8AVZ/jGiyPa3IbBozJ5kNuE04=
+golang.org/x/crypto v0.43.0/go.mod h1:BFbav4mRNlXJL4wNeejLpWxB7wMbc79PdRGhWKncxR0=
 golang.org/x/mod v0.2.0/go.mod h1:s0Qsj1ACt9ePp/hMypM3fl4fZqREWJwdYDEqhRiZZUA=
 golang.org/x/mod v0.3.0/go.mod h1:s0Qsj1ACt9ePp/hMypM3fl4fZqREWJwdYDEqhRiZZUA=
 golang.org/x/mod v0.29.0 h1:HV8lRxZC4l2cr3Zq1LvtOsi/ThTgWnUk/y64QSs8GwA=
@@ -392,8 +392,8 @@ golang.org/x/net v0.0.0-20190404232315-eb5bcb51f2a3/go.mod h1:t9HGtf8HONx5eT2rtn
 golang.org/x/net v0.0.0-20190620200207-3b0461eec859/go.mod h1:z5CRVTTTmAJ677TzLLGU+0bjPO0LkuOLi4/5GtJWs/s=
 golang.org/x/net v0.0.0-20200226121028-0de0cce0169b/go.mod h1:z5CRVTTTmAJ677TzLLGU+0bjPO0LkuOLi4/5GtJWs/s=
 golang.org/x/net v0.0.0-20201021035429-f5854403a974/go.mod h1:sp8m0HH+o8qH0wwXwYZr8TS3Oi6o0r6Gce1SSxlDquU=
-golang.org/x/net v0.44.0 h1:evd8IRDyfNBMBTTY5XRF1vaZlD+EmWx6x8PkhR04H/I=
-golang.org/x/net v0.44.0/go.mod h1:ECOoLqd5U3Lhyeyo/QDCEVQ4sNgYsqvCZ722XogGieY=
+golang.org/x/net v0.46.0 h1:giFlY12I07fugqwPuWJi68oOnpfqFnJIJzaIIm2JVV4=
+golang.org/x/net v0.46.0/go.mod h1:Q9BGdFy1y4nkUwiLvT5qtyhAnEHgnQ/zd8PfU6nc210=
 golang.org/x/oauth2 v0.30.0 h1:dnDm7JmhM45NNpd8FDDeLhK6FwqbOf4MLCM9zb1BOHI=
 golang.org/x/oauth2 v0.30.0/go.mod h1:B++QgG3ZKulg6sRPGD/mqlHQs5rB3Ml9erfeDY7xKlU=
 golang.org/x/sync v0.0.0-20190423024810-112230192c58/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
@@ -413,16 +413,16 @@ golang.org/x/term v0.37.0 h1:8EGAD0qCmHYZg6J17DvsMy9/wJ7/D/4pV/wfnld5lTU=
 golang.org/x/term v0.37.0/go.mod h1:5pB4lxRNYYVZuTLmy8oR2BH8dflOR+IbTYFD8fi3254=
 golang.org/x/text v0.3.0/go.mod h1:NqM8EUOU14njkJ3fqMW+pc6Ldnwhi/IjpwHt7yyuwOQ=
 golang.org/x/text v0.3.3/go.mod h1:5Zoc/QRtKVWzQhOtBMvqHzDpF6irO9z98xDceosuGiQ=
-golang.org/x/text v0.29.0 h1:1neNs90w9YzJ9BocxfsQNHKuAT4pkghyXc4nhZ6sJvk=
-golang.org/x/text v0.29.0/go.mod h1:7MhJOA9CD2qZyOKYazxdYMF85OwPdEr9jTtBpO7ydH4=
+golang.org/x/text v0.31.0 h1:aC8ghyu4JhP8VojJ2lEHBnochRno1sgL6nEi9WGFGMM=
+golang.org/x/text v0.31.0/go.mod h1:tKRAlv61yKIjGGHX/4tP1LTbc13YSec1pxVEWXzfoeM=
 golang.org/x/time v0.14.0 h1:MRx4UaLrDotUKUdCIqzPC48t1Y9hANFKIRpNx+Te8PI=
 golang.org/x/time v0.14.0/go.mod h1:eL/Oa2bBBK0TkX57Fyni+NgnyQQN4LitPmob2Hjnqw4=
 golang.org/x/tools v0.0.0-20180917221912-90fa682c2a6e/go.mod h1:n7NCudcB/nEzxVGmLbDWY5pfWTLqBcC2KZ6jyYvM4mQ=
 golang.org/x/tools v0.0.0-20191119224855-298f0cb1881e/go.mod h1:b+2E5dAYhXwXZwtnZ6UAqBI28+e2cm9otk0dWdXHAEo=
 golang.org/x/tools v0.0.0-20200619180055-7c47624df98f/go.mod h1:EkVYQZoAsY45+roYkvgYkIh4xh/qjgUK9TdY2XT94GE=
 golang.org/x/tools v0.0.0-20210106214847-113979e3529a/go.mod h1:emZCQorbCU4vsT4fOWvOPXz4eW1wZW4PmDk9uLelYpA=
-golang.org/x/tools v0.37.0 h1:DVSRzp7FwePZW356yEAChSdNcQo6Nsp+fex1SUW09lE=
-golang.org/x/tools v0.37.0/go.mod h1:MBN5QPQtLMHVdvsbtarmTNukZDdgwdwlO5qGacAzF0w=
+golang.org/x/tools v0.38.0 h1:Hx2Xv8hISq8Lm16jvBZ2VQf+RLmbd7wVUsALibYI/IQ=
+golang.org/x/tools v0.38.0/go.mod h1:yEsQ/d/YK8cjh0L6rZlY8tgtlKiBNTL14pGDJPJpYQs=
 golang.org/x/xerrors v0.0.0-20190717185122-a985d3407aa7/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=
 golang.org/x/xerrors v0.0.0-20191011141410-1b5146add898/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=
 golang.org/x/xerrors v0.0.0-20191204190536-9bdfabe68543/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=
@@ -3,11 +3,14 @@
 // license that can be found in the LICENSE file.

 // Package curve25519 provides an implementation of the X25519 function, which
-// performs scalar multiplication on the elliptic curve known as Curve25519.
-// See RFC 7748.
+// performs scalar multiplication on the elliptic curve known as Curve25519
+// according to [RFC 7748].
 //
-// This package is a wrapper for the X25519 implementation
-// in the crypto/ecdh package.
+// The curve25519 package is a wrapper for the X25519 implementation in the
+// crypto/ecdh package. It is [frozen] and is not accepting new features.
+//
+// [RFC 7748]: https://datatracker.ietf.org/doc/html/rfc7748
+// [frozen]: https://go.dev/wiki/Frozen
 package curve25519

 import "crypto/ecdh"
@@ -4,20 +4,15 @@

 // Package sign signs small messages using public-key cryptography.
 //
-// Sign uses Ed25519 to sign messages. The length of messages is not hidden.
-// Messages should be small because:
-// 1. The whole message needs to be held in memory to be processed.
-// 2. Using large messages pressures implementations on small machines to process
-// plaintext without verifying the signature. This is very dangerous, and this API
-// discourages it, but a protocol that uses excessive message sizes might present
-// some implementations with no other choice.
-// 3. Performance may be improved by working with messages that fit into data caches.
-// Thus large amounts of data should be chunked so that each message is small.
+// This package is interoperable with [libsodium], as well as [TweetNaCl].
 //
-// This package is not interoperable with the current release of NaCl
-// (https://nacl.cr.yp.to/sign.html), which does not support Ed25519 yet. However,
-// it is compatible with the NaCl fork libsodium (https://www.libsodium.org), as well
-// as TweetNaCl (https://tweetnacl.cr.yp.to/).
+// The sign package is essentially a wrapper for the Ed25519 signature
+// algorithm (implemented by crypto/ed25519). It is [frozen] and is not accepting
+// new features.
+//
+// [libsodium]: https://libsodium.gitbook.io/doc/public-key_cryptography/public-key_signatures
+// [TweetNaCl]: https://tweetnacl.cr.yp.to/
+// [frozen]: https://go.dev/wiki/Frozen
 package sign

 import (
@@ -430,8 +430,9 @@ func (c *client) List() ([]*Key, error) {
 		return keys, nil
 	case *failureAgentMsg:
 		return nil, errors.New("agent: failed to list keys")
+	default:
+		return nil, fmt.Errorf("agent: failed to list keys, unexpected message type %T", msg)
 	}
-	panic("unreachable")
 }

 // Sign has the agent sign the data using a protocol 2 key as defined
@@ -462,8 +463,9 @@ func (c *client) SignWithFlags(key ssh.PublicKey, data []byte, flags SignatureFl
 		return &sig, nil
 	case *failureAgentMsg:
 		return nil, errors.New("agent: failed to sign challenge")
+	default:
+		return nil, fmt.Errorf("agent: failed to sign challenge, unexpected message type %T", msg)
 	}
-	panic("unreachable")
 }

 // unmarshal parses an agent message in packet, returning the parsed
@@ -8,6 +8,7 @@ import (
 	"crypto/aes"
 	"crypto/cipher"
 	"crypto/des"
+	"crypto/fips140"
 	"crypto/rc4"
 	"crypto/subtle"
 	"encoding/binary"
@@ -15,6 +16,7 @@ import (
 	"fmt"
 	"hash"
 	"io"
+	"slices"

 	"golang.org/x/crypto/chacha20"
 	"golang.org/x/crypto/internal/poly1305"
@@ -93,41 +95,41 @@ func streamCipherMode(skip int, createFunc func(key, iv []byte) (cipher.Stream,
 }

 // cipherModes documents properties of supported ciphers. Ciphers not included
-// are not supported and will not be negotiated, even if explicitly requested in
-// ClientConfig.Crypto.Ciphers.
-var cipherModes = map[string]*cipherMode{
-	// Ciphers from RFC 4344, which introduced many CTR-based ciphers. Algorithms
-	// are defined in the order specified in the RFC.
-	CipherAES128CTR: {16, aes.BlockSize, streamCipherMode(0, newAESCTR)},
-	CipherAES192CTR: {24, aes.BlockSize, streamCipherMode(0, newAESCTR)},
-	CipherAES256CTR: {32, aes.BlockSize, streamCipherMode(0, newAESCTR)},
+// are not supported and will not be negotiated, even if explicitly configured.
+// When FIPS mode is enabled, only FIPS-approved algorithms are included.
+var cipherModes = map[string]*cipherMode{}

-	// Ciphers from RFC 4345, which introduces security-improved arcfour ciphers.
-	// They are defined in the order specified in the RFC.
-	InsecureCipherRC4128: {16, 0, streamCipherMode(1536, newRC4)},
-	InsecureCipherRC4256: {32, 0, streamCipherMode(1536, newRC4)},
+func init() {
+	cipherModes[CipherAES128CTR] = &cipherMode{16, aes.BlockSize, streamCipherMode(0, newAESCTR)}
+	cipherModes[CipherAES192CTR] = &cipherMode{24, aes.BlockSize, streamCipherMode(0, newAESCTR)}
+	cipherModes[CipherAES256CTR] = &cipherMode{32, aes.BlockSize, streamCipherMode(0, newAESCTR)}
+	//  Use of GCM with arbitrary IVs is not allowed in FIPS 140-only mode,
+	// we'll wire it up to NewGCMForSSH in Go 1.26.
+	//
+	// For now it means we'll work with fips140=on but not fips140=only.
+	cipherModes[CipherAES128GCM] = &cipherMode{16, 12, newGCMCipher}
+	cipherModes[CipherAES256GCM] = &cipherMode{32, 12, newGCMCipher}

-	// Cipher defined in RFC 4253, which describes SSH Transport Layer Protocol.
-	// Note that this cipher is not safe, as stated in RFC 4253: "Arcfour (and
-	// RC4) has problems with weak keys, and should be used with caution."
-	// RFC 4345 introduces improved versions of Arcfour.
-	InsecureCipherRC4: {16, 0, streamCipherMode(0, newRC4)},
-
-	// AEAD ciphers
-	CipherAES128GCM:        {16, 12, newGCMCipher},
-	CipherAES256GCM:        {32, 12, newGCMCipher},
-	CipherChaCha20Poly1305: {64, 0, newChaCha20Cipher},
+	if fips140.Enabled() {
+		defaultCiphers = slices.DeleteFunc(defaultCiphers, func(algo string) bool {
+			_, ok := cipherModes[algo]
+			return !ok
+		})
+		return
+	}

+	cipherModes[CipherChaCha20Poly1305] = &cipherMode{64, 0, newChaCha20Cipher}
+	// Insecure ciphers not included in the default configuration.
+	cipherModes[InsecureCipherRC4128] = &cipherMode{16, 0, streamCipherMode(1536, newRC4)}
+	cipherModes[InsecureCipherRC4256] = &cipherMode{32, 0, streamCipherMode(1536, newRC4)}
+	cipherModes[InsecureCipherRC4] = &cipherMode{16, 0, streamCipherMode(0, newRC4)}
 	// CBC mode is insecure and so is not included in the default config.
 	// (See https://www.ieee-security.org/TC/SP2013/papers/4977a526.pdf). If absolutely
 	// needed, it's possible to specify a custom Config to enable it.
 	// You should expect that an active attacker can recover plaintext if
 	// you do.
-	InsecureCipherAES128CBC: {16, aes.BlockSize, newAESCBCCipher},
-
-	// 3des-cbc is insecure and is not included in the default
-	// config.
-	InsecureCipherTripleDESCBC: {24, des.BlockSize, newTripleDESCBCCipher},
+	cipherModes[InsecureCipherAES128CBC] = &cipherMode{16, aes.BlockSize, newAESCBCCipher}
+	cipherModes[InsecureCipherTripleDESCBC] = &cipherMode{24, des.BlockSize, newTripleDESCBCCipher}
 }

 // prefixLen is the length of the packet prefix that contains the packet length
@@ -9,6 +9,7 @@ import (
 	"errors"
 	"fmt"
 	"io"
+	"slices"
 	"strings"
 )

@@ -83,7 +84,7 @@ func (c *connection) clientAuthenticate(config *ClientConfig) error {
 			// success
 			return nil
 		} else if ok == authFailure {
-			if m := auth.method(); !contains(tried, m) {
+			if m := auth.method(); !slices.Contains(tried, m) {
 				tried = append(tried, m)
 			}
 		}
@@ -97,7 +98,7 @@ func (c *connection) clientAuthenticate(config *ClientConfig) error {
 	findNext:
 		for _, a := range config.Auth {
 			candidateMethod := a.method()
-			if contains(tried, candidateMethod) {
+			if slices.Contains(tried, candidateMethod) {
 				continue
 			}
 			for _, meth := range methods {
@@ -117,15 +118,6 @@ func (c *connection) clientAuthenticate(config *ClientConfig) error {
 	return fmt.Errorf("ssh: unable to authenticate, attempted methods %v, no supported methods remain", tried)
 }

-func contains(list []string, e string) bool {
-	for _, s := range list {
-		if s == e {
-			return true
-		}
-	}
-	return false
-}
-
 // An AuthMethod represents an instance of an RFC 4252 authentication method.
 type AuthMethod interface {
 	// auth authenticates user over transport t.
@@ -255,7 +247,7 @@ func pickSignatureAlgorithm(signer Signer, extensions map[string][]byte) (MultiA
 		// Fallback to use if there is no "server-sig-algs" extension or a
 		// common algorithm cannot be found. We use the public key format if the
 		// MultiAlgorithmSigner supports it, otherwise we return an error.
-		if !contains(as.Algorithms(), underlyingAlgo(keyFormat)) {
+		if !slices.Contains(as.Algorithms(), underlyingAlgo(keyFormat)) {
 			return "", fmt.Errorf("ssh: no common public key signature algorithm, server only supports %q for key type %q, signer only supports %v",
 				underlyingAlgo(keyFormat), keyFormat, as.Algorithms())
 		}
@@ -284,7 +276,7 @@ func pickSignatureAlgorithm(signer Signer, extensions map[string][]byte) (MultiA
 	// Filter algorithms based on those supported by MultiAlgorithmSigner.
 	var keyAlgos []string
 	for _, algo := range algorithmsForKeyFormat(keyFormat) {
-		if contains(as.Algorithms(), underlyingAlgo(algo)) {
+		if slices.Contains(as.Algorithms(), underlyingAlgo(algo)) {
 			keyAlgos = append(keyAlgos, algo)
 		}
 	}
@@ -334,7 +326,7 @@ func (cb publicKeyCallback) auth(session []byte, user string, c packetConn, rand
 		// the key try to use the obtained algorithm as if "server-sig-algs" had
 		// not been implemented if supported from the algorithm signer.
 		if !ok && idx < origSignersLen && isRSACert(algo) && algo != CertAlgoRSAv01 {
-			if contains(as.Algorithms(), KeyAlgoRSA) {
+			if slices.Contains(as.Algorithms(), KeyAlgoRSA) {
 				// We retry using the compat algorithm after all signers have
 				// been tried normally.
 				signers = append(signers, &multiAlgorithmSigner{
@@ -385,7 +377,7 @@ func (cb publicKeyCallback) auth(session []byte, user string, c packetConn, rand
 		// contain the "publickey" method, do not attempt to authenticate with any
 		// other keys.  According to RFC 4252 Section 7, the latter can occur when
 		// additional authentication methods are required.
-		if success == authSuccess || !contains(methods, cb.method()) {
+		if success == authSuccess || !slices.Contains(methods, cb.method()) {
 			return success, methods, err
 		}
 	}
@@ -434,7 +426,7 @@ func confirmKeyAck(key PublicKey, c packetConn) (bool, error) {
 			// servers send the key type instead. OpenSSH allows any algorithm
 			// that matches the public key, so we do the same.
 			// https://github.com/openssh/openssh-portable/blob/86bdd385/sshconnect2.c#L709
-			if !contains(algorithmsForKeyFormat(key.Type()), msg.Algo) {
+			if !slices.Contains(algorithmsForKeyFormat(key.Type()), msg.Algo) {
 				return false, nil
 			}
 			if !bytes.Equal(msg.PubKey, pubKey) {
@@ -6,6 +6,7 @@ package ssh

 import (
 	"crypto"
+	"crypto/fips140"
 	"crypto/rand"
 	"fmt"
 	"io"
@@ -256,6 +257,40 @@ type Algorithms struct {
 	PublicKeyAuths []string
 }

+func init() {
+	if fips140.Enabled() {
+		defaultHostKeyAlgos = slices.DeleteFunc(defaultHostKeyAlgos, func(algo string) bool {
+			_, err := hashFunc(underlyingAlgo(algo))
+			return err != nil
+		})
+		defaultPubKeyAuthAlgos = slices.DeleteFunc(defaultPubKeyAuthAlgos, func(algo string) bool {
+			_, err := hashFunc(underlyingAlgo(algo))
+			return err != nil
+		})
+	}
+}
+
+func hashFunc(format string) (crypto.Hash, error) {
+	switch format {
+	case KeyAlgoRSASHA256, KeyAlgoECDSA256, KeyAlgoSKED25519, KeyAlgoSKECDSA256:
+		return crypto.SHA256, nil
+	case KeyAlgoECDSA384:
+		return crypto.SHA384, nil
+	case KeyAlgoRSASHA512, KeyAlgoECDSA521:
+		return crypto.SHA512, nil
+	case KeyAlgoED25519:
+		// KeyAlgoED25519 doesn't pre-hash.
+		return 0, nil
+	case KeyAlgoRSA, InsecureKeyAlgoDSA:
+		if fips140.Enabled() {
+			return 0, fmt.Errorf("ssh: hash algorithm for format %q not allowed in FIPS 140 mode", format)
+		}
+		return crypto.SHA1, nil
+	default:
+		return 0, fmt.Errorf("ssh: hash algorithm for format %q not mapped", format)
+	}
+}
+
 // SupportedAlgorithms returns algorithms currently implemented by this package,
 // excluding those with security issues, which are returned by
 // InsecureAlgorithms. The algorithms listed here are in preference order.
@@ -283,21 +318,6 @@ func InsecureAlgorithms() Algorithms {

 var supportedCompressions = []string{compressionNone}

-// hashFuncs keeps the mapping of supported signature algorithms to their
-// respective hashes needed for signing and verification.
-var hashFuncs = map[string]crypto.Hash{
-	KeyAlgoRSA:         crypto.SHA1,
-	KeyAlgoRSASHA256:   crypto.SHA256,
-	KeyAlgoRSASHA512:   crypto.SHA512,
-	InsecureKeyAlgoDSA: crypto.SHA1,
-	KeyAlgoECDSA256:    crypto.SHA256,
-	KeyAlgoECDSA384:    crypto.SHA384,
-	KeyAlgoECDSA521:    crypto.SHA512,
-	// KeyAlgoED25519 doesn't pre-hash.
-	KeyAlgoSKECDSA256: crypto.SHA256,
-	KeyAlgoSKED25519:  crypto.SHA256,
-}
-
 // algorithmsForKeyFormat returns the supported signature algorithms for a given
 // public key format (PublicKey.Type), in order of preference. See RFC 8332,
 // Section 2. See also the note in sendKexInit on backwards compatibility.
@@ -312,11 +332,40 @@ func algorithmsForKeyFormat(keyFormat string) []string {
 	}
 }

+// keyFormatForAlgorithm returns the key format corresponding to the given
+// signature algorithm. It returns an empty string if the signature algorithm is
+// invalid or unsupported.
+func keyFormatForAlgorithm(sigAlgo string) string {
+	switch sigAlgo {
+	case KeyAlgoRSA, KeyAlgoRSASHA256, KeyAlgoRSASHA512:
+		return KeyAlgoRSA
+	case CertAlgoRSAv01, CertAlgoRSASHA256v01, CertAlgoRSASHA512v01:
+		return CertAlgoRSAv01
+	case KeyAlgoED25519,
+		KeyAlgoSKED25519,
+		KeyAlgoSKECDSA256,
+		KeyAlgoECDSA256,
+		KeyAlgoECDSA384,
+		KeyAlgoECDSA521,
+		InsecureKeyAlgoDSA,
+		InsecureCertAlgoDSAv01,
+		CertAlgoECDSA256v01,
+		CertAlgoECDSA384v01,
+		CertAlgoECDSA521v01,
+		CertAlgoSKECDSA256v01,
+		CertAlgoED25519v01,
+		CertAlgoSKED25519v01:
+		return sigAlgo
+	default:
+		return ""
+	}
+}
+
 // isRSA returns whether algo is a supported RSA algorithm, including certificate
 // algorithms.
 func isRSA(algo string) bool {
 	algos := algorithmsForKeyFormat(KeyAlgoRSA)
-	return contains(algos, underlyingAlgo(algo))
+	return slices.Contains(algos, underlyingAlgo(algo))
 }

 func isRSACert(algo string) bool {
@@ -515,7 +564,7 @@ func (c *Config) SetDefaults() {
 		if kexAlgoMap[k] != nil {
 			// Ignore the KEX if we have no kexAlgoMap definition.
 			kexs = append(kexs, k)
-			if k == KeyExchangeCurve25519 && !contains(c.KeyExchanges, keyExchangeCurve25519LibSSH) {
+			if k == KeyExchangeCurve25519 && !slices.Contains(c.KeyExchanges, keyExchangeCurve25519LibSSH) {
 				kexs = append(kexs, keyExchangeCurve25519LibSSH)
 			}
 		}
@@ -17,8 +17,18 @@ References:
 	[PROTOCOL.certkeys]: http://cvsweb.openbsd.org/cgi-bin/cvsweb/src/usr.bin/ssh/PROTOCOL.certkeys?rev=HEAD
 	[SSH-PARAMETERS]:    http://www.iana.org/assignments/ssh-parameters/ssh-parameters.xml#ssh-parameters-1
 	[SSH-CERTS]:	https://datatracker.ietf.org/doc/html/draft-miller-ssh-cert-01
+	[FIPS 140-3 mode]: https://go.dev/doc/security/fips140

 This package does not fall under the stability promise of the Go language itself,
 so its API may be changed when pressing needs arise.
+
+# FIPS 140-3 mode
+
+When the program is in [FIPS 140-3 mode], this package behaves as if only SP
+800-140C and SP 800-140D approved cipher suites, signature algorithms,
+certificate public key types and sizes, and key exchange and derivation
+algorithms were implemented. Others are silently ignored and not negotiated, or
+rejected. This set may depend on the algorithms supported by the FIPS 140-3 Go
+Cryptographic Module selected with GOFIPS140, and may change across Go versions.
 */
 package ssh
@@ -10,6 +10,7 @@ import (
 	"io"
 	"log"
 	"net"
+	"slices"
 	"strings"
 	"sync"
 )
@@ -527,7 +528,7 @@ func (t *handshakeTransport) sendKexInit() error {
 			switch s := k.(type) {
 			case MultiAlgorithmSigner:
 				for _, algo := range algorithmsForKeyFormat(keyFormat) {
-					if contains(s.Algorithms(), underlyingAlgo(algo)) {
+					if slices.Contains(s.Algorithms(), underlyingAlgo(algo)) {
 						msg.ServerHostKeyAlgos = append(msg.ServerHostKeyAlgos, algo)
 					}
 				}
@@ -679,7 +680,7 @@ func (t *handshakeTransport) enterKeyExchange(otherInitPacket []byte) error {
 		return err
 	}

-	if t.sessionID == nil && ((isClient && contains(serverInit.KexAlgos, kexStrictServer)) || (!isClient && contains(clientInit.KexAlgos, kexStrictClient))) {
+	if t.sessionID == nil && ((isClient && slices.Contains(serverInit.KexAlgos, kexStrictServer)) || (!isClient && slices.Contains(clientInit.KexAlgos, kexStrictClient))) {
 		t.strictMode = true
 		if err := t.conn.setStrictMode(); err != nil {
 			return err
@@ -736,7 +737,7 @@ func (t *handshakeTransport) enterKeyExchange(otherInitPacket []byte) error {
 	// On the server side, after the first SSH_MSG_NEWKEYS, send a SSH_MSG_EXT_INFO
 	// message with the server-sig-algs extension if the client supports it. See
 	// RFC 8308, Sections 2.4 and 3.1, and [PROTOCOL], Section 1.9.
-	if !isClient && firstKeyExchange && contains(clientInit.KexAlgos, "ext-info-c") {
+	if !isClient && firstKeyExchange && slices.Contains(clientInit.KexAlgos, "ext-info-c") {
 		supportedPubKeyAuthAlgosList := strings.Join(t.publicKeyAuthAlgorithms, ",")
 		extInfo := &extInfoMsg{
 			NumExtensions: 2,
@@ -790,7 +791,7 @@ func (a algorithmSignerWrapper) SignWithAlgorithm(rand io.Reader, data []byte, a
 func pickHostKey(hostKeys []Signer, algo string) AlgorithmSigner {
 	for _, k := range hostKeys {
 		if s, ok := k.(MultiAlgorithmSigner); ok {
-			if !contains(s.Algorithms(), underlyingAlgo(algo)) {
+			if !slices.Contains(s.Algorithms(), underlyingAlgo(algo)) {
 				continue
 			}
 		}
@@ -8,12 +8,14 @@ import (
 	"crypto"
 	"crypto/ecdsa"
 	"crypto/elliptic"
+	"crypto/fips140"
 	"crypto/rand"
 	"encoding/binary"
 	"errors"
 	"fmt"
 	"io"
 	"math/big"
+	"slices"

 	"golang.org/x/crypto/curve25519"
 )
@@ -395,9 +397,27 @@ func ecHash(curve elliptic.Curve) crypto.Hash {
 	return crypto.SHA512
 }

+// kexAlgoMap defines the supported KEXs. KEXs not included are not supported
+// and will not be negotiated, even if explicitly configured. When FIPS mode is
+// enabled, only FIPS-approved algorithms are included.
 var kexAlgoMap = map[string]kexAlgorithm{}

 func init() {
+	// mlkem768x25519-sha256 we'll work with fips140=on but not fips140=only
+	// until Go 1.26.
+	kexAlgoMap[KeyExchangeMLKEM768X25519] = &mlkem768WithCurve25519sha256{}
+	kexAlgoMap[KeyExchangeECDHP521] = &ecdh{elliptic.P521()}
+	kexAlgoMap[KeyExchangeECDHP384] = &ecdh{elliptic.P384()}
+	kexAlgoMap[KeyExchangeECDHP256] = &ecdh{elliptic.P256()}
+
+	if fips140.Enabled() {
+		defaultKexAlgos = slices.DeleteFunc(defaultKexAlgos, func(algo string) bool {
+			_, ok := kexAlgoMap[algo]
+			return !ok
+		})
+		return
+	}
+
 	p, _ := new(big.Int).SetString(oakleyGroup2, 16)
 	kexAlgoMap[InsecureKeyExchangeDH1SHA1] = &dhGroup{
 		g:        new(big.Int).SetInt64(2),
@@ -431,14 +451,10 @@ func init() {
 		hashFunc: crypto.SHA512,
 	}

-	kexAlgoMap[KeyExchangeECDHP521] = &ecdh{elliptic.P521()}
-	kexAlgoMap[KeyExchangeECDHP384] = &ecdh{elliptic.P384()}
-	kexAlgoMap[KeyExchangeECDHP256] = &ecdh{elliptic.P256()}
 	kexAlgoMap[KeyExchangeCurve25519] = &curve25519sha256{}
 	kexAlgoMap[keyExchangeCurve25519LibSSH] = &curve25519sha256{}
 	kexAlgoMap[InsecureKeyExchangeDHGEXSHA1] = &dhGEXSHA{hashFunc: crypto.SHA1}
 	kexAlgoMap[KeyExchangeDHGEXSHA256] = &dhGEXSHA{hashFunc: crypto.SHA256}
-	kexAlgoMap[KeyExchangeMLKEM768X25519] = &mlkem768WithCurve25519sha256{}
 }

 // curve25519sha256 implements the curve25519-sha256 (formerly known as
@@ -27,6 +27,7 @@ import (
 	"fmt"
 	"io"
 	"math/big"
+	"slices"
 	"strings"

 	"golang.org/x/crypto/ssh/internal/bcrypt_pbkdf"
@@ -89,6 +90,11 @@ func parsePubKey(in []byte, algo string) (pubKey PublicKey, rest []byte, err err
 		}
 		return cert, nil, nil
 	}
+	if keyFormat := keyFormatForAlgorithm(algo); keyFormat != "" {
+		return nil, nil, fmt.Errorf("ssh: signature algorithm %q isn't a key format; key is malformed and should be re-encoded with type %q",
+			algo, keyFormat)
+	}
+
 	return nil, nil, fmt.Errorf("ssh: unknown key algorithm: %v", algo)
 }

@@ -191,9 +197,10 @@ func ParseKnownHosts(in []byte) (marker string, hosts []string, pubKey PublicKey
 	return "", nil, nil, "", nil, io.EOF
 }

-// ParseAuthorizedKey parses a public key from an authorized_keys
-// file used in OpenSSH according to the sshd(8) manual page.
+// ParseAuthorizedKey parses a public key from an authorized_keys file used in
+// OpenSSH according to the sshd(8) manual page. Invalid lines are ignored.
 func ParseAuthorizedKey(in []byte) (out PublicKey, comment string, options []string, rest []byte, err error) {
+	var lastErr error
 	for len(in) > 0 {
 		end := bytes.IndexByte(in, '\n')
 		if end != -1 {
@@ -222,6 +229,8 @@ func ParseAuthorizedKey(in []byte) (out PublicKey, comment string, options []str

 		if out, comment, err = parseAuthorizedKey(in[i:]); err == nil {
 			return out, comment, options, rest, nil
+		} else {
+			lastErr = err
 		}

 		// No key type recognised. Maybe there's an options field at
@@ -264,12 +273,18 @@ func ParseAuthorizedKey(in []byte) (out PublicKey, comment string, options []str
 		if out, comment, err = parseAuthorizedKey(in[i:]); err == nil {
 			options = candidateOptions
 			return out, comment, options, rest, nil
+		} else {
+			lastErr = err
 		}

 		in = rest
 		continue
 	}

+	if lastErr != nil {
+		return nil, "", nil, nil, fmt.Errorf("ssh: no key found; last parsing error for ignored line: %w", lastErr)
+	}
+
 	return nil, "", nil, nil, errors.New("ssh: no key found")
 }

@@ -395,11 +410,11 @@ func NewSignerWithAlgorithms(signer AlgorithmSigner, algorithms []string) (Multi
 	}

 	for _, algo := range algorithms {
-		if !contains(supportedAlgos, algo) {
+		if !slices.Contains(supportedAlgos, algo) {
 			return nil, fmt.Errorf("ssh: algorithm %q is not supported for key type %q",
 				algo, signer.PublicKey().Type())
 		}
-		if !contains(signerAlgos, algo) {
+		if !slices.Contains(signerAlgos, algo) {
 			return nil, fmt.Errorf("ssh: algorithm %q is restricted for the provided signer", algo)
 		}
 	}
@@ -486,10 +501,13 @@ func (r *rsaPublicKey) Marshal() []byte {

 func (r *rsaPublicKey) Verify(data []byte, sig *Signature) error {
 	supportedAlgos := algorithmsForKeyFormat(r.Type())
-	if !contains(supportedAlgos, sig.Format) {
+	if !slices.Contains(supportedAlgos, sig.Format) {
 		return fmt.Errorf("ssh: signature type %s for key type %s", sig.Format, r.Type())
 	}
-	hash := hashFuncs[sig.Format]
+	hash, err := hashFunc(sig.Format)
+	if err != nil {
+		return err
+	}
 	h := hash.New()
 	h.Write(data)
 	digest := h.Sum(nil)
@@ -606,7 +624,11 @@ func (k *dsaPublicKey) Verify(data []byte, sig *Signature) error {
 	if sig.Format != k.Type() {
 		return fmt.Errorf("ssh: signature type %s for key type %s", sig.Format, k.Type())
 	}
-	h := hashFuncs[sig.Format].New()
+	hash, err := hashFunc(sig.Format)
+	if err != nil {
+		return err
+	}
+	h := hash.New()
 	h.Write(data)
 	digest := h.Sum(nil)

@@ -651,7 +673,11 @@ func (k *dsaPrivateKey) SignWithAlgorithm(rand io.Reader, data []byte, algorithm
 		return nil, fmt.Errorf("ssh: unsupported signature algorithm %s", algorithm)
 	}

-	h := hashFuncs[k.PublicKey().Type()].New()
+	hash, err := hashFunc(k.PublicKey().Type())
+	if err != nil {
+		return nil, err
+	}
+	h := hash.New()
 	h.Write(data)
 	digest := h.Sum(nil)
 	r, s, err := dsa.Sign(rand, k.PrivateKey, digest)
@@ -801,8 +827,11 @@ func (k *ecdsaPublicKey) Verify(data []byte, sig *Signature) error {
 	if sig.Format != k.Type() {
 		return fmt.Errorf("ssh: signature type %s for key type %s", sig.Format, k.Type())
 	}
-
-	h := hashFuncs[sig.Format].New()
+	hash, err := hashFunc(sig.Format)
+	if err != nil {
+		return err
+	}
+	h := hash.New()
 	h.Write(data)
 	digest := h.Sum(nil)

@@ -905,8 +934,11 @@ func (k *skECDSAPublicKey) Verify(data []byte, sig *Signature) error {
 	if sig.Format != k.Type() {
 		return fmt.Errorf("ssh: signature type %s for key type %s", sig.Format, k.Type())
 	}
-
-	h := hashFuncs[sig.Format].New()
+	hash, err := hashFunc(sig.Format)
+	if err != nil {
+		return err
+	}
+	h := hash.New()
 	h.Write([]byte(k.application))
 	appDigest := h.Sum(nil)

@@ -1009,7 +1041,11 @@ func (k *skEd25519PublicKey) Verify(data []byte, sig *Signature) error {
 		return fmt.Errorf("invalid size %d for Ed25519 public key", l)
 	}

-	h := hashFuncs[sig.Format].New()
+	hash, err := hashFunc(sig.Format)
+	if err != nil {
+		return err
+	}
+	h := hash.New()
 	h.Write([]byte(k.application))
 	appDigest := h.Sum(nil)

@@ -1112,11 +1148,14 @@ func (s *wrappedSigner) SignWithAlgorithm(rand io.Reader, data []byte, algorithm
 		algorithm = s.pubKey.Type()
 	}

-	if !contains(s.Algorithms(), algorithm) {
+	if !slices.Contains(s.Algorithms(), algorithm) {
 		return nil, fmt.Errorf("ssh: unsupported signature algorithm %q for key format %q", algorithm, s.pubKey.Type())
 	}

-	hashFunc := hashFuncs[algorithm]
+	hashFunc, err := hashFunc(algorithm)
+	if err != nil {
+		return nil, err
+	}
 	var digest []byte
 	if hashFunc != 0 {
 		h := hashFunc.New()
@@ -7,11 +7,13 @@ package ssh
 // Message authentication support

 import (
+	"crypto/fips140"
 	"crypto/hmac"
 	"crypto/sha1"
 	"crypto/sha256"
 	"crypto/sha512"
 	"hash"
+	"slices"
 )

 type macMode struct {
@@ -46,23 +48,37 @@ func (t truncatingMAC) Size() int {

 func (t truncatingMAC) BlockSize() int { return t.hmac.BlockSize() }

-var macModes = map[string]*macMode{
-	HMACSHA512ETM: {64, true, func(key []byte) hash.Hash {
+// macModes defines the supported MACs. MACs not included are not supported
+// and will not be negotiated, even if explicitly configured. When FIPS mode is
+// enabled, only FIPS-approved algorithms are included.
+var macModes = map[string]*macMode{}
+
+func init() {
+	macModes[HMACSHA512ETM] = &macMode{64, true, func(key []byte) hash.Hash {
 		return hmac.New(sha512.New, key)
-	}},
-	HMACSHA256ETM: {32, true, func(key []byte) hash.Hash {
+	}}
+	macModes[HMACSHA256ETM] = &macMode{32, true, func(key []byte) hash.Hash {
 		return hmac.New(sha256.New, key)
-	}},
-	HMACSHA512: {64, false, func(key []byte) hash.Hash {
+	}}
+	macModes[HMACSHA512] = &macMode{64, false, func(key []byte) hash.Hash {
 		return hmac.New(sha512.New, key)
-	}},
-	HMACSHA256: {32, false, func(key []byte) hash.Hash {
+	}}
+	macModes[HMACSHA256] = &macMode{32, false, func(key []byte) hash.Hash {
 		return hmac.New(sha256.New, key)
-	}},
-	HMACSHA1: {20, false, func(key []byte) hash.Hash {
+	}}
+
+	if fips140.Enabled() {
+		defaultMACs = slices.DeleteFunc(defaultMACs, func(algo string) bool {
+			_, ok := macModes[algo]
+			return !ok
+		})
+		return
+	}
+
+	macModes[HMACSHA1] = &macMode{20, false, func(key []byte) hash.Hash {
 		return hmac.New(sha1.New, key)
-	}},
-	InsecureHMACSHA196: {20, false, func(key []byte) hash.Hash {
+	}}
+	macModes[InsecureHMACSHA196] = &macMode{20, false, func(key []byte) hash.Hash {
 		return truncatingMAC{12, hmac.New(sha1.New, key)}
-	}},
+	}}
 }
@@ -10,6 +10,7 @@ import (
 	"fmt"
 	"io"
 	"net"
+	"slices"
 	"strings"
 )

@@ -43,6 +44,9 @@ type Permissions struct {
 	// pass data from the authentication callbacks to the server
 	// application layer.
 	Extensions map[string]string
+
+	// ExtraData allows to store user defined data.
+	ExtraData map[any]any
 }

 type GSSAPIWithMICConfig struct {
@@ -126,6 +130,21 @@ type ServerConfig struct {
 	// Permissions.Extensions entry.
 	PublicKeyCallback func(conn ConnMetadata, key PublicKey) (*Permissions, error)

+	// VerifiedPublicKeyCallback, if non-nil, is called after a client
+	// successfully confirms having control over a key that was previously
+	// approved by PublicKeyCallback. The permissions object passed to the
+	// callback is the one returned by PublicKeyCallback for the given public
+	// key and its ownership is transferred to the callback. The returned
+	// Permissions object can be the same object, optionally modified, or a
+	// completely new object. If VerifiedPublicKeyCallback is non-nil,
+	// PublicKeyCallback is not allowed to return a PartialSuccessError, which
+	// can instead be returned by VerifiedPublicKeyCallback.
+	//
+	// VerifiedPublicKeyCallback does not affect which authentication methods
+	// are included in the list of methods that can be attempted by the client.
+	VerifiedPublicKeyCallback func(conn ConnMetadata, key PublicKey, permissions *Permissions,
+		signatureAlgorithm string) (*Permissions, error)
+
 	// KeyboardInteractiveCallback, if non-nil, is called when
 	// keyboard-interactive authentication is selected (RFC
 	// 4256). The client object's Challenge function should be
@@ -246,7 +265,7 @@ func NewServerConn(c net.Conn, config *ServerConfig) (*ServerConn, <-chan NewCha
 		fullConf.PublicKeyAuthAlgorithms = defaultPubKeyAuthAlgos
 	} else {
 		for _, algo := range fullConf.PublicKeyAuthAlgorithms {
-			if !contains(SupportedAlgorithms().PublicKeyAuths, algo) && !contains(InsecureAlgorithms().PublicKeyAuths, algo) {
+			if !slices.Contains(SupportedAlgorithms().PublicKeyAuths, algo) && !slices.Contains(InsecureAlgorithms().PublicKeyAuths, algo) {
 				c.Close()
 				return nil, nil, nil, fmt.Errorf("ssh: unsupported public key authentication algorithm %s", algo)
 			}
@@ -631,7 +650,7 @@ userAuthLoop:
 				return nil, parseError(msgUserAuthRequest)
 			}
 			algo := string(algoBytes)
-			if !contains(config.PublicKeyAuthAlgorithms, underlyingAlgo(algo)) {
+			if !slices.Contains(config.PublicKeyAuthAlgorithms, underlyingAlgo(algo)) {
 				authErr = fmt.Errorf("ssh: algorithm %q not accepted", algo)
 				break
 			}
@@ -652,6 +671,9 @@ userAuthLoop:
 				candidate.pubKeyData = pubKeyData
 				candidate.perms, candidate.result = authConfig.PublicKeyCallback(s, pubKey)
 				_, isPartialSuccessError := candidate.result.(*PartialSuccessError)
+				if isPartialSuccessError && config.VerifiedPublicKeyCallback != nil {
+					return nil, errors.New("ssh: invalid library usage: PublicKeyCallback must not return partial success when VerifiedPublicKeyCallback is defined")
+				}

 				if (candidate.result == nil || isPartialSuccessError) &&
 					candidate.perms != nil &&
@@ -695,7 +717,7 @@ userAuthLoop:
 				// ssh-rsa-cert-v01@openssh.com algorithm with ssh-rsa public
 				// key type. The algorithm and public key type must be
 				// consistent: both must be certificate algorithms, or neither.
-				if !contains(algorithmsForKeyFormat(pubKey.Type()), algo) {
+				if !slices.Contains(algorithmsForKeyFormat(pubKey.Type()), algo) {
 					authErr = fmt.Errorf("ssh: public key type %q not compatible with selected algorithm %q",
 						pubKey.Type(), algo)
 					break
@@ -705,7 +727,7 @@ userAuthLoop:
 				// algorithm name that corresponds to algo with
 				// sig.Format.  This is usually the same, but
 				// for certs, the names differ.
-				if !contains(config.PublicKeyAuthAlgorithms, sig.Format) {
+				if !slices.Contains(config.PublicKeyAuthAlgorithms, sig.Format) {
 					authErr = fmt.Errorf("ssh: algorithm %q not accepted", sig.Format)
 					break
 				}
@@ -722,6 +744,12 @@ userAuthLoop:

 				authErr = candidate.result
 				perms = candidate.perms
+				if authErr == nil && config.VerifiedPublicKeyCallback != nil {
+					// Only call VerifiedPublicKeyCallback after the key has been accepted
+					// and successfully verified. If authErr is non-nil, the key is not
+					// considered verified and the callback must not run.
+					perms, authErr = config.VerifiedPublicKeyCallback(s, pubKey, perms, algo)
+				}
 			}
 		case "gssapi-with-mic":
 			if authConfig.GSSAPIWithMICConfig == nil {
@@ -8,6 +8,7 @@ import (
 	"bufio"
 	"bytes"
 	"errors"
+	"fmt"
 	"io"
 	"log"
 )
@@ -254,6 +255,9 @@ var (
 // (to setup server->client keys) or clientKeys (for client->server keys).
 func newPacketCipher(d direction, algs DirectionAlgorithms, kex *kexResult) (packetCipher, error) {
 	cipherMode := cipherModes[algs.Cipher]
+	if cipherMode == nil {
+		return nil, fmt.Errorf("ssh: unsupported cipher %v", algs.Cipher)
+	}

 	iv := make([]byte, cipherMode.ivSize)
 	key := make([]byte, cipherMode.keySize)
@@ -299,7 +299,7 @@ func escape(w writer, s string) error {
 		case '\r':
 			esc = "&#13;"
 		default:
-			panic("unrecognized escape character")
+			panic("html: unrecognized escape character")
 		}
 		s = s[i+1:]
 		if _, err := w.WriteString(esc); err != nil {
@@ -136,7 +136,7 @@ func (p *parser) indexOfElementInScope(s scope, matchTags ...a.Atom) int {
 					return -1
 				}
 			default:
-				panic("unreachable")
+				panic(fmt.Sprintf("html: internal error: indexOfElementInScope unknown scope: %d", s))
 			}
 		}
 		switch s {
@@ -179,7 +179,7 @@ func (p *parser) clearStackToContext(s scope) {
 				return
 			}
 		default:
-			panic("unreachable")
+			panic(fmt.Sprintf("html: internal error: clearStackToContext unknown scope: %d", s))
 		}
 	}
 }
@@ -231,7 +231,14 @@ func (p *parser) addChild(n *Node) {
 	}

 	if n.Type == ElementNode {
-		p.oe = append(p.oe, n)
+		p.insertOpenElement(n)
+	}
+}
+
+func (p *parser) insertOpenElement(n *Node) {
+	p.oe = append(p.oe, n)
+	if len(p.oe) > 512 {
+		panic("html: open stack of elements exceeds 512 nodes")
 	}
 }

@@ -810,7 +817,7 @@ func afterHeadIM(p *parser) bool {
 			p.im = inFramesetIM
 			return true
 		case a.Base, a.Basefont, a.Bgsound, a.Link, a.Meta, a.Noframes, a.Script, a.Style, a.Template, a.Title:
-			p.oe = append(p.oe, p.head)
+			p.insertOpenElement(p.head)
 			defer p.oe.remove(p.head)
 			return inHeadIM(p)
 		case a.Head:
@@ -1678,7 +1685,7 @@ func inTableBodyIM(p *parser) bool {
 	return inTableIM(p)
 }

-// Section 12.2.6.4.14.
+// Section 13.2.6.4.14.
 func inRowIM(p *parser) bool {
 	switch p.tok.Type {
 	case StartTagToken:
@@ -1690,7 +1697,9 @@ func inRowIM(p *parser) bool {
 			p.im = inCellIM
 			return true
 		case a.Caption, a.Col, a.Colgroup, a.Tbody, a.Tfoot, a.Thead, a.Tr:
-			if p.popUntil(tableScope, a.Tr) {
+			if p.elementInScope(tableScope, a.Tr) {
+				p.clearStackToContext(tableRowScope)
+				p.oe.pop()
 				p.im = inTableBodyIM
 				return false
 			}
@@ -1700,22 +1709,28 @@ func inRowIM(p *parser) bool {
 	case EndTagToken:
 		switch p.tok.DataAtom {
 		case a.Tr:
-			if p.popUntil(tableScope, a.Tr) {
+			if p.elementInScope(tableScope, a.Tr) {
+				p.clearStackToContext(tableRowScope)
+				p.oe.pop()
 				p.im = inTableBodyIM
 				return true
 			}
 			// Ignore the token.
 			return true
 		case a.Table:
-			if p.popUntil(tableScope, a.Tr) {
+			if p.elementInScope(tableScope, a.Tr) {
+				p.clearStackToContext(tableRowScope)
+				p.oe.pop()
 				p.im = inTableBodyIM
 				return false
 			}
 			// Ignore the token.
 			return true
 		case a.Tbody, a.Tfoot, a.Thead:
-			if p.elementInScope(tableScope, p.tok.DataAtom) {
-				p.parseImpliedToken(EndTagToken, a.Tr, a.Tr.String())
+			if p.elementInScope(tableScope, p.tok.DataAtom) && p.elementInScope(tableScope, a.Tr) {
+				p.clearStackToContext(tableRowScope)
+				p.oe.pop()
+				p.im = inTableBodyIM
 				return false
 			}
 			// Ignore the token.
@@ -2222,16 +2237,20 @@ func parseForeignContent(p *parser) bool {
 			p.acknowledgeSelfClosingTag()
 		}
 	case EndTagToken:
+		if strings.EqualFold(p.oe[len(p.oe)-1].Data, p.tok.Data) {
+			p.oe = p.oe[:len(p.oe)-1]
+			return true
+		}
 		for i := len(p.oe) - 1; i >= 0; i-- {
-			if p.oe[i].Namespace == "" {
-				return p.im(p)
-			}
 			if strings.EqualFold(p.oe[i].Data, p.tok.Data) {
 				p.oe = p.oe[:i]
+				return true
+			}
+			if i > 0 && p.oe[i-1].Namespace == "" {
 				break
 			}
 		}
-		return true
+		return p.im(p)
 	default:
 		// Ignore the token.
 	}
@@ -2312,9 +2331,13 @@ func (p *parser) parseCurrentToken() {
 	}
 }

-func (p *parser) parse() error {
+func (p *parser) parse() (err error) {
+	defer func() {
+		if panicErr := recover(); panicErr != nil {
+			err = fmt.Errorf("%s", panicErr)
+		}
+	}()
 	// Iterate until EOF. Any other error will cause an early return.
-	var err error
 	for err != io.EOF {
 		// CDATA sections are allowed only in foreign content.
 		n := p.oe.top()
@@ -2343,6 +2366,8 @@ func (p *parser) parse() error {
 // <tag>s. Conversely, explicit <tag>s in r's data can be silently dropped,
 // with no corresponding node in the resulting tree.
 //
+// Parse will reject HTML that is nested deeper than 512 elements.
+//
 // The input is assumed to be UTF-8 encoded.
 func Parse(r io.Reader) (*Node, error) {
 	return ParseWithOptions(r)
@@ -184,7 +184,7 @@ func render1(w writer, n *Node) error {
 		return err
 	}

-	// Add initial newline where there is danger of a newline beging ignored.
+	// Add initial newline where there is danger of a newline being ignored.
 	if c := n.FirstChild; c != nil && c.Type == TextNode && strings.HasPrefix(c.Data, "\n") {
 		switch n.Data {
 		case "pre", "listing", "textarea":
@@ -27,6 +27,7 @@ import (
 //   - If the resulting value is zero or out of range, use a default.
 type http2Config struct {
 	MaxConcurrentStreams         uint32
+	StrictMaxConcurrentRequests  bool
 	MaxDecoderHeaderTableSize    uint32
 	MaxEncoderHeaderTableSize    uint32
 	MaxReadFrameSize             uint32
@@ -64,12 +65,13 @@ func configFromServer(h1 *http.Server, h2 *Server) http2Config {
 // (the net/http Transport).
 func configFromTransport(h2 *Transport) http2Config {
 	conf := http2Config{
-		MaxEncoderHeaderTableSize: h2.MaxEncoderHeaderTableSize,
-		MaxDecoderHeaderTableSize: h2.MaxDecoderHeaderTableSize,
-		MaxReadFrameSize:          h2.MaxReadFrameSize,
-		SendPingTimeout:           h2.ReadIdleTimeout,
-		PingTimeout:               h2.PingTimeout,
-		WriteByteTimeout:          h2.WriteByteTimeout,
+		StrictMaxConcurrentRequests: h2.StrictMaxConcurrentStreams,
+		MaxEncoderHeaderTableSize:   h2.MaxEncoderHeaderTableSize,
+		MaxDecoderHeaderTableSize:   h2.MaxDecoderHeaderTableSize,
+		MaxReadFrameSize:            h2.MaxReadFrameSize,
+		SendPingTimeout:             h2.ReadIdleTimeout,
+		PingTimeout:                 h2.PingTimeout,
+		WriteByteTimeout:            h2.WriteByteTimeout,
 	}

 	// Unlike most config fields, where out-of-range values revert to the default,
@@ -128,6 +130,9 @@ func fillNetHTTPConfig(conf *http2Config, h2 *http.HTTP2Config) {
 	if h2.MaxConcurrentStreams != 0 {
 		conf.MaxConcurrentStreams = uint32(h2.MaxConcurrentStreams)
 	}
+	if http2ConfigStrictMaxConcurrentRequests(h2) {
+		conf.StrictMaxConcurrentRequests = true
+	}
 	if h2.MaxEncoderHeaderTableSize != 0 {
 		conf.MaxEncoderHeaderTableSize = uint32(h2.MaxEncoderHeaderTableSize)
 	}
@@ -0,0 +1,15 @@
+// Copyright 2025 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+//go:build !go1.26
+
+package http2
+
+import (
+	"net/http"
+)
+
+func http2ConfigStrictMaxConcurrentRequests(h2 *http.HTTP2Config) bool {
+	return false
+}
@@ -0,0 +1,15 @@
+// Copyright 2025 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+//go:build go1.26
+
+package http2
+
+import (
+	"net/http"
+)
+
+func http2ConfigStrictMaxConcurrentRequests(h2 *http.HTTP2Config) bool {
+	return h2.StrictMaxConcurrentRequests
+}
@@ -347,7 +347,7 @@ func (fr *Framer) maxHeaderListSize() uint32 {
 func (f *Framer) startWrite(ftype FrameType, flags Flags, streamID uint32) {
 	// Write the FrameHeader.
 	f.wbuf = append(f.wbuf[:0],
-		0, // 3 bytes of length, filled in in endWrite
+		0, // 3 bytes of length, filled in endWrite
 		0,
 		0,
 		byte(ftype),
@@ -1152,6 +1152,15 @@ type PriorityFrame struct {
 	PriorityParam
 }

+var defaultRFC9218Priority = PriorityParam{
+	incremental: 0,
+	urgency:     3,
+}
+
+// Note that HTTP/2 has had two different prioritization schemes, and
+// PriorityParam struct below is a superset of both schemes. The exported
+// symbols are from RFC 7540 and the non-exported ones are from RFC 9218.
+
 // PriorityParam are the stream prioritzation parameters.
 type PriorityParam struct {
 	// StreamDep is a 31-bit stream identifier for the
@@ -1167,6 +1176,20 @@ type PriorityParam struct {
 	// the spec, "Add one to the value to obtain a weight between
 	// 1 and 256."
 	Weight uint8
+
+	// "The urgency (u) parameter value is Integer (see Section 3.3.1 of
+	// [STRUCTURED-FIELDS]), between 0 and 7 inclusive, in descending order of
+	// priority. The default is 3."
+	urgency uint8
+
+	// "The incremental (i) parameter value is Boolean (see Section 3.3.6 of
+	// [STRUCTURED-FIELDS]). It indicates if an HTTP response can be processed
+	// incrementally, i.e., provide some meaningful output as chunks of the
+	// response arrive."
+	//
+	// We use uint8 (i.e. 0 is false, 1 is true) instead of bool so we can
+	// avoid unnecessary type conversions and because either type takes 1 byte.
+	incremental uint8
 }

 func (p PriorityParam) IsZero() bool {
@@ -34,7 +34,6 @@ var (
 	VerboseLogs    bool
 	logFrameWrites bool
 	logFrameReads  bool
-	inTests        bool

 	// Enabling extended CONNECT by causes browsers to attempt to use
 	// WebSockets-over-HTTP/2. This results in problems when the server's websocket
@@ -181,6 +181,10 @@ type Server struct {
 type serverInternalState struct {
 	mu          sync.Mutex
 	activeConns map[*serverConn]struct{}
+
+	// Pool of error channels. This is per-Server rather than global
+	// because channels can't be reused across synctest bubbles.
+	errChanPool sync.Pool
 }

 func (s *serverInternalState) registerConn(sc *serverConn) {
@@ -212,6 +216,27 @@ func (s *serverInternalState) startGracefulShutdown() {
 	s.mu.Unlock()
 }

+// Global error channel pool used for uninitialized Servers.
+// We use a per-Server pool when possible to avoid using channels across synctest bubbles.
+var errChanPool = sync.Pool{
+	New: func() any { return make(chan error, 1) },
+}
+
+func (s *serverInternalState) getErrChan() chan error {
+	if s == nil {
+		return errChanPool.Get().(chan error) // Server used without calling ConfigureServer
+	}
+	return s.errChanPool.Get().(chan error)
+}
+
+func (s *serverInternalState) putErrChan(ch chan error) {
+	if s == nil {
+		errChanPool.Put(ch) // Server used without calling ConfigureServer
+		return
+	}
+	s.errChanPool.Put(ch)
+}
+
 // ConfigureServer adds HTTP/2 support to a net/http Server.
 //
 // The configuration conf may be nil.
@@ -224,7 +249,10 @@ func ConfigureServer(s *http.Server, conf *Server) error {
 	if conf == nil {
 		conf = new(Server)
 	}
-	conf.state = &serverInternalState{activeConns: make(map[*serverConn]struct{})}
+	conf.state = &serverInternalState{
+		activeConns: make(map[*serverConn]struct{}),
+		errChanPool: sync.Pool{New: func() any { return make(chan error, 1) }},
+	}
 	if h1, h2 := s, conf; h2.IdleTimeout == 0 {
 		if h1.IdleTimeout != 0 {
 			h2.IdleTimeout = h1.IdleTimeout
@@ -1124,25 +1152,6 @@ func (sc *serverConn) readPreface() error {
 	}
 }

-var errChanPool = sync.Pool{
-	New: func() interface{} { return make(chan error, 1) },
-}
-
-func getErrChan() chan error {
-	if inTests {
-		// Channels cannot be reused across synctest tests.
-		return make(chan error, 1)
-	} else {
-		return errChanPool.Get().(chan error)
-	}
-}
-
-func putErrChan(ch chan error) {
-	if !inTests {
-		errChanPool.Put(ch)
-	}
-}
-
 var writeDataPool = sync.Pool{
 	New: func() interface{} { return new(writeData) },
 }
@@ -1150,7 +1159,7 @@ var writeDataPool = sync.Pool{
 // writeDataFromHandler writes DATA response frames from a handler on
 // the given stream.
 func (sc *serverConn) writeDataFromHandler(stream *stream, data []byte, endStream bool) error {
-	ch := getErrChan()
+	ch := sc.srv.state.getErrChan()
 	writeArg := writeDataPool.Get().(*writeData)
 	*writeArg = writeData{stream.id, data, endStream}
 	err := sc.writeFrameFromHandler(FrameWriteRequest{
@@ -1182,7 +1191,7 @@ func (sc *serverConn) writeDataFromHandler(stream *stream, data []byte, endStrea
 			return errStreamClosed
 		}
 	}
-	putErrChan(ch)
+	sc.srv.state.putErrChan(ch)
 	if frameWriteDone {
 		writeDataPool.Put(writeArg)
 	}
@@ -2436,7 +2445,7 @@ func (sc *serverConn) writeHeaders(st *stream, headerData *writeResHeaders) erro
 		// waiting for this frame to be written, so an http.Flush mid-handler
 		// writes out the correct value of keys, before a handler later potentially
 		// mutates it.
-		errc = getErrChan()
+		errc = sc.srv.state.getErrChan()
 	}
 	if err := sc.writeFrameFromHandler(FrameWriteRequest{
 		write:  headerData,
@@ -2448,7 +2457,7 @@ func (sc *serverConn) writeHeaders(st *stream, headerData *writeResHeaders) erro
 	if errc != nil {
 		select {
 		case err := <-errc:
-			putErrChan(errc)
+			sc.srv.state.putErrChan(errc)
 			return err
 		case <-sc.doneServing:
 			return errClientDisconnected
@@ -3129,7 +3138,7 @@ func (w *responseWriter) Push(target string, opts *http.PushOptions) error {
 		method: opts.Method,
 		url:    u,
 		header: cloneHeader(opts.Header),
-		done:   getErrChan(),
+		done:   sc.srv.state.getErrChan(),
 	}

 	select {
@@ -3146,7 +3155,7 @@ func (w *responseWriter) Push(target string, opts *http.PushOptions) error {
 	case <-st.cw:
 		return errStreamClosed
 	case err := <-msg.done:
-		putErrChan(msg.done)
+		sc.srv.state.putErrChan(msg.done)
 		return err
 	}
 }
@@ -355,6 +355,7 @@ type ClientConn struct {
 	readIdleTimeout             time.Duration
 	pingTimeout                 time.Duration
 	extendedConnectAllowed      bool
+	strictMaxConcurrentStreams  bool

 	// rstStreamPingsBlocked works around an unfortunate gRPC behavior.
 	// gRPC strictly limits the number of PING frames that it will receive.
@@ -784,7 +785,8 @@ func (t *Transport) newClientConn(c net.Conn, singleUse bool) (*ClientConn, erro
 		initialWindowSize:           65535,    // spec default
 		initialStreamRecvWindowSize: conf.MaxUploadBufferPerStream,
 		maxConcurrentStreams:        initialMaxConcurrentStreams, // "infinite", per spec. Use a smaller value until we have received server settings.
-		peerMaxHeaderListSize:       0xffffffffffffffff,          // "infinite", per spec. Use 2^64-1 instead.
+		strictMaxConcurrentStreams:  conf.StrictMaxConcurrentRequests,
+		peerMaxHeaderListSize:       0xffffffffffffffff, // "infinite", per spec. Use 2^64-1 instead.
 		streams:                     make(map[uint32]*clientStream),
 		singleUse:                   singleUse,
 		seenSettingsChan:            make(chan struct{}),
@@ -1018,7 +1020,7 @@ func (cc *ClientConn) idleStateLocked() (st clientConnIdleState) {
 		return
 	}
 	var maxConcurrentOkay bool
-	if cc.t.StrictMaxConcurrentStreams {
+	if cc.strictMaxConcurrentStreams {
 		// We'll tell the caller we can take a new request to
 		// prevent the caller from dialing a new TCP
 		// connection, but then we'll block later before
@@ -42,6 +42,8 @@ type OpenStreamOptions struct {
 	// PusherID is zero if the stream was initiated by the client. Otherwise,
 	// PusherID names the stream that pushed the newly opened stream.
 	PusherID uint32
+	// priority is used to set the priority of the newly opened stream.
+	priority PriorityParam
 }

 // FrameWriteRequest is a request to write a frame.
@@ -11,7 +11,7 @@ import (
 )

 // RFC 7540, Section 5.3.5: the default weight is 16.
-const priorityDefaultWeight = 15 // 16 = 15 + 1
+const priorityDefaultWeightRFC7540 = 15 // 16 = 15 + 1

 // PriorityWriteSchedulerConfig configures a priorityWriteScheduler.
 type PriorityWriteSchedulerConfig struct {
@@ -66,8 +66,8 @@ func NewPriorityWriteScheduler(cfg *PriorityWriteSchedulerConfig) WriteScheduler
 		}
 	}

-	ws := &priorityWriteScheduler{
-		nodes:                make(map[uint32]*priorityNode),
+	ws := &priorityWriteSchedulerRFC7540{
+		nodes:                make(map[uint32]*priorityNodeRFC7540),
 		maxClosedNodesInTree: cfg.MaxClosedNodesInTree,
 		maxIdleNodesInTree:   cfg.MaxIdleNodesInTree,
 		enableWriteThrottle:  cfg.ThrottleOutOfOrderWrites,
@@ -81,32 +81,32 @@ func NewPriorityWriteScheduler(cfg *PriorityWriteSchedulerConfig) WriteScheduler
 	return ws
 }

-type priorityNodeState int
+type priorityNodeStateRFC7540 int

 const (
-	priorityNodeOpen priorityNodeState = iota
-	priorityNodeClosed
-	priorityNodeIdle
+	priorityNodeOpenRFC7540 priorityNodeStateRFC7540 = iota
+	priorityNodeClosedRFC7540
+	priorityNodeIdleRFC7540
 )

-// priorityNode is a node in an HTTP/2 priority tree.
+// priorityNodeRFC7540 is a node in an HTTP/2 priority tree.
 // Each node is associated with a single stream ID.
 // See RFC 7540, Section 5.3.
-type priorityNode struct {
-	q            writeQueue        // queue of pending frames to write
-	id           uint32            // id of the stream, or 0 for the root of the tree
-	weight       uint8             // the actual weight is weight+1, so the value is in [1,256]
-	state        priorityNodeState // open | closed | idle
-	bytes        int64             // number of bytes written by this node, or 0 if closed
-	subtreeBytes int64             // sum(node.bytes) of all nodes in this subtree
+type priorityNodeRFC7540 struct {
+	q            writeQueue               // queue of pending frames to write
+	id           uint32                   // id of the stream, or 0 for the root of the tree
+	weight       uint8                    // the actual weight is weight+1, so the value is in [1,256]
+	state        priorityNodeStateRFC7540 // open | closed | idle
+	bytes        int64                    // number of bytes written by this node, or 0 if closed
+	subtreeBytes int64                    // sum(node.bytes) of all nodes in this subtree

 	// These links form the priority tree.
-	parent     *priorityNode
-	kids       *priorityNode // start of the kids list
-	prev, next *priorityNode // doubly-linked list of siblings
+	parent     *priorityNodeRFC7540
+	kids       *priorityNodeRFC7540 // start of the kids list
+	prev, next *priorityNodeRFC7540 // doubly-linked list of siblings
 }

-func (n *priorityNode) setParent(parent *priorityNode) {
+func (n *priorityNodeRFC7540) setParent(parent *priorityNodeRFC7540) {
 	if n == parent {
 		panic("setParent to self")
 	}
@@ -141,7 +141,7 @@ func (n *priorityNode) setParent(parent *priorityNode) {
 	}
 }

-func (n *priorityNode) addBytes(b int64) {
+func (n *priorityNodeRFC7540) addBytes(b int64) {
 	n.bytes += b
 	for ; n != nil; n = n.parent {
 		n.subtreeBytes += b
@@ -154,7 +154,7 @@ func (n *priorityNode) addBytes(b int64) {
 //
 // f(n, openParent) takes two arguments: the node to visit, n, and a bool that is true
 // if any ancestor p of n is still open (ignoring the root node).
-func (n *priorityNode) walkReadyInOrder(openParent bool, tmp *[]*priorityNode, f func(*priorityNode, bool) bool) bool {
+func (n *priorityNodeRFC7540) walkReadyInOrder(openParent bool, tmp *[]*priorityNodeRFC7540, f func(*priorityNodeRFC7540, bool) bool) bool {
 	if !n.q.empty() && f(n, openParent) {
 		return true
 	}
@@ -165,7 +165,7 @@ func (n *priorityNode) walkReadyInOrder(openParent bool, tmp *[]*priorityNode, f
 	// Don't consider the root "open" when updating openParent since
 	// we can't send data frames on the root stream (only control frames).
 	if n.id != 0 {
-		openParent = openParent || (n.state == priorityNodeOpen)
+		openParent = openParent || (n.state == priorityNodeOpenRFC7540)
 	}

 	// Common case: only one kid or all kids have the same weight.
@@ -195,7 +195,7 @@ func (n *priorityNode) walkReadyInOrder(openParent bool, tmp *[]*priorityNode, f
 		*tmp = append(*tmp, n.kids)
 		n.kids.setParent(nil)
 	}
-	sort.Sort(sortPriorityNodeSiblings(*tmp))
+	sort.Sort(sortPriorityNodeSiblingsRFC7540(*tmp))
 	for i := len(*tmp) - 1; i >= 0; i-- {
 		(*tmp)[i].setParent(n) // setParent inserts at the head of n.kids
 	}
@@ -207,11 +207,11 @@ func (n *priorityNode) walkReadyInOrder(openParent bool, tmp *[]*priorityNode, f
 	return false
 }

-type sortPriorityNodeSiblings []*priorityNode
+type sortPriorityNodeSiblingsRFC7540 []*priorityNodeRFC7540

-func (z sortPriorityNodeSiblings) Len() int      { return len(z) }
-func (z sortPriorityNodeSiblings) Swap(i, k int) { z[i], z[k] = z[k], z[i] }
-func (z sortPriorityNodeSiblings) Less(i, k int) bool {
+func (z sortPriorityNodeSiblingsRFC7540) Len() int      { return len(z) }
+func (z sortPriorityNodeSiblingsRFC7540) Swap(i, k int) { z[i], z[k] = z[k], z[i] }
+func (z sortPriorityNodeSiblingsRFC7540) Less(i, k int) bool {
 	// Prefer the subtree that has sent fewer bytes relative to its weight.
 	// See sections 5.3.2 and 5.3.4.
 	wi, bi := float64(z[i].weight+1), float64(z[i].subtreeBytes)
@@ -225,13 +225,13 @@ func (z sortPriorityNodeSiblings) Less(i, k int) bool {
 	return bi/bk <= wi/wk
 }

-type priorityWriteScheduler struct {
+type priorityWriteSchedulerRFC7540 struct {
 	// root is the root of the priority tree, where root.id = 0.
 	// The root queues control frames that are not associated with any stream.
-	root priorityNode
+	root priorityNodeRFC7540

 	// nodes maps stream ids to priority tree nodes.
-	nodes map[uint32]*priorityNode
+	nodes map[uint32]*priorityNodeRFC7540

 	// maxID is the maximum stream id in nodes.
 	maxID uint32
@@ -239,7 +239,7 @@ type priorityWriteScheduler struct {
 	// lists of nodes that have been closed or are idle, but are kept in
 	// the tree for improved prioritization. When the lengths exceed either
 	// maxClosedNodesInTree or maxIdleNodesInTree, old nodes are discarded.
-	closedNodes, idleNodes []*priorityNode
+	closedNodes, idleNodes []*priorityNodeRFC7540

 	// From the config.
 	maxClosedNodesInTree int
@@ -248,19 +248,19 @@ type priorityWriteScheduler struct {
 	enableWriteThrottle  bool

 	// tmp is scratch space for priorityNode.walkReadyInOrder to reduce allocations.
-	tmp []*priorityNode
+	tmp []*priorityNodeRFC7540

 	// pool of empty queues for reuse.
 	queuePool writeQueuePool
 }

-func (ws *priorityWriteScheduler) OpenStream(streamID uint32, options OpenStreamOptions) {
+func (ws *priorityWriteSchedulerRFC7540) OpenStream(streamID uint32, options OpenStreamOptions) {
 	// The stream may be currently idle but cannot be opened or closed.
 	if curr := ws.nodes[streamID]; curr != nil {
-		if curr.state != priorityNodeIdle {
+		if curr.state != priorityNodeIdleRFC7540 {
 			panic(fmt.Sprintf("stream %d already opened", streamID))
 		}
-		curr.state = priorityNodeOpen
+		curr.state = priorityNodeOpenRFC7540
 		return
 	}

@@ -272,11 +272,11 @@ func (ws *priorityWriteScheduler) OpenStream(streamID uint32, options OpenStream
 	if parent == nil {
 		parent = &ws.root
 	}
-	n := &priorityNode{
+	n := &priorityNodeRFC7540{
 		q:      *ws.queuePool.get(),
 		id:     streamID,
-		weight: priorityDefaultWeight,
-		state:  priorityNodeOpen,
+		weight: priorityDefaultWeightRFC7540,
+		state:  priorityNodeOpenRFC7540,
 	}
 	n.setParent(parent)
 	ws.nodes[streamID] = n
@@ -285,19 +285,19 @@ func (ws *priorityWriteScheduler) OpenStream(streamID uint32, options OpenStream
 	}
 }

-func (ws *priorityWriteScheduler) CloseStream(streamID uint32) {
+func (ws *priorityWriteSchedulerRFC7540) CloseStream(streamID uint32) {
 	if streamID == 0 {
 		panic("violation of WriteScheduler interface: cannot close stream 0")
 	}
 	if ws.nodes[streamID] == nil {
 		panic(fmt.Sprintf("violation of WriteScheduler interface: unknown stream %d", streamID))
 	}
-	if ws.nodes[streamID].state != priorityNodeOpen {
+	if ws.nodes[streamID].state != priorityNodeOpenRFC7540 {
 		panic(fmt.Sprintf("violation of WriteScheduler interface: stream %d already closed", streamID))
 	}

 	n := ws.nodes[streamID]
-	n.state = priorityNodeClosed
+	n.state = priorityNodeClosedRFC7540
 	n.addBytes(-n.bytes)

 	q := n.q
@@ -310,7 +310,7 @@ func (ws *priorityWriteScheduler) CloseStream(streamID uint32) {
 	}
 }

-func (ws *priorityWriteScheduler) AdjustStream(streamID uint32, priority PriorityParam) {
+func (ws *priorityWriteSchedulerRFC7540) AdjustStream(streamID uint32, priority PriorityParam) {
 	if streamID == 0 {
 		panic("adjustPriority on root")
 	}
@@ -324,11 +324,11 @@ func (ws *priorityWriteScheduler) AdjustStream(streamID uint32, priority Priorit
 			return
 		}
 		ws.maxID = streamID
-		n = &priorityNode{
+		n = &priorityNodeRFC7540{
 			q:      *ws.queuePool.get(),
 			id:     streamID,
-			weight: priorityDefaultWeight,
-			state:  priorityNodeIdle,
+			weight: priorityDefaultWeightRFC7540,
+			state:  priorityNodeIdleRFC7540,
 		}
 		n.setParent(&ws.root)
 		ws.nodes[streamID] = n
@@ -340,7 +340,7 @@ func (ws *priorityWriteScheduler) AdjustStream(streamID uint32, priority Priorit
 	parent := ws.nodes[priority.StreamDep]
 	if parent == nil {
 		n.setParent(&ws.root)
-		n.weight = priorityDefaultWeight
+		n.weight = priorityDefaultWeightRFC7540
 		return
 	}

@@ -381,8 +381,8 @@ func (ws *priorityWriteScheduler) AdjustStream(streamID uint32, priority Priorit
 	n.weight = priority.Weight
 }

-func (ws *priorityWriteScheduler) Push(wr FrameWriteRequest) {
-	var n *priorityNode
+func (ws *priorityWriteSchedulerRFC7540) Push(wr FrameWriteRequest) {
+	var n *priorityNodeRFC7540
 	if wr.isControl() {
 		n = &ws.root
 	} else {
@@ -401,8 +401,8 @@ func (ws *priorityWriteScheduler) Push(wr FrameWriteRequest) {
 	n.q.push(wr)
 }

-func (ws *priorityWriteScheduler) Pop() (wr FrameWriteRequest, ok bool) {
-	ws.root.walkReadyInOrder(false, &ws.tmp, func(n *priorityNode, openParent bool) bool {
+func (ws *priorityWriteSchedulerRFC7540) Pop() (wr FrameWriteRequest, ok bool) {
+	ws.root.walkReadyInOrder(false, &ws.tmp, func(n *priorityNodeRFC7540, openParent bool) bool {
 		limit := int32(math.MaxInt32)
 		if openParent {
 			limit = ws.writeThrottleLimit
@@ -428,7 +428,7 @@ func (ws *priorityWriteScheduler) Pop() (wr FrameWriteRequest, ok bool) {
 	return wr, ok
 }

-func (ws *priorityWriteScheduler) addClosedOrIdleNode(list *[]*priorityNode, maxSize int, n *priorityNode) {
+func (ws *priorityWriteSchedulerRFC7540) addClosedOrIdleNode(list *[]*priorityNodeRFC7540, maxSize int, n *priorityNodeRFC7540) {
 	if maxSize == 0 {
 		return
 	}
@@ -442,7 +442,7 @@ func (ws *priorityWriteScheduler) addClosedOrIdleNode(list *[]*priorityNode, max
 	*list = append(*list, n)
 }

-func (ws *priorityWriteScheduler) removeNode(n *priorityNode) {
+func (ws *priorityWriteSchedulerRFC7540) removeNode(n *priorityNodeRFC7540) {
 	for n.kids != nil {
 		n.kids.setParent(n.parent)
 	}
@@ -0,0 +1,209 @@
+// Copyright 2025 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package http2
+
+import (
+	"fmt"
+	"math"
+)
+
+type streamMetadata struct {
+	location *writeQueue
+	priority PriorityParam
+}
+
+type priorityWriteSchedulerRFC9218 struct {
+	// control contains control frames (SETTINGS, PING, etc.).
+	control writeQueue
+
+	// heads contain the head of a circular list of streams.
+	// We put these heads within a nested array that represents urgency and
+	// incremental, as defined in
+	// https://www.rfc-editor.org/rfc/rfc9218.html#name-priority-parameters.
+	// 8 represents u=0 up to u=7, and 2 represents i=false and i=true.
+	heads [8][2]*writeQueue
+
+	// streams contains a mapping between each stream ID and their metadata, so
+	// we can quickly locate them when needing to, for example, adjust their
+	// priority.
+	streams map[uint32]streamMetadata
+
+	// queuePool are empty queues for reuse.
+	queuePool writeQueuePool
+
+	// prioritizeIncremental is used to determine whether we should prioritize
+	// incremental streams or not, when urgency is the same in a given Pop()
+	// call.
+	prioritizeIncremental bool
+}
+
+func newPriorityWriteSchedulerRFC9128() WriteScheduler {
+	ws := &priorityWriteSchedulerRFC9218{
+		streams: make(map[uint32]streamMetadata),
+	}
+	return ws
+}
+
+func (ws *priorityWriteSchedulerRFC9218) OpenStream(streamID uint32, opt OpenStreamOptions) {
+	if ws.streams[streamID].location != nil {
+		panic(fmt.Errorf("stream %d already opened", streamID))
+	}
+	q := ws.queuePool.get()
+	ws.streams[streamID] = streamMetadata{
+		location: q,
+		priority: opt.priority,
+	}
+
+	u, i := opt.priority.urgency, opt.priority.incremental
+	if ws.heads[u][i] == nil {
+		ws.heads[u][i] = q
+		q.next = q
+		q.prev = q
+	} else {
+		// Queues are stored in a ring.
+		// Insert the new stream before ws.head, putting it at the end of the list.
+		q.prev = ws.heads[u][i].prev
+		q.next = ws.heads[u][i]
+		q.prev.next = q
+		q.next.prev = q
+	}
+}
+
+func (ws *priorityWriteSchedulerRFC9218) CloseStream(streamID uint32) {
+	metadata := ws.streams[streamID]
+	q, u, i := metadata.location, metadata.priority.urgency, metadata.priority.incremental
+	if q == nil {
+		return
+	}
+	if q.next == q {
+		// This was the only open stream.
+		ws.heads[u][i] = nil
+	} else {
+		q.prev.next = q.next
+		q.next.prev = q.prev
+		if ws.heads[u][i] == q {
+			ws.heads[u][i] = q.next
+		}
+	}
+	delete(ws.streams, streamID)
+	ws.queuePool.put(q)
+}
+
+func (ws *priorityWriteSchedulerRFC9218) AdjustStream(streamID uint32, priority PriorityParam) {
+	metadata := ws.streams[streamID]
+	q, u, i := metadata.location, metadata.priority.urgency, metadata.priority.incremental
+	if q == nil {
+		return
+	}
+
+	// Remove stream from current location.
+	if q.next == q {
+		// This was the only open stream.
+		ws.heads[u][i] = nil
+	} else {
+		q.prev.next = q.next
+		q.next.prev = q.prev
+		if ws.heads[u][i] == q {
+			ws.heads[u][i] = q.next
+		}
+	}
+
+	// Insert stream to the new queue.
+	u, i = priority.urgency, priority.incremental
+	if ws.heads[u][i] == nil {
+		ws.heads[u][i] = q
+		q.next = q
+		q.prev = q
+	} else {
+		// Queues are stored in a ring.
+		// Insert the new stream before ws.head, putting it at the end of the list.
+		q.prev = ws.heads[u][i].prev
+		q.next = ws.heads[u][i]
+		q.prev.next = q
+		q.next.prev = q
+	}
+
+	// Update the metadata.
+	ws.streams[streamID] = streamMetadata{
+		location: q,
+		priority: priority,
+	}
+}
+
+func (ws *priorityWriteSchedulerRFC9218) Push(wr FrameWriteRequest) {
+	if wr.isControl() {
+		ws.control.push(wr)
+		return
+	}
+	q := ws.streams[wr.StreamID()].location
+	if q == nil {
+		// This is a closed stream.
+		// wr should not be a HEADERS or DATA frame.
+		// We push the request onto the control queue.
+		if wr.DataSize() > 0 {
+			panic("add DATA on non-open stream")
+		}
+		ws.control.push(wr)
+		return
+	}
+	q.push(wr)
+}
+
+func (ws *priorityWriteSchedulerRFC9218) Pop() (FrameWriteRequest, bool) {
+	// Control and RST_STREAM frames first.
+	if !ws.control.empty() {
+		return ws.control.shift(), true
+	}
+
+	// On the next Pop(), we want to prioritize incremental if we prioritized
+	// non-incremental request of the same urgency this time. Vice-versa.
+	// i.e. when there are incremental and non-incremental requests at the same
+	// priority, we give 50% of our bandwidth to the incremental ones in
+	// aggregate and 50% to the first non-incremental one (since
+	// non-incremental streams do not use round-robin writes).
+	ws.prioritizeIncremental = !ws.prioritizeIncremental
+
+	// Always prioritize lowest u (i.e. highest urgency level).
+	for u := range ws.heads {
+		for i := range ws.heads[u] {
+			// When we want to prioritize incremental, we try to pop i=true
+			// first before i=false when u is the same.
+			if ws.prioritizeIncremental {
+				i = (i + 1) % 2
+			}
+			q := ws.heads[u][i]
+			if q == nil {
+				continue
+			}
+			for {
+				if wr, ok := q.consume(math.MaxInt32); ok {
+					if i == 1 {
+						// For incremental streams, we update head to q.next so
+						// we can round-robin between multiple streams that can
+						// immediately benefit from partial writes.
+						ws.heads[u][i] = q.next
+					} else {
+						// For non-incremental streams, we try to finish one to
+						// completion rather than doing round-robin. However,
+						// we update head here so that if q.consume() is !ok
+						// (e.g. the stream has no more frame to consume), head
+						// is updated to the next q that has frames to consume
+						// on future iterations. This way, we do not prioritize
+						// writing to unavailable stream on next Pop() calls,
+						// preventing head-of-line blocking.
+						ws.heads[u][i] = q
+					}
+					return wr, true
+				}
+				q = q.next
+				if q == ws.heads[u][i] {
+					break
+				}
+			}
+
+		}
+	}
+	return FrameWriteRequest{}, false
+}
@@ -25,7 +25,7 @@ type roundRobinWriteScheduler struct {
 }

 // newRoundRobinWriteScheduler constructs a new write scheduler.
-// The round robin scheduler priorizes control frames
+// The round robin scheduler prioritizes control frames
 // like SETTINGS and PING over DATA frames.
 // When there are no control frames to send, it performs a round-robin
 // selection from the ready streams.
@@ -51,7 +51,7 @@ type EncodeHeadersParam struct {
 	DefaultUserAgent string
 }

-// EncodeHeadersParam is the result of EncodeHeaders.
+// EncodeHeadersResult is the result of EncodeHeaders.
 type EncodeHeadersResult struct {
 	HasBody     bool
 	HasTrailers bool
@@ -399,7 +399,7 @@ type ServerRequestResult struct {

 	// If the request should be rejected, this is a short string suitable for passing
 	// to the http2 package's CountError function.
-	// It might be a bit odd to return errors this way rather than returing an error,
+	// It might be a bit odd to return errors this way rather than returning an error,
 	// but this ensures we don't forget to include a CountError reason.
 	InvalidReason string
 }
@@ -297,7 +297,7 @@ func (up *UsernamePassword) Authenticate(ctx context.Context, rw io.ReadWriter,
 		b = append(b, up.Username...)
 		b = append(b, byte(len(up.Password)))
 		b = append(b, up.Password...)
-		// TODO(mikio): handle IO deadlines and cancelation if
+		// TODO(mikio): handle IO deadlines and cancellation if
 		// necessary
 		if _, err := rw.Write(b); err != nil {
 			return err
@@ -427,13 +427,6 @@ type isolatingRunSequence struct {

 func (i *isolatingRunSequence) Len() int { return len(i.indexes) }

-func maxLevel(a, b level) level {
-	if a > b {
-		return a
-	}
-	return b
-}
-
 // Rule X10, second bullet: Determine the start-of-sequence (sos) and end-of-sequence (eos) types,
 // either L or R, for each isolating run sequence.
 func (p *paragraph) isolatingRunSequence(indexes []int) *isolatingRunSequence {
@@ -474,8 +467,8 @@ func (p *paragraph) isolatingRunSequence(indexes []int) *isolatingRunSequence {
 		indexes: indexes,
 		types:   types,
 		level:   level,
-		sos:     typeForLevel(maxLevel(prevLevel, level)),
-		eos:     typeForLevel(maxLevel(succLevel, level)),
+		sos:     typeForLevel(max(prevLevel, level)),
+		eos:     typeForLevel(max(succLevel, level)),
 	}
 }

@@ -70,6 +70,10 @@
 //	PillAspirin // Aspirin
 //
 // to suppress it in the output.
+//
+// The -trimprefix flag specifies a prefix to remove from the constant names
+// when generating the string representations. For instance, -trimprefix=Pill
+// would be an alternative way to ensure that PillAspirin.String() == "Aspirin".
 package main // import "golang.org/x/tools/cmd/stringer"

 import (
@@ -209,7 +213,7 @@ func main() {
 			// and the separate package of tests (package foo_test).
 			outputName = filepath.Join(dir, baseName(pkg, foundTypes[0]))
 		}
-		err := os.WriteFile(outputName, src, 0644)
+		err := os.WriteFile(outputName, src, 0o644)
 		if err != nil {
 			log.Fatalf("writing output: %s", err)
 		}
@@ -637,44 +641,19 @@ func (g *Generator) buildOneRun(runs [][]Value, typeName string) {
 	values := runs[0]
 	g.Printf("\n")
 	g.declareIndexAndNameVar(values, typeName)
-	// The generated code is simple enough to write as a Printf format.
-	lessThanZero := ""
-	if values[0].signed {
-		lessThanZero = "i < 0 || "
-	}
-	if values[0].value == 0 { // Signed or unsigned, 0 is still 0.
-		g.Printf(stringOneRun, typeName, usize(len(values)), lessThanZero)
-	} else {
-		g.Printf(stringOneRunWithOffset, typeName, values[0].String(), usize(len(values)), lessThanZero)
-	}
+	g.Printf(stringOneRun, typeName, values[0].String())
 }

 // Arguments to format are:
 //
 //	[1]: type name
-//	[2]: size of index element (8 for uint8 etc.)
-//	[3]: less than zero check (for signed types)
+//	[2]: lowest defined value for type, as a string
 const stringOneRun = `func (i %[1]s) String() string {
-	if %[3]si >= %[1]s(len(_%[1]s_index)-1) {
+	idx := int(i) - %[2]s
+	if i < %[2]s || idx >= len(_%[1]s_index)-1 {
 		return "%[1]s(" + strconv.FormatInt(int64(i), 10) + ")"
 	}
-	return _%[1]s_name[_%[1]s_index[i]:_%[1]s_index[i+1]]
-}
-`
-
-// Arguments to format are:
-//	[1]: type name
-//	[2]: lowest defined value for type, as a string
-//	[3]: size of index element (8 for uint8 etc.)
-//	[4]: less than zero check (for signed types)
-/*
- */
-const stringOneRunWithOffset = `func (i %[1]s) String() string {
-	i -= %[2]s
-	if %[4]si >= %[1]s(len(_%[1]s_index)-1) {
-		return "%[1]s(" + strconv.FormatInt(int64(i + %[2]s), 10) + ")"
-	}
-	return _%[1]s_name[_%[1]s_index[i] : _%[1]s_index[i+1]]
+	return _%[1]s_name[_%[1]s_index[idx] : _%[1]s_index[idx+1]]
 }
 `

@@ -0,0 +1,295 @@
+// Copyright 2025 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Package edge defines identifiers for each field of an ast.Node
+// struct type that refers to another Node.
+package edge
+
+import (
+	"fmt"
+	"go/ast"
+	"reflect"
+)
+
+// A Kind describes a field of an ast.Node struct.
+type Kind uint8
+
+// String returns a description of the edge kind.
+func (k Kind) String() string {
+	if k == Invalid {
+		return "<invalid>"
+	}
+	info := fieldInfos[k]
+	return fmt.Sprintf("%v.%s", info.nodeType.Elem().Name(), info.name)
+}
+
+// NodeType returns the pointer-to-struct type of the ast.Node implementation.
+func (k Kind) NodeType() reflect.Type { return fieldInfos[k].nodeType }
+
+// FieldName returns the name of the field.
+func (k Kind) FieldName() string { return fieldInfos[k].name }
+
+// FieldType returns the declared type of the field.
+func (k Kind) FieldType() reflect.Type { return fieldInfos[k].fieldType }
+
+// Get returns the direct child of n identified by (k, idx).
+// n's type must match k.NodeType().
+// idx must be a valid slice index, or -1 for a non-slice.
+func (k Kind) Get(n ast.Node, idx int) ast.Node {
+	if k.NodeType() != reflect.TypeOf(n) {
+		panic(fmt.Sprintf("%v.Get(%T): invalid node type", k, n))
+	}
+	v := reflect.ValueOf(n).Elem().Field(fieldInfos[k].index)
+	if idx != -1 {
+		v = v.Index(idx) // asserts valid index
+	} else {
+		// (The type assertion below asserts that v is not a slice.)
+	}
+	return v.Interface().(ast.Node) // may be nil
+}
+
+const (
+	Invalid Kind = iota // for nodes at the root of the traversal
+
+	// Kinds are sorted alphabetically.
+	// Numbering is not stable.
+	// Each is named Type_Field, where Type is the
+	// ast.Node struct type and Field is the name of the field
+
+	ArrayType_Elt
+	ArrayType_Len
+	AssignStmt_Lhs
+	AssignStmt_Rhs
+	BinaryExpr_X
+	BinaryExpr_Y
+	BlockStmt_List
+	BranchStmt_Label
+	CallExpr_Args
+	CallExpr_Fun
+	CaseClause_Body
+	CaseClause_List
+	ChanType_Value
+	CommClause_Body
+	CommClause_Comm
+	CommentGroup_List
+	CompositeLit_Elts
+	CompositeLit_Type
+	DeclStmt_Decl
+	DeferStmt_Call
+	Ellipsis_Elt
+	ExprStmt_X
+	FieldList_List
+	Field_Comment
+	Field_Doc
+	Field_Names
+	Field_Tag
+	Field_Type
+	File_Decls
+	File_Doc
+	File_Name
+	ForStmt_Body
+	ForStmt_Cond
+	ForStmt_Init
+	ForStmt_Post
+	FuncDecl_Body
+	FuncDecl_Doc
+	FuncDecl_Name
+	FuncDecl_Recv
+	FuncDecl_Type
+	FuncLit_Body
+	FuncLit_Type
+	FuncType_Params
+	FuncType_Results
+	FuncType_TypeParams
+	GenDecl_Doc
+	GenDecl_Specs
+	GoStmt_Call
+	IfStmt_Body
+	IfStmt_Cond
+	IfStmt_Else
+	IfStmt_Init
+	ImportSpec_Comment
+	ImportSpec_Doc
+	ImportSpec_Name
+	ImportSpec_Path
+	IncDecStmt_X
+	IndexExpr_Index
+	IndexExpr_X
+	IndexListExpr_Indices
+	IndexListExpr_X
+	InterfaceType_Methods
+	KeyValueExpr_Key
+	KeyValueExpr_Value
+	LabeledStmt_Label
+	LabeledStmt_Stmt
+	MapType_Key
+	MapType_Value
+	ParenExpr_X
+	RangeStmt_Body
+	RangeStmt_Key
+	RangeStmt_Value
+	RangeStmt_X
+	ReturnStmt_Results
+	SelectStmt_Body
+	SelectorExpr_Sel
+	SelectorExpr_X
+	SendStmt_Chan
+	SendStmt_Value
+	SliceExpr_High
+	SliceExpr_Low
+	SliceExpr_Max
+	SliceExpr_X
+	StarExpr_X
+	StructType_Fields
+	SwitchStmt_Body
+	SwitchStmt_Init
+	SwitchStmt_Tag
+	TypeAssertExpr_Type
+	TypeAssertExpr_X
+	TypeSpec_Comment
+	TypeSpec_Doc
+	TypeSpec_Name
+	TypeSpec_Type
+	TypeSpec_TypeParams
+	TypeSwitchStmt_Assign
+	TypeSwitchStmt_Body
+	TypeSwitchStmt_Init
+	UnaryExpr_X
+	ValueSpec_Comment
+	ValueSpec_Doc
+	ValueSpec_Names
+	ValueSpec_Type
+	ValueSpec_Values
+
+	maxKind
+)
+
+// Assert that the encoding fits in 7 bits,
+// as the inspector relies on this.
+// (We are currently at 104.)
+var _ = [1 << 7]struct{}{}[maxKind]
+
+type fieldInfo struct {
+	nodeType  reflect.Type // pointer-to-struct type of ast.Node implementation
+	name      string
+	index     int
+	fieldType reflect.Type
+}
+
+func info[N ast.Node](fieldName string) fieldInfo {
+	nodePtrType := reflect.TypeFor[N]()
+	f, ok := nodePtrType.Elem().FieldByName(fieldName)
+	if !ok {
+		panic(fieldName)
+	}
+	return fieldInfo{nodePtrType, fieldName, f.Index[0], f.Type}
+}
+
+var fieldInfos = [...]fieldInfo{
+	Invalid:               {},
+	ArrayType_Elt:         info[*ast.ArrayType]("Elt"),
+	ArrayType_Len:         info[*ast.ArrayType]("Len"),
+	AssignStmt_Lhs:        info[*ast.AssignStmt]("Lhs"),
+	AssignStmt_Rhs:        info[*ast.AssignStmt]("Rhs"),
+	BinaryExpr_X:          info[*ast.BinaryExpr]("X"),
+	BinaryExpr_Y:          info[*ast.BinaryExpr]("Y"),
+	BlockStmt_List:        info[*ast.BlockStmt]("List"),
+	BranchStmt_Label:      info[*ast.BranchStmt]("Label"),
+	CallExpr_Args:         info[*ast.CallExpr]("Args"),
+	CallExpr_Fun:          info[*ast.CallExpr]("Fun"),
+	CaseClause_Body:       info[*ast.CaseClause]("Body"),
+	CaseClause_List:       info[*ast.CaseClause]("List"),
+	ChanType_Value:        info[*ast.ChanType]("Value"),
+	CommClause_Body:       info[*ast.CommClause]("Body"),
+	CommClause_Comm:       info[*ast.CommClause]("Comm"),
+	CommentGroup_List:     info[*ast.CommentGroup]("List"),
+	CompositeLit_Elts:     info[*ast.CompositeLit]("Elts"),
+	CompositeLit_Type:     info[*ast.CompositeLit]("Type"),
+	DeclStmt_Decl:         info[*ast.DeclStmt]("Decl"),
+	DeferStmt_Call:        info[*ast.DeferStmt]("Call"),
+	Ellipsis_Elt:          info[*ast.Ellipsis]("Elt"),
+	ExprStmt_X:            info[*ast.ExprStmt]("X"),
+	FieldList_List:        info[*ast.FieldList]("List"),
+	Field_Comment:         info[*ast.Field]("Comment"),
+	Field_Doc:             info[*ast.Field]("Doc"),
+	Field_Names:           info[*ast.Field]("Names"),
+	Field_Tag:             info[*ast.Field]("Tag"),
+	Field_Type:            info[*ast.Field]("Type"),
+	File_Decls:            info[*ast.File]("Decls"),
+	File_Doc:              info[*ast.File]("Doc"),
+	File_Name:             info[*ast.File]("Name"),
+	ForStmt_Body:          info[*ast.ForStmt]("Body"),
+	ForStmt_Cond:          info[*ast.ForStmt]("Cond"),
+	ForStmt_Init:          info[*ast.ForStmt]("Init"),
+	ForStmt_Post:          info[*ast.ForStmt]("Post"),
+	FuncDecl_Body:         info[*ast.FuncDecl]("Body"),
+	FuncDecl_Doc:          info[*ast.FuncDecl]("Doc"),
+	FuncDecl_Name:         info[*ast.FuncDecl]("Name"),
+	FuncDecl_Recv:         info[*ast.FuncDecl]("Recv"),
+	FuncDecl_Type:         info[*ast.FuncDecl]("Type"),
+	FuncLit_Body:          info[*ast.FuncLit]("Body"),
+	FuncLit_Type:          info[*ast.FuncLit]("Type"),
+	FuncType_Params:       info[*ast.FuncType]("Params"),
+	FuncType_Results:      info[*ast.FuncType]("Results"),
+	FuncType_TypeParams:   info[*ast.FuncType]("TypeParams"),
+	GenDecl_Doc:           info[*ast.GenDecl]("Doc"),
+	GenDecl_Specs:         info[*ast.GenDecl]("Specs"),
+	GoStmt_Call:           info[*ast.GoStmt]("Call"),
+	IfStmt_Body:           info[*ast.IfStmt]("Body"),
+	IfStmt_Cond:           info[*ast.IfStmt]("Cond"),
+	IfStmt_Else:           info[*ast.IfStmt]("Else"),
+	IfStmt_Init:           info[*ast.IfStmt]("Init"),
+	ImportSpec_Comment:    info[*ast.ImportSpec]("Comment"),
+	ImportSpec_Doc:        info[*ast.ImportSpec]("Doc"),
+	ImportSpec_Name:       info[*ast.ImportSpec]("Name"),
+	ImportSpec_Path:       info[*ast.ImportSpec]("Path"),
+	IncDecStmt_X:          info[*ast.IncDecStmt]("X"),
+	IndexExpr_Index:       info[*ast.IndexExpr]("Index"),
+	IndexExpr_X:           info[*ast.IndexExpr]("X"),
+	IndexListExpr_Indices: info[*ast.IndexListExpr]("Indices"),
+	IndexListExpr_X:       info[*ast.IndexListExpr]("X"),
+	InterfaceType_Methods: info[*ast.InterfaceType]("Methods"),
+	KeyValueExpr_Key:      info[*ast.KeyValueExpr]("Key"),
+	KeyValueExpr_Value:    info[*ast.KeyValueExpr]("Value"),
+	LabeledStmt_Label:     info[*ast.LabeledStmt]("Label"),
+	LabeledStmt_Stmt:      info[*ast.LabeledStmt]("Stmt"),
+	MapType_Key:           info[*ast.MapType]("Key"),
+	MapType_Value:         info[*ast.MapType]("Value"),
+	ParenExpr_X:           info[*ast.ParenExpr]("X"),
+	RangeStmt_Body:        info[*ast.RangeStmt]("Body"),
+	RangeStmt_Key:         info[*ast.RangeStmt]("Key"),
+	RangeStmt_Value:       info[*ast.RangeStmt]("Value"),
+	RangeStmt_X:           info[*ast.RangeStmt]("X"),
+	ReturnStmt_Results:    info[*ast.ReturnStmt]("Results"),
+	SelectStmt_Body:       info[*ast.SelectStmt]("Body"),
+	SelectorExpr_Sel:      info[*ast.SelectorExpr]("Sel"),
+	SelectorExpr_X:        info[*ast.SelectorExpr]("X"),
+	SendStmt_Chan:         info[*ast.SendStmt]("Chan"),
+	SendStmt_Value:        info[*ast.SendStmt]("Value"),
+	SliceExpr_High:        info[*ast.SliceExpr]("High"),
+	SliceExpr_Low:         info[*ast.SliceExpr]("Low"),
+	SliceExpr_Max:         info[*ast.SliceExpr]("Max"),
+	SliceExpr_X:           info[*ast.SliceExpr]("X"),
+	StarExpr_X:            info[*ast.StarExpr]("X"),
+	StructType_Fields:     info[*ast.StructType]("Fields"),
+	SwitchStmt_Body:       info[*ast.SwitchStmt]("Body"),
+	SwitchStmt_Init:       info[*ast.SwitchStmt]("Init"),
+	SwitchStmt_Tag:        info[*ast.SwitchStmt]("Tag"),
+	TypeAssertExpr_Type:   info[*ast.TypeAssertExpr]("Type"),
+	TypeAssertExpr_X:      info[*ast.TypeAssertExpr]("X"),
+	TypeSpec_Comment:      info[*ast.TypeSpec]("Comment"),
+	TypeSpec_Doc:          info[*ast.TypeSpec]("Doc"),
+	TypeSpec_Name:         info[*ast.TypeSpec]("Name"),
+	TypeSpec_Type:         info[*ast.TypeSpec]("Type"),
+	TypeSpec_TypeParams:   info[*ast.TypeSpec]("TypeParams"),
+	TypeSwitchStmt_Assign: info[*ast.TypeSwitchStmt]("Assign"),
+	TypeSwitchStmt_Body:   info[*ast.TypeSwitchStmt]("Body"),
+	TypeSwitchStmt_Init:   info[*ast.TypeSwitchStmt]("Init"),
+	UnaryExpr_X:           info[*ast.UnaryExpr]("X"),
+	ValueSpec_Comment:     info[*ast.ValueSpec]("Comment"),
+	ValueSpec_Doc:         info[*ast.ValueSpec]("Doc"),
+	ValueSpec_Names:       info[*ast.ValueSpec]("Names"),
+	ValueSpec_Type:        info[*ast.ValueSpec]("Type"),
+	ValueSpec_Values:      info[*ast.ValueSpec]("Values"),
+}
@@ -0,0 +1,502 @@
+// Copyright 2025 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package inspector
+
+import (
+	"fmt"
+	"go/ast"
+	"go/token"
+	"iter"
+	"reflect"
+
+	"golang.org/x/tools/go/ast/edge"
+)
+
+// A Cursor represents an [ast.Node]. It is immutable.
+//
+// Two Cursors compare equal if they represent the same node.
+//
+// Call [Inspector.Root] to obtain a valid cursor for the virtual root
+// node of the traversal.
+//
+// Use the following methods to navigate efficiently around the tree:
+//   - for ancestors, use [Cursor.Parent] and [Cursor.Enclosing];
+//   - for children, use [Cursor.Child], [Cursor.Children],
+//     [Cursor.FirstChild], and [Cursor.LastChild];
+//   - for siblings, use [Cursor.PrevSibling] and [Cursor.NextSibling];
+//   - for descendants, use [Cursor.FindByPos], [Cursor.FindNode],
+//     [Cursor.Inspect], and [Cursor.Preorder].
+//
+// Use the [Cursor.ChildAt] and [Cursor.ParentEdge] methods for
+// information about the edges in a tree: which field (and slice
+// element) of the parent node holds the child.
+type Cursor struct {
+	in    *Inspector
+	index int32 // index of push node; -1 for virtual root node
+}
+
+// Root returns a cursor for the virtual root node,
+// whose children are the files provided to [New].
+//
+// Its [Cursor.Node] method return nil.
+func (in *Inspector) Root() Cursor {
+	return Cursor{in, -1}
+}
+
+// At returns the cursor at the specified index in the traversal,
+// which must have been obtained from [Cursor.Index] on a Cursor
+// belonging to the same Inspector (see [Cursor.Inspector]).
+func (in *Inspector) At(index int32) Cursor {
+	if index < 0 {
+		panic("negative index")
+	}
+	if int(index) >= len(in.events) {
+		panic("index out of range for this inspector")
+	}
+	if in.events[index].index < index {
+		panic("invalid index") // (a push, not a pop)
+	}
+	return Cursor{in, index}
+}
+
+// Inspector returns the cursor's Inspector.
+func (c Cursor) Inspector() *Inspector { return c.in }
+
+// Index returns the index of this cursor position within the package.
+//
+// Clients should not assume anything about the numeric Index value
+// except that it increases monotonically throughout the traversal.
+// It is provided for use with [At].
+//
+// Index must not be called on the Root node.
+func (c Cursor) Index() int32 {
+	if c.index < 0 {
+		panic("Index called on Root node")
+	}
+	return c.index
+}
+
+// Node returns the node at the current cursor position,
+// or nil for the cursor returned by [Inspector.Root].
+func (c Cursor) Node() ast.Node {
+	if c.index < 0 {
+		return nil
+	}
+	return c.in.events[c.index].node
+}
+
+// String returns information about the cursor's node, if any.
+func (c Cursor) String() string {
+	if c.in == nil {
+		return "(invalid)"
+	}
+	if c.index < 0 {
+		return "(root)"
+	}
+	return reflect.TypeOf(c.Node()).String()
+}
+
+// indices return the [start, end) half-open interval of event indices.
+func (c Cursor) indices() (int32, int32) {
+	if c.index < 0 {
+		return 0, int32(len(c.in.events)) // root: all events
+	} else {
+		return c.index, c.in.events[c.index].index + 1 // just one subtree
+	}
+}
+
+// Preorder returns an iterator over the nodes of the subtree
+// represented by c in depth-first order. Each node in the sequence is
+// represented by a Cursor that allows access to the Node, but may
+// also be used to start a new traversal, or to obtain the stack of
+// nodes enclosing the cursor.
+//
+// The traversal sequence is determined by [ast.Inspect]. The types
+// argument, if non-empty, enables type-based filtering of events. The
+// function f if is called only for nodes whose type matches an
+// element of the types slice.
+//
+// If you need control over descent into subtrees,
+// or need both pre- and post-order notifications, use [Cursor.Inspect]
+func (c Cursor) Preorder(types ...ast.Node) iter.Seq[Cursor] {
+	mask := maskOf(types)
+
+	return func(yield func(Cursor) bool) {
+		events := c.in.events
+
+		for i, limit := c.indices(); i < limit; {
+			ev := events[i]
+			if ev.index > i { // push?
+				if ev.typ&mask != 0 && !yield(Cursor{c.in, i}) {
+					break
+				}
+				pop := ev.index
+				if events[pop].typ&mask == 0 {
+					// Subtree does not contain types: skip.
+					i = pop + 1
+					continue
+				}
+			}
+			i++
+		}
+	}
+}
+
+// Inspect visits the nodes of the subtree represented by c in
+// depth-first order. It calls f(n) for each node n before it
+// visits n's children. If f returns true, Inspect invokes f
+// recursively for each of the non-nil children of the node.
+//
+// Each node is represented by a Cursor that allows access to the
+// Node, but may also be used to start a new traversal, or to obtain
+// the stack of nodes enclosing the cursor.
+//
+// The complete traversal sequence is determined by [ast.Inspect].
+// The types argument, if non-empty, enables type-based filtering of
+// events. The function f if is called only for nodes whose type
+// matches an element of the types slice.
+func (c Cursor) Inspect(types []ast.Node, f func(c Cursor) (descend bool)) {
+	mask := maskOf(types)
+	events := c.in.events
+	for i, limit := c.indices(); i < limit; {
+		ev := events[i]
+		if ev.index > i {
+			// push
+			pop := ev.index
+			if ev.typ&mask != 0 && !f(Cursor{c.in, i}) ||
+				events[pop].typ&mask == 0 {
+				// The user opted not to descend, or the
+				// subtree does not contain types:
+				// skip past the pop.
+				i = pop + 1
+				continue
+			}
+		}
+		i++
+	}
+}
+
+// Enclosing returns an iterator over the nodes enclosing the current
+// current node, starting with the Cursor itself.
+//
+// Enclosing must not be called on the Root node (whose [Cursor.Node] returns nil).
+//
+// The types argument, if non-empty, enables type-based filtering of
+// events: the sequence includes only enclosing nodes whose type
+// matches an element of the types slice.
+func (c Cursor) Enclosing(types ...ast.Node) iter.Seq[Cursor] {
+	if c.index < 0 {
+		panic("Cursor.Enclosing called on Root node")
+	}
+
+	mask := maskOf(types)
+
+	return func(yield func(Cursor) bool) {
+		events := c.in.events
+		for i := c.index; i >= 0; i = events[i].parent {
+			if events[i].typ&mask != 0 && !yield(Cursor{c.in, i}) {
+				break
+			}
+		}
+	}
+}
+
+// Parent returns the parent of the current node.
+//
+// Parent must not be called on the Root node (whose [Cursor.Node] returns nil).
+func (c Cursor) Parent() Cursor {
+	if c.index < 0 {
+		panic("Cursor.Parent called on Root node")
+	}
+
+	return Cursor{c.in, c.in.events[c.index].parent}
+}
+
+// ParentEdge returns the identity of the field in the parent node
+// that holds this cursor's node, and if it is a list, the index within it.
+//
+// For example, f(x, y) is a CallExpr whose three children are Idents.
+// f has edge kind [edge.CallExpr_Fun] and index -1.
+// x and y have kind [edge.CallExpr_Args] and indices 0 and 1, respectively.
+//
+// If called on a child of the Root node, it returns ([edge.Invalid], -1).
+//
+// ParentEdge must not be called on the Root node (whose [Cursor.Node] returns nil).
+func (c Cursor) ParentEdge() (edge.Kind, int) {
+	if c.index < 0 {
+		panic("Cursor.ParentEdge called on Root node")
+	}
+	events := c.in.events
+	pop := events[c.index].index
+	return unpackEdgeKindAndIndex(events[pop].parent)
+}
+
+// ChildAt returns the cursor for the child of the
+// current node identified by its edge and index.
+// The index must be -1 if the edge.Kind is not a slice.
+// The indicated child node must exist.
+//
+// ChildAt must not be called on the Root node (whose [Cursor.Node] returns nil).
+//
+// Invariant: c.Parent().ChildAt(c.ParentEdge()) == c.
+func (c Cursor) ChildAt(k edge.Kind, idx int) Cursor {
+	target := packEdgeKindAndIndex(k, idx)
+
+	// Unfortunately there's no shortcut to looping.
+	events := c.in.events
+	i := c.index + 1
+	for {
+		pop := events[i].index
+		if pop < i {
+			break
+		}
+		if events[pop].parent == target {
+			return Cursor{c.in, i}
+		}
+		i = pop + 1
+	}
+	panic(fmt.Sprintf("ChildAt(%v, %d): no such child of %v", k, idx, c))
+}
+
+// Child returns the cursor for n, which must be a direct child of c's Node.
+//
+// Child must not be called on the Root node (whose [Cursor.Node] returns nil).
+func (c Cursor) Child(n ast.Node) Cursor {
+	if c.index < 0 {
+		panic("Cursor.Child called on Root node")
+	}
+
+	if false {
+		// reference implementation
+		for child := range c.Children() {
+			if child.Node() == n {
+				return child
+			}
+		}
+
+	} else {
+		// optimized implementation
+		events := c.in.events
+		for i := c.index + 1; events[i].index > i; i = events[i].index + 1 {
+			if events[i].node == n {
+				return Cursor{c.in, i}
+			}
+		}
+	}
+	panic(fmt.Sprintf("Child(%T): not a child of %v", n, c))
+}
+
+// NextSibling returns the cursor for the next sibling node in the same list
+// (for example, of files, decls, specs, statements, fields, or expressions) as
+// the current node. It returns (zero, false) if the node is the last node in
+// the list, or is not part of a list.
+//
+// NextSibling must not be called on the Root node.
+//
+// See note at [Cursor.Children].
+func (c Cursor) NextSibling() (Cursor, bool) {
+	if c.index < 0 {
+		panic("Cursor.NextSibling called on Root node")
+	}
+
+	events := c.in.events
+	i := events[c.index].index + 1 // after corresponding pop
+	if i < int32(len(events)) {
+		if events[i].index > i { // push?
+			return Cursor{c.in, i}, true
+		}
+	}
+	return Cursor{}, false
+}
+
+// PrevSibling returns the cursor for the previous sibling node in the
+// same list (for example, of files, decls, specs, statements, fields,
+// or expressions) as the current node. It returns zero if the node is
+// the first node in the list, or is not part of a list.
+//
+// It must not be called on the Root node.
+//
+// See note at [Cursor.Children].
+func (c Cursor) PrevSibling() (Cursor, bool) {
+	if c.index < 0 {
+		panic("Cursor.PrevSibling called on Root node")
+	}
+
+	events := c.in.events
+	i := c.index - 1
+	if i >= 0 {
+		if j := events[i].index; j < i { // pop?
+			return Cursor{c.in, j}, true
+		}
+	}
+	return Cursor{}, false
+}
+
+// FirstChild returns the first direct child of the current node,
+// or zero if it has no children.
+func (c Cursor) FirstChild() (Cursor, bool) {
+	events := c.in.events
+	i := c.index + 1                                   // i=0 if c is root
+	if i < int32(len(events)) && events[i].index > i { // push?
+		return Cursor{c.in, i}, true
+	}
+	return Cursor{}, false
+}
+
+// LastChild returns the last direct child of the current node,
+// or zero if it has no children.
+func (c Cursor) LastChild() (Cursor, bool) {
+	events := c.in.events
+	if c.index < 0 { // root?
+		if len(events) > 0 {
+			// return push of final event (a pop)
+			return Cursor{c.in, events[len(events)-1].index}, true
+		}
+	} else {
+		j := events[c.index].index - 1 // before corresponding pop
+		// Inv: j == c.index if c has no children
+		//  or  j is last child's pop.
+		if j > c.index { // c has children
+			return Cursor{c.in, events[j].index}, true
+		}
+	}
+	return Cursor{}, false
+}
+
+// Children returns an iterator over the direct children of the
+// current node, if any.
+//
+// When using Children, NextChild, and PrevChild, bear in mind that a
+// Node's children may come from different fields, some of which may
+// be lists of nodes without a distinguished intervening container
+// such as [ast.BlockStmt].
+//
+// For example, [ast.CaseClause] has a field List of expressions and a
+// field Body of statements, so the children of a CaseClause are a mix
+// of expressions and statements. Other nodes that have "uncontained"
+// list fields include:
+//
+//   - [ast.ValueSpec] (Names, Values)
+//   - [ast.CompositeLit] (Type, Elts)
+//   - [ast.IndexListExpr] (X, Indices)
+//   - [ast.CallExpr] (Fun, Args)
+//   - [ast.AssignStmt] (Lhs, Rhs)
+//
+// So, do not assume that the previous sibling of an ast.Stmt is also
+// an ast.Stmt, or if it is, that they are executed sequentially,
+// unless you have established that, say, its parent is a BlockStmt
+// or its [Cursor.ParentEdge] is [edge.BlockStmt_List].
+// For example, given "for S1; ; S2 {}", the predecessor of S2 is S1,
+// even though they are not executed in sequence.
+func (c Cursor) Children() iter.Seq[Cursor] {
+	return func(yield func(Cursor) bool) {
+		c, ok := c.FirstChild()
+		for ok && yield(c) {
+			c, ok = c.NextSibling()
+		}
+	}
+}
+
+// Contains reports whether c contains or is equal to c2.
+//
+// Both Cursors must belong to the same [Inspector];
+// neither may be its Root node.
+func (c Cursor) Contains(c2 Cursor) bool {
+	if c.in != c2.in {
+		panic("different inspectors")
+	}
+	events := c.in.events
+	return c.index <= c2.index && events[c2.index].index <= events[c.index].index
+}
+
+// FindNode returns the cursor for node n if it belongs to the subtree
+// rooted at c. It returns zero if n is not found.
+func (c Cursor) FindNode(n ast.Node) (Cursor, bool) {
+
+	// FindNode is equivalent to this code,
+	// but more convenient and 15-20% faster:
+	if false {
+		for candidate := range c.Preorder(n) {
+			if candidate.Node() == n {
+				return candidate, true
+			}
+		}
+		return Cursor{}, false
+	}
+
+	// TODO(adonovan): opt: should we assume Node.Pos is accurate
+	// and combine type-based filtering with position filtering
+	// like FindByPos?
+
+	mask := maskOf([]ast.Node{n})
+	events := c.in.events
+
+	for i, limit := c.indices(); i < limit; i++ {
+		ev := events[i]
+		if ev.index > i { // push?
+			if ev.typ&mask != 0 && ev.node == n {
+				return Cursor{c.in, i}, true
+			}
+			pop := ev.index
+			if events[pop].typ&mask == 0 {
+				// Subtree does not contain type of n: skip.
+				i = pop
+			}
+		}
+	}
+	return Cursor{}, false
+}
+
+// FindByPos returns the cursor for the innermost node n in the tree
+// rooted at c such that n.Pos() <= start && end <= n.End().
+// (For an *ast.File, it uses the bounds n.FileStart-n.FileEnd.)
+//
+// It returns zero if none is found.
+// Precondition: start <= end.
+//
+// See also [astutil.PathEnclosingInterval], which
+// tolerates adjoining whitespace.
+func (c Cursor) FindByPos(start, end token.Pos) (Cursor, bool) {
+	if end < start {
+		panic("end < start")
+	}
+	events := c.in.events
+
+	// This algorithm could be implemented using c.Inspect,
+	// but it is about 2.5x slower.
+
+	best := int32(-1) // push index of latest (=innermost) node containing range
+	for i, limit := c.indices(); i < limit; i++ {
+		ev := events[i]
+		if ev.index > i { // push?
+			n := ev.node
+			var nodeEnd token.Pos
+			if file, ok := n.(*ast.File); ok {
+				nodeEnd = file.FileEnd
+				// Note: files may be out of Pos order.
+				if file.FileStart > start {
+					i = ev.index // disjoint, after; skip to next file
+					continue
+				}
+			} else {
+				nodeEnd = n.End()
+				if n.Pos() > start {
+					break // disjoint, after; stop
+				}
+			}
+			// Inv: node.{Pos,FileStart} <= start
+			if end <= nodeEnd {
+				// node fully contains target range
+				best = i
+			} else if nodeEnd < start {
+				i = ev.index // disjoint, before; skip forward
+			}
+		}
+	}
+	if best >= 0 {
+		return Cursor{c.in, best}, true
+	}
+	return Cursor{}, false
+}
@@ -0,0 +1,311 @@
+// Copyright 2018 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Package inspector provides helper functions for traversal over the
+// syntax trees of a package, including node filtering by type, and
+// materialization of the traversal stack.
+//
+// During construction, the inspector does a complete traversal and
+// builds a list of push/pop events and their node type. Subsequent
+// method calls that request a traversal scan this list, rather than walk
+// the AST, and perform type filtering using efficient bit sets.
+// This representation is sometimes called a "balanced parenthesis tree."
+//
+// Experiments suggest the inspector's traversals are about 2.5x faster
+// than [ast.Inspect], but it may take around 5 traversals for this
+// benefit to amortize the inspector's construction cost.
+// If efficiency is the primary concern, do not use Inspector for
+// one-off traversals.
+//
+// The [Cursor] type provides a more flexible API for efficient
+// navigation of syntax trees in all four "cardinal directions". For
+// example, traversals may be nested, so you can find each node of
+// type A and then search within it for nodes of type B. Or you can
+// traverse from a node to its immediate neighbors: its parent, its
+// previous and next sibling, or its first and last child. We
+// recommend using methods of Cursor in preference to Inspector where
+// possible.
+package inspector
+
+// There are four orthogonal features in a traversal:
+//  1 type filtering
+//  2 pruning
+//  3 postorder calls to f
+//  4 stack
+// Rather than offer all of them in the API,
+// only a few combinations are exposed:
+// - Preorder is the fastest and has fewest features,
+//   but is the most commonly needed traversal.
+// - Nodes and WithStack both provide pruning and postorder calls,
+//   even though few clients need it, because supporting two versions
+//   is not justified.
+// More combinations could be supported by expressing them as
+// wrappers around a more generic traversal, but this was measured
+// and found to degrade performance significantly (30%).
+
+import (
+	"go/ast"
+
+	"golang.org/x/tools/go/ast/edge"
+)
+
+// An Inspector provides methods for inspecting
+// (traversing) the syntax trees of a package.
+type Inspector struct {
+	events []event
+}
+
+func packEdgeKindAndIndex(ek edge.Kind, index int) int32 {
+	return int32(uint32(index+1)<<7 | uint32(ek))
+}
+
+// unpackEdgeKindAndIndex unpacks the edge kind and edge index (within
+// an []ast.Node slice) from the parent field of a pop event.
+func unpackEdgeKindAndIndex(x int32) (edge.Kind, int) {
+	// The "parent" field of a pop node holds the
+	// edge Kind in the lower 7 bits and the index+1
+	// in the upper 25.
+	return edge.Kind(x & 0x7f), int(x>>7) - 1
+}
+
+// New returns an Inspector for the specified syntax trees.
+func New(files []*ast.File) *Inspector {
+	return &Inspector{traverse(files)}
+}
+
+// An event represents a push or a pop
+// of an ast.Node during a traversal.
+type event struct {
+	node   ast.Node
+	typ    uint64 // typeOf(node) on push event, or union of typ strictly between push and pop events on pop events
+	index  int32  // index of corresponding push or pop event
+	parent int32  // index of parent's push node (push nodes only), or packed edge kind/index (pop nodes only)
+}
+
+// TODO: Experiment with storing only the second word of event.node (unsafe.Pointer).
+// Type can be recovered from the sole bit in typ.
+// [Tried this, wasn't faster. --adonovan]
+
+// Preorder visits all the nodes of the files supplied to New in
+// depth-first order. It calls f(n) for each node n before it visits
+// n's children.
+//
+// The complete traversal sequence is determined by [ast.Inspect].
+// The types argument, if non-empty, enables type-based filtering of
+// events. The function f is called only for nodes whose type
+// matches an element of the types slice.
+//
+// The [Cursor.Preorder] method provides a richer alternative interface.
+// Example:
+//
+//	for c := range in.Root().Preorder(types) { ... }
+func (in *Inspector) Preorder(types []ast.Node, f func(ast.Node)) {
+	// Because it avoids postorder calls to f, and the pruning
+	// check, Preorder is almost twice as fast as Nodes. The two
+	// features seem to contribute similar slowdowns (~1.4x each).
+
+	// This function is equivalent to the PreorderSeq call below,
+	// but to avoid the additional dynamic call (which adds 13-35%
+	// to the benchmarks), we expand it out.
+	//
+	// in.PreorderSeq(types...)(func(n ast.Node) bool {
+	// 	f(n)
+	// 	return true
+	// })
+
+	mask := maskOf(types)
+	for i := int32(0); i < int32(len(in.events)); {
+		ev := in.events[i]
+		if ev.index > i {
+			// push
+			if ev.typ&mask != 0 {
+				f(ev.node)
+			}
+			pop := ev.index
+			if in.events[pop].typ&mask == 0 {
+				// Subtrees do not contain types: skip them and pop.
+				i = pop + 1
+				continue
+			}
+		}
+		i++
+	}
+}
+
+// Nodes visits the nodes of the files supplied to New in depth-first
+// order. It calls f(n, true) for each node n before it visits n's
+// children. If f returns true, Nodes invokes f recursively for each
+// of the non-nil children of the node, followed by a call of
+// f(n, false).
+//
+// The complete traversal sequence is determined by [ast.Inspect].
+// The types argument, if non-empty, enables type-based filtering of
+// events. The function f if is called only for nodes whose type
+// matches an element of the types slice.
+//
+// The [Cursor.Inspect] method provides a richer alternative interface.
+// Example:
+//
+//	in.Root().Inspect(types, func(c Cursor) bool {
+//		...
+//		return true
+//	}
+func (in *Inspector) Nodes(types []ast.Node, f func(n ast.Node, push bool) (proceed bool)) {
+	mask := maskOf(types)
+	for i := int32(0); i < int32(len(in.events)); {
+		ev := in.events[i]
+		if ev.index > i {
+			// push
+			pop := ev.index
+			if ev.typ&mask != 0 {
+				if !f(ev.node, true) {
+					i = pop + 1 // jump to corresponding pop + 1
+					continue
+				}
+			}
+			if in.events[pop].typ&mask == 0 {
+				// Subtrees do not contain types: skip them.
+				i = pop
+				continue
+			}
+		} else {
+			// pop
+			push := ev.index
+			if in.events[push].typ&mask != 0 {
+				f(ev.node, false)
+			}
+		}
+		i++
+	}
+}
+
+// WithStack visits nodes in a similar manner to Nodes, but it
+// supplies each call to f an additional argument, the current
+// traversal stack. The stack's first element is the outermost node,
+// an *ast.File; its last is the innermost, n.
+//
+// The [Cursor.Inspect] method provides a richer alternative interface.
+// Example:
+//
+//	in.Root().Inspect(types, func(c Cursor) bool {
+//		stack := slices.Collect(c.Enclosing())
+//		...
+//		return true
+//	})
+func (in *Inspector) WithStack(types []ast.Node, f func(n ast.Node, push bool, stack []ast.Node) (proceed bool)) {
+	mask := maskOf(types)
+	var stack []ast.Node
+	for i := int32(0); i < int32(len(in.events)); {
+		ev := in.events[i]
+		if ev.index > i {
+			// push
+			pop := ev.index
+			stack = append(stack, ev.node)
+			if ev.typ&mask != 0 {
+				if !f(ev.node, true, stack) {
+					i = pop + 1
+					stack = stack[:len(stack)-1]
+					continue
+				}
+			}
+			if in.events[pop].typ&mask == 0 {
+				// Subtrees does not contain types: skip them.
+				i = pop
+				continue
+			}
+		} else {
+			// pop
+			push := ev.index
+			if in.events[push].typ&mask != 0 {
+				f(ev.node, false, stack)
+			}
+			stack = stack[:len(stack)-1]
+		}
+		i++
+	}
+}
+
+// traverse builds the table of events representing a traversal.
+func traverse(files []*ast.File) []event {
+	// Preallocate approximate number of events
+	// based on source file extent of the declarations.
+	// (We use End-Pos not FileStart-FileEnd to neglect
+	// the effect of long doc comments.)
+	// This makes traverse faster by 4x (!).
+	var extent int
+	for _, f := range files {
+		extent += int(f.End() - f.Pos())
+	}
+	// This estimate is based on the net/http package.
+	capacity := min(extent*33/100, 1e6) // impose some reasonable maximum (1M)
+
+	v := &visitor{
+		events: make([]event, 0, capacity),
+		stack:  []item{{index: -1}}, // include an extra event so file nodes have a parent
+	}
+	for _, file := range files {
+		walk(v, edge.Invalid, -1, file)
+	}
+	return v.events
+}
+
+type visitor struct {
+	events []event
+	stack  []item
+}
+
+type item struct {
+	index            int32  // index of current node's push event
+	parentIndex      int32  // index of parent node's push event
+	typAccum         uint64 // accumulated type bits of current node's descendants
+	edgeKindAndIndex int32  // edge.Kind and index, bit packed
+}
+
+func (v *visitor) push(ek edge.Kind, eindex int, node ast.Node) {
+	var (
+		index       = int32(len(v.events))
+		parentIndex = v.stack[len(v.stack)-1].index
+	)
+	v.events = append(v.events, event{
+		node:   node,
+		parent: parentIndex,
+		typ:    typeOf(node),
+		index:  0, // (pop index is set later by visitor.pop)
+	})
+	v.stack = append(v.stack, item{
+		index:            index,
+		parentIndex:      parentIndex,
+		edgeKindAndIndex: packEdgeKindAndIndex(ek, eindex),
+	})
+
+	// 2B nodes ought to be enough for anyone!
+	if int32(len(v.events)) < 0 {
+		panic("event index exceeded int32")
+	}
+
+	// 32M elements in an []ast.Node ought to be enough for anyone!
+	if ek2, eindex2 := unpackEdgeKindAndIndex(packEdgeKindAndIndex(ek, eindex)); ek2 != ek || eindex2 != eindex {
+		panic("Node slice index exceeded uint25")
+	}
+}
+
+func (v *visitor) pop(node ast.Node) {
+	top := len(v.stack) - 1
+	current := v.stack[top]
+
+	push := &v.events[current.index]
+	parent := &v.stack[top-1]
+
+	push.index = int32(len(v.events))              // make push event refer to pop
+	parent.typAccum |= current.typAccum | push.typ // accumulate type bits into parent
+
+	v.stack = v.stack[:top]
+
+	v.events = append(v.events, event{
+		node:   node,
+		typ:    current.typAccum,
+		index:  current.index,
+		parent: current.edgeKindAndIndex, // see [unpackEdgeKindAndIndex]
+	})
+}
@@ -0,0 +1,85 @@
+// Copyright 2024 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+//go:build go1.23
+
+package inspector
+
+import (
+	"go/ast"
+	"iter"
+)
+
+// PreorderSeq returns an iterator that visits all the
+// nodes of the files supplied to New in depth-first order.
+// It visits each node n before n's children.
+// The complete traversal sequence is determined by ast.Inspect.
+//
+// The types argument, if non-empty, enables type-based
+// filtering of events: only nodes whose type matches an
+// element of the types slice are included in the sequence.
+func (in *Inspector) PreorderSeq(types ...ast.Node) iter.Seq[ast.Node] {
+
+	// This implementation is identical to Preorder,
+	// except that it supports breaking out of the loop.
+
+	return func(yield func(ast.Node) bool) {
+		mask := maskOf(types)
+		for i := int32(0); i < int32(len(in.events)); {
+			ev := in.events[i]
+			if ev.index > i {
+				// push
+				if ev.typ&mask != 0 {
+					if !yield(ev.node) {
+						break
+					}
+				}
+				pop := ev.index
+				if in.events[pop].typ&mask == 0 {
+					// Subtrees do not contain types: skip them and pop.
+					i = pop + 1
+					continue
+				}
+			}
+			i++
+		}
+	}
+}
+
+// All[N] returns an iterator over all the nodes of type N.
+// N must be a pointer-to-struct type that implements ast.Node.
+//
+// Example:
+//
+//	for call := range All[*ast.CallExpr](in) { ... }
+func All[N interface {
+	*S
+	ast.Node
+}, S any](in *Inspector) iter.Seq[N] {
+
+	// To avoid additional dynamic call overheads,
+	// we duplicate rather than call the logic of PreorderSeq.
+
+	mask := typeOf((N)(nil))
+	return func(yield func(N) bool) {
+		for i := int32(0); i < int32(len(in.events)); {
+			ev := in.events[i]
+			if ev.index > i {
+				// push
+				if ev.typ&mask != 0 {
+					if !yield(ev.node.(N)) {
+						break
+					}
+				}
+				pop := ev.index
+				if in.events[pop].typ&mask == 0 {
+					// Subtrees do not contain types: skip them and pop.
+					i = pop + 1
+					continue
+				}
+			}
+			i++
+		}
+	}
+}
@@ -0,0 +1,227 @@
+// Copyright 2018 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package inspector
+
+// This file defines func typeOf(ast.Node) uint64.
+//
+// The initial map-based implementation was too slow;
+// see https://go-review.googlesource.com/c/tools/+/135655/1/go/ast/inspector/inspector.go#196
+
+import (
+	"go/ast"
+	"math"
+)
+
+const (
+	nArrayType = iota
+	nAssignStmt
+	nBadDecl
+	nBadExpr
+	nBadStmt
+	nBasicLit
+	nBinaryExpr
+	nBlockStmt
+	nBranchStmt
+	nCallExpr
+	nCaseClause
+	nChanType
+	nCommClause
+	nComment
+	nCommentGroup
+	nCompositeLit
+	nDeclStmt
+	nDeferStmt
+	nEllipsis
+	nEmptyStmt
+	nExprStmt
+	nField
+	nFieldList
+	nFile
+	nForStmt
+	nFuncDecl
+	nFuncLit
+	nFuncType
+	nGenDecl
+	nGoStmt
+	nIdent
+	nIfStmt
+	nImportSpec
+	nIncDecStmt
+	nIndexExpr
+	nIndexListExpr
+	nInterfaceType
+	nKeyValueExpr
+	nLabeledStmt
+	nMapType
+	nPackage
+	nParenExpr
+	nRangeStmt
+	nReturnStmt
+	nSelectStmt
+	nSelectorExpr
+	nSendStmt
+	nSliceExpr
+	nStarExpr
+	nStructType
+	nSwitchStmt
+	nTypeAssertExpr
+	nTypeSpec
+	nTypeSwitchStmt
+	nUnaryExpr
+	nValueSpec
+)
+
+// typeOf returns a distinct single-bit value that represents the type of n.
+//
+// Various implementations were benchmarked with BenchmarkNewInspector:
+//
+//	                                                                GOGC=off
+//	- type switch					4.9-5.5ms	2.1ms
+//	- binary search over a sorted list of types	5.5-5.9ms	2.5ms
+//	- linear scan, frequency-ordered list		5.9-6.1ms	2.7ms
+//	- linear scan, unordered list			6.4ms		2.7ms
+//	- hash table					6.5ms		3.1ms
+//
+// A perfect hash seemed like overkill.
+//
+// The compiler's switch statement is the clear winner
+// as it produces a binary tree in code,
+// with constant conditions and good branch prediction.
+// (Sadly it is the most verbose in source code.)
+// Binary search suffered from poor branch prediction.
+func typeOf(n ast.Node) uint64 {
+	// Fast path: nearly half of all nodes are identifiers.
+	if _, ok := n.(*ast.Ident); ok {
+		return 1 << nIdent
+	}
+
+	// These cases include all nodes encountered by ast.Inspect.
+	switch n.(type) {
+	case *ast.ArrayType:
+		return 1 << nArrayType
+	case *ast.AssignStmt:
+		return 1 << nAssignStmt
+	case *ast.BadDecl:
+		return 1 << nBadDecl
+	case *ast.BadExpr:
+		return 1 << nBadExpr
+	case *ast.BadStmt:
+		return 1 << nBadStmt
+	case *ast.BasicLit:
+		return 1 << nBasicLit
+	case *ast.BinaryExpr:
+		return 1 << nBinaryExpr
+	case *ast.BlockStmt:
+		return 1 << nBlockStmt
+	case *ast.BranchStmt:
+		return 1 << nBranchStmt
+	case *ast.CallExpr:
+		return 1 << nCallExpr
+	case *ast.CaseClause:
+		return 1 << nCaseClause
+	case *ast.ChanType:
+		return 1 << nChanType
+	case *ast.CommClause:
+		return 1 << nCommClause
+	case *ast.Comment:
+		return 1 << nComment
+	case *ast.CommentGroup:
+		return 1 << nCommentGroup
+	case *ast.CompositeLit:
+		return 1 << nCompositeLit
+	case *ast.DeclStmt:
+		return 1 << nDeclStmt
+	case *ast.DeferStmt:
+		return 1 << nDeferStmt
+	case *ast.Ellipsis:
+		return 1 << nEllipsis
+	case *ast.EmptyStmt:
+		return 1 << nEmptyStmt
+	case *ast.ExprStmt:
+		return 1 << nExprStmt
+	case *ast.Field:
+		return 1 << nField
+	case *ast.FieldList:
+		return 1 << nFieldList
+	case *ast.File:
+		return 1 << nFile
+	case *ast.ForStmt:
+		return 1 << nForStmt
+	case *ast.FuncDecl:
+		return 1 << nFuncDecl
+	case *ast.FuncLit:
+		return 1 << nFuncLit
+	case *ast.FuncType:
+		return 1 << nFuncType
+	case *ast.GenDecl:
+		return 1 << nGenDecl
+	case *ast.GoStmt:
+		return 1 << nGoStmt
+	case *ast.Ident:
+		return 1 << nIdent
+	case *ast.IfStmt:
+		return 1 << nIfStmt
+	case *ast.ImportSpec:
+		return 1 << nImportSpec
+	case *ast.IncDecStmt:
+		return 1 << nIncDecStmt
+	case *ast.IndexExpr:
+		return 1 << nIndexExpr
+	case *ast.IndexListExpr:
+		return 1 << nIndexListExpr
+	case *ast.InterfaceType:
+		return 1 << nInterfaceType
+	case *ast.KeyValueExpr:
+		return 1 << nKeyValueExpr
+	case *ast.LabeledStmt:
+		return 1 << nLabeledStmt
+	case *ast.MapType:
+		return 1 << nMapType
+	case *ast.Package:
+		return 1 << nPackage
+	case *ast.ParenExpr:
+		return 1 << nParenExpr
+	case *ast.RangeStmt:
+		return 1 << nRangeStmt
+	case *ast.ReturnStmt:
+		return 1 << nReturnStmt
+	case *ast.SelectStmt:
+		return 1 << nSelectStmt
+	case *ast.SelectorExpr:
+		return 1 << nSelectorExpr
+	case *ast.SendStmt:
+		return 1 << nSendStmt
+	case *ast.SliceExpr:
+		return 1 << nSliceExpr
+	case *ast.StarExpr:
+		return 1 << nStarExpr
+	case *ast.StructType:
+		return 1 << nStructType
+	case *ast.SwitchStmt:
+		return 1 << nSwitchStmt
+	case *ast.TypeAssertExpr:
+		return 1 << nTypeAssertExpr
+	case *ast.TypeSpec:
+		return 1 << nTypeSpec
+	case *ast.TypeSwitchStmt:
+		return 1 << nTypeSwitchStmt
+	case *ast.UnaryExpr:
+		return 1 << nUnaryExpr
+	case *ast.ValueSpec:
+		return 1 << nValueSpec
+	}
+	return 0
+}
+
+func maskOf(nodes []ast.Node) uint64 {
+	if len(nodes) == 0 {
+		return math.MaxUint64 // match all node types
+	}
+	var mask uint64
+	for _, n := range nodes {
+		mask |= typeOf(n)
+	}
+	return mask
+}
@@ -0,0 +1,341 @@
+// Copyright 2025 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package inspector
+
+// This file is a fork of ast.Inspect to reduce unnecessary dynamic
+// calls and to gather edge information.
+//
+// Consistency with the original is ensured by TestInspectAllNodes.
+
+import (
+	"fmt"
+	"go/ast"
+
+	"golang.org/x/tools/go/ast/edge"
+)
+
+func walkList[N ast.Node](v *visitor, ek edge.Kind, list []N) {
+	for i, node := range list {
+		walk(v, ek, i, node)
+	}
+}
+
+func walk(v *visitor, ek edge.Kind, index int, node ast.Node) {
+	v.push(ek, index, node)
+
+	// walk children
+	// (the order of the cases matches the order
+	// of the corresponding node types in ast.go)
+	switch n := node.(type) {
+	// Comments and fields
+	case *ast.Comment:
+		// nothing to do
+
+	case *ast.CommentGroup:
+		walkList(v, edge.CommentGroup_List, n.List)
+
+	case *ast.Field:
+		if n.Doc != nil {
+			walk(v, edge.Field_Doc, -1, n.Doc)
+		}
+		walkList(v, edge.Field_Names, n.Names)
+		if n.Type != nil {
+			walk(v, edge.Field_Type, -1, n.Type)
+		}
+		if n.Tag != nil {
+			walk(v, edge.Field_Tag, -1, n.Tag)
+		}
+		if n.Comment != nil {
+			walk(v, edge.Field_Comment, -1, n.Comment)
+		}
+
+	case *ast.FieldList:
+		walkList(v, edge.FieldList_List, n.List)
+
+	// Expressions
+	case *ast.BadExpr, *ast.Ident, *ast.BasicLit:
+		// nothing to do
+
+	case *ast.Ellipsis:
+		if n.Elt != nil {
+			walk(v, edge.Ellipsis_Elt, -1, n.Elt)
+		}
+
+	case *ast.FuncLit:
+		walk(v, edge.FuncLit_Type, -1, n.Type)
+		walk(v, edge.FuncLit_Body, -1, n.Body)
+
+	case *ast.CompositeLit:
+		if n.Type != nil {
+			walk(v, edge.CompositeLit_Type, -1, n.Type)
+		}
+		walkList(v, edge.CompositeLit_Elts, n.Elts)
+
+	case *ast.ParenExpr:
+		walk(v, edge.ParenExpr_X, -1, n.X)
+
+	case *ast.SelectorExpr:
+		walk(v, edge.SelectorExpr_X, -1, n.X)
+		walk(v, edge.SelectorExpr_Sel, -1, n.Sel)
+
+	case *ast.IndexExpr:
+		walk(v, edge.IndexExpr_X, -1, n.X)
+		walk(v, edge.IndexExpr_Index, -1, n.Index)
+
+	case *ast.IndexListExpr:
+		walk(v, edge.IndexListExpr_X, -1, n.X)
+		walkList(v, edge.IndexListExpr_Indices, n.Indices)
+
+	case *ast.SliceExpr:
+		walk(v, edge.SliceExpr_X, -1, n.X)
+		if n.Low != nil {
+			walk(v, edge.SliceExpr_Low, -1, n.Low)
+		}
+		if n.High != nil {
+			walk(v, edge.SliceExpr_High, -1, n.High)
+		}
+		if n.Max != nil {
+			walk(v, edge.SliceExpr_Max, -1, n.Max)
+		}
+
+	case *ast.TypeAssertExpr:
+		walk(v, edge.TypeAssertExpr_X, -1, n.X)
+		if n.Type != nil {
+			walk(v, edge.TypeAssertExpr_Type, -1, n.Type)
+		}
+
+	case *ast.CallExpr:
+		walk(v, edge.CallExpr_Fun, -1, n.Fun)
+		walkList(v, edge.CallExpr_Args, n.Args)
+
+	case *ast.StarExpr:
+		walk(v, edge.StarExpr_X, -1, n.X)
+
+	case *ast.UnaryExpr:
+		walk(v, edge.UnaryExpr_X, -1, n.X)
+
+	case *ast.BinaryExpr:
+		walk(v, edge.BinaryExpr_X, -1, n.X)
+		walk(v, edge.BinaryExpr_Y, -1, n.Y)
+
+	case *ast.KeyValueExpr:
+		walk(v, edge.KeyValueExpr_Key, -1, n.Key)
+		walk(v, edge.KeyValueExpr_Value, -1, n.Value)
+
+	// Types
+	case *ast.ArrayType:
+		if n.Len != nil {
+			walk(v, edge.ArrayType_Len, -1, n.Len)
+		}
+		walk(v, edge.ArrayType_Elt, -1, n.Elt)
+
+	case *ast.StructType:
+		walk(v, edge.StructType_Fields, -1, n.Fields)
+
+	case *ast.FuncType:
+		if n.TypeParams != nil {
+			walk(v, edge.FuncType_TypeParams, -1, n.TypeParams)
+		}
+		if n.Params != nil {
+			walk(v, edge.FuncType_Params, -1, n.Params)
+		}
+		if n.Results != nil {
+			walk(v, edge.FuncType_Results, -1, n.Results)
+		}
+
+	case *ast.InterfaceType:
+		walk(v, edge.InterfaceType_Methods, -1, n.Methods)
+
+	case *ast.MapType:
+		walk(v, edge.MapType_Key, -1, n.Key)
+		walk(v, edge.MapType_Value, -1, n.Value)
+
+	case *ast.ChanType:
+		walk(v, edge.ChanType_Value, -1, n.Value)
+
+	// Statements
+	case *ast.BadStmt:
+		// nothing to do
+
+	case *ast.DeclStmt:
+		walk(v, edge.DeclStmt_Decl, -1, n.Decl)
+
+	case *ast.EmptyStmt:
+		// nothing to do
+
+	case *ast.LabeledStmt:
+		walk(v, edge.LabeledStmt_Label, -1, n.Label)
+		walk(v, edge.LabeledStmt_Stmt, -1, n.Stmt)
+
+	case *ast.ExprStmt:
+		walk(v, edge.ExprStmt_X, -1, n.X)
+
+	case *ast.SendStmt:
+		walk(v, edge.SendStmt_Chan, -1, n.Chan)
+		walk(v, edge.SendStmt_Value, -1, n.Value)
+
+	case *ast.IncDecStmt:
+		walk(v, edge.IncDecStmt_X, -1, n.X)
+
+	case *ast.AssignStmt:
+		walkList(v, edge.AssignStmt_Lhs, n.Lhs)
+		walkList(v, edge.AssignStmt_Rhs, n.Rhs)
+
+	case *ast.GoStmt:
+		walk(v, edge.GoStmt_Call, -1, n.Call)
+
+	case *ast.DeferStmt:
+		walk(v, edge.DeferStmt_Call, -1, n.Call)
+
+	case *ast.ReturnStmt:
+		walkList(v, edge.ReturnStmt_Results, n.Results)
+
+	case *ast.BranchStmt:
+		if n.Label != nil {
+			walk(v, edge.BranchStmt_Label, -1, n.Label)
+		}
+
+	case *ast.BlockStmt:
+		walkList(v, edge.BlockStmt_List, n.List)
+
+	case *ast.IfStmt:
+		if n.Init != nil {
+			walk(v, edge.IfStmt_Init, -1, n.Init)
+		}
+		walk(v, edge.IfStmt_Cond, -1, n.Cond)
+		walk(v, edge.IfStmt_Body, -1, n.Body)
+		if n.Else != nil {
+			walk(v, edge.IfStmt_Else, -1, n.Else)
+		}
+
+	case *ast.CaseClause:
+		walkList(v, edge.CaseClause_List, n.List)
+		walkList(v, edge.CaseClause_Body, n.Body)
+
+	case *ast.SwitchStmt:
+		if n.Init != nil {
+			walk(v, edge.SwitchStmt_Init, -1, n.Init)
+		}
+		if n.Tag != nil {
+			walk(v, edge.SwitchStmt_Tag, -1, n.Tag)
+		}
+		walk(v, edge.SwitchStmt_Body, -1, n.Body)
+
+	case *ast.TypeSwitchStmt:
+		if n.Init != nil {
+			walk(v, edge.TypeSwitchStmt_Init, -1, n.Init)
+		}
+		walk(v, edge.TypeSwitchStmt_Assign, -1, n.Assign)
+		walk(v, edge.TypeSwitchStmt_Body, -1, n.Body)
+
+	case *ast.CommClause:
+		if n.Comm != nil {
+			walk(v, edge.CommClause_Comm, -1, n.Comm)
+		}
+		walkList(v, edge.CommClause_Body, n.Body)
+
+	case *ast.SelectStmt:
+		walk(v, edge.SelectStmt_Body, -1, n.Body)
+
+	case *ast.ForStmt:
+		if n.Init != nil {
+			walk(v, edge.ForStmt_Init, -1, n.Init)
+		}
+		if n.Cond != nil {
+			walk(v, edge.ForStmt_Cond, -1, n.Cond)
+		}
+		if n.Post != nil {
+			walk(v, edge.ForStmt_Post, -1, n.Post)
+		}
+		walk(v, edge.ForStmt_Body, -1, n.Body)
+
+	case *ast.RangeStmt:
+		if n.Key != nil {
+			walk(v, edge.RangeStmt_Key, -1, n.Key)
+		}
+		if n.Value != nil {
+			walk(v, edge.RangeStmt_Value, -1, n.Value)
+		}
+		walk(v, edge.RangeStmt_X, -1, n.X)
+		walk(v, edge.RangeStmt_Body, -1, n.Body)
+
+	// Declarations
+	case *ast.ImportSpec:
+		if n.Doc != nil {
+			walk(v, edge.ImportSpec_Doc, -1, n.Doc)
+		}
+		if n.Name != nil {
+			walk(v, edge.ImportSpec_Name, -1, n.Name)
+		}
+		walk(v, edge.ImportSpec_Path, -1, n.Path)
+		if n.Comment != nil {
+			walk(v, edge.ImportSpec_Comment, -1, n.Comment)
+		}
+
+	case *ast.ValueSpec:
+		if n.Doc != nil {
+			walk(v, edge.ValueSpec_Doc, -1, n.Doc)
+		}
+		walkList(v, edge.ValueSpec_Names, n.Names)
+		if n.Type != nil {
+			walk(v, edge.ValueSpec_Type, -1, n.Type)
+		}
+		walkList(v, edge.ValueSpec_Values, n.Values)
+		if n.Comment != nil {
+			walk(v, edge.ValueSpec_Comment, -1, n.Comment)
+		}
+
+	case *ast.TypeSpec:
+		if n.Doc != nil {
+			walk(v, edge.TypeSpec_Doc, -1, n.Doc)
+		}
+		walk(v, edge.TypeSpec_Name, -1, n.Name)
+		if n.TypeParams != nil {
+			walk(v, edge.TypeSpec_TypeParams, -1, n.TypeParams)
+		}
+		walk(v, edge.TypeSpec_Type, -1, n.Type)
+		if n.Comment != nil {
+			walk(v, edge.TypeSpec_Comment, -1, n.Comment)
+		}
+
+	case *ast.BadDecl:
+		// nothing to do
+
+	case *ast.GenDecl:
+		if n.Doc != nil {
+			walk(v, edge.GenDecl_Doc, -1, n.Doc)
+		}
+		walkList(v, edge.GenDecl_Specs, n.Specs)
+
+	case *ast.FuncDecl:
+		if n.Doc != nil {
+			walk(v, edge.FuncDecl_Doc, -1, n.Doc)
+		}
+		if n.Recv != nil {
+			walk(v, edge.FuncDecl_Recv, -1, n.Recv)
+		}
+		walk(v, edge.FuncDecl_Name, -1, n.Name)
+		walk(v, edge.FuncDecl_Type, -1, n.Type)
+		if n.Body != nil {
+			walk(v, edge.FuncDecl_Body, -1, n.Body)
+		}
+
+	case *ast.File:
+		if n.Doc != nil {
+			walk(v, edge.File_Doc, -1, n.Doc)
+		}
+		walk(v, edge.File_Name, -1, n.Name)
+		walkList(v, edge.File_Decls, n.Decls)
+		// don't walk n.Comments - they have been
+		// visited already through the individual
+		// nodes
+
+	default:
+		// (includes *ast.Package)
+		panic(fmt.Sprintf("Walk: unexpected node type %T", n))
+	}
+
+	v.pop(node)
+}
@@ -364,12 +364,6 @@ type jsonPackage struct {
 	DepsErrors []*packagesinternal.PackageError
 }

-type jsonPackageError struct {
-	ImportStack []string
-	Pos         string
-	Err         string
-}
-
 func otherFiles(p *jsonPackage) [][]string {
 	return [][]string{p.CFiles, p.CXXFiles, p.MFiles, p.HFiles, p.FFiles, p.SFiles, p.SwigFiles, p.SwigCXXFiles, p.SysoFiles}
 }
@@ -28,11 +28,6 @@ type Event struct {
 	dynamic []label.Label  // dynamically sized storage for remaining labels
 }

-// eventLabelMap implements label.Map for a the labels of an Event.
-type eventLabelMap struct {
-	event Event
-}
-
 func (ev Event) At() time.Time { return ev.at }

 func (ev Event) Format(f fmt.State, r rune) {
@@ -569,7 +569,6 @@ func (p *iexporter) exportName(obj types.Object) (res string) {

 type iexporter struct {
 	fset    *token.FileSet
-	out     *bytes.Buffer
 	version int

 	shallow    bool                // don't put types from other packages in the index
@@ -0,0 +1,49 @@
+// Copyright 2025 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package typesinternal
+
+import (
+	"go/ast"
+	"go/token"
+	"go/types"
+)
+
+// NoEffects reports whether the expression has no side effects, i.e., it
+// does not modify the memory state. This function is conservative: it may
+// return false even when the expression has no effect.
+func NoEffects(info *types.Info, expr ast.Expr) bool {
+	noEffects := true
+	ast.Inspect(expr, func(n ast.Node) bool {
+		switch v := n.(type) {
+		case nil, *ast.Ident, *ast.BasicLit, *ast.BinaryExpr, *ast.ParenExpr,
+			*ast.SelectorExpr, *ast.IndexExpr, *ast.SliceExpr, *ast.TypeAssertExpr,
+			*ast.StarExpr, *ast.CompositeLit, *ast.ArrayType, *ast.StructType,
+			*ast.MapType, *ast.InterfaceType, *ast.KeyValueExpr:
+			// No effect
+		case *ast.UnaryExpr:
+			// Channel send <-ch has effects
+			if v.Op == token.ARROW {
+				noEffects = false
+			}
+		case *ast.CallExpr:
+			// Type conversion has no effects
+			if !info.Types[v.Fun].IsType() {
+				// TODO(adonovan): Add a case for built-in functions without side
+				// effects (by using callsPureBuiltin from tools/internal/refactor/inline)
+
+				noEffects = false
+			}
+		case *ast.FuncLit:
+			// A FuncLit has no effects, but do not descend into it.
+			return false
+		default:
+			// All other expressions have effects
+			noEffects = false
+		}
+
+		return noEffects
+	})
+	return noEffects
+}
@@ -0,0 +1,71 @@
+// Copyright 2025 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package typesinternal
+
+import (
+	"go/types"
+	"slices"
+)
+
+// IsTypeNamed reports whether t is (or is an alias for) a
+// package-level defined type with the given package path and one of
+// the given names. It returns false if t is nil.
+//
+// This function avoids allocating the concatenation of "pkg.Name",
+// which is important for the performance of syntax matching.
+func IsTypeNamed(t types.Type, pkgPath string, names ...string) bool {
+	if named, ok := types.Unalias(t).(*types.Named); ok {
+		tname := named.Obj()
+		return tname != nil &&
+			IsPackageLevel(tname) &&
+			tname.Pkg().Path() == pkgPath &&
+			slices.Contains(names, tname.Name())
+	}
+	return false
+}
+
+// IsPointerToNamed reports whether t is (or is an alias for) a pointer to a
+// package-level defined type with the given package path and one of the given
+// names. It returns false if t is not a pointer type.
+func IsPointerToNamed(t types.Type, pkgPath string, names ...string) bool {
+	r := Unpointer(t)
+	if r == t {
+		return false
+	}
+	return IsTypeNamed(r, pkgPath, names...)
+}
+
+// IsFunctionNamed reports whether obj is a package-level function
+// defined in the given package and has one of the given names.
+// It returns false if obj is nil.
+//
+// This function avoids allocating the concatenation of "pkg.Name",
+// which is important for the performance of syntax matching.
+func IsFunctionNamed(obj types.Object, pkgPath string, names ...string) bool {
+	f, ok := obj.(*types.Func)
+	return ok &&
+		IsPackageLevel(obj) &&
+		f.Pkg().Path() == pkgPath &&
+		f.Type().(*types.Signature).Recv() == nil &&
+		slices.Contains(names, f.Name())
+}
+
+// IsMethodNamed reports whether obj is a method defined on a
+// package-level type with the given package and type name, and has
+// one of the given names. It returns false if obj is nil.
+//
+// This function avoids allocating the concatenation of "pkg.TypeName.Name",
+// which is important for the performance of syntax matching.
+func IsMethodNamed(obj types.Object, pkgPath string, typeName string, names ...string) bool {
+	if fn, ok := obj.(*types.Func); ok {
+		if recv := fn.Type().(*types.Signature).Recv(); recv != nil {
+			_, T := ReceiverNamed(recv)
+			return T != nil &&
+				IsTypeNamed(T, pkgPath, typeName) &&
+				slices.Contains(names, fn.Name())
+		}
+	}
+	return false
+}
@@ -15,6 +15,14 @@ import (
 // file.
 // If the same package is imported multiple times, the last appearance is
 // recorded.
+//
+// TODO(adonovan): this function ignores the effect of shadowing. It
+// should accept a [token.Pos] and a [types.Info] and compute only the
+// set of imports that are not shadowed at that point, analogous to
+// [analysisinternal.AddImport]. It could also compute (as a side
+// effect) the set of additional imports required to ensure that there
+// is an accessible import for each necessary package, making it
+// converge even more closely with AddImport.
 func FileQualifier(f *ast.File, pkg *types.Package) types.Qualifier {
 	// Construct mapping of import paths to their defined names.
 	// It is only necessary to look at renaming imports.
@@ -2,8 +2,20 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.

-// Package typesinternal provides access to internal go/types APIs that are not
-// yet exported.
+// Package typesinternal provides helpful operators for dealing with
+// go/types:
+//
+//   - operators for querying typed syntax trees (e.g. [Imports], [IsFunctionNamed]);
+//   - functions for converting types to strings or syntax (e.g. [TypeExpr], FileQualifier]);
+//   - helpers for working with the [go/types] API (e.g. [NewTypesInfo]);
+//   - access to internal go/types APIs that are not yet
+//     exported (e.g. [SetUsesCgo], [ErrorCodeStartEnd], [VarKind]); and
+//   - common algorithms related to types (e.g. [TooNewStdSymbols]).
+//
+// See also:
+//   - [golang.org/x/tools/internal/astutil], for operations on untyped syntax;
+//   - [golang.org/x/tools/internal/analysisinernal], for helpers for analyzers;
+//   - [golang.org/x/tools/internal/refactor], for operators to compute text edits.
 package typesinternal

 import (
@@ -13,6 +25,7 @@ import (
 	"reflect"
 	"unsafe"

+	"golang.org/x/tools/go/ast/inspector"
 	"golang.org/x/tools/internal/aliases"
 )

@@ -60,6 +73,9 @@ func ErrorCodeStartEnd(err types.Error) (code ErrorCode, start, end token.Pos, o
 // which is often excessive.)
 //
 // If pkg is nil, it is equivalent to [*types.Package.Name].
+//
+// TODO(adonovan): all uses of this with TypeString should be
+// eliminated when https://go.dev/issues/75604 is resolved.
 func NameRelativeTo(pkg *types.Package) types.Qualifier {
 	return func(other *types.Package) string {
 		if pkg != nil && pkg == other {
@@ -153,3 +169,31 @@ func NewTypesInfo() *types.Info {
 		FileVersions: map[*ast.File]string{},
 	}
 }
+
+// EnclosingScope returns the innermost block logically enclosing the cursor.
+func EnclosingScope(info *types.Info, cur inspector.Cursor) *types.Scope {
+	for cur := range cur.Enclosing() {
+		n := cur.Node()
+		// A function's Scope is associated with its FuncType.
+		switch f := n.(type) {
+		case *ast.FuncDecl:
+			n = f.Type
+		case *ast.FuncLit:
+			n = f.Type
+		}
+		if b := info.Scopes[n]; b != nil {
+			return b
+		}
+	}
+	panic("no Scope for *ast.File")
+}
+
+// Imports reports whether path is imported by pkg.
+func Imports(pkg *types.Package, path string) bool {
+	for _, imp := range pkg.Imports() {
+		if imp.Path() == path {
+			return true
+		}
+	}
+	return false
+}
@@ -204,23 +204,12 @@ func ZeroExpr(t types.Type, qual types.Qualifier) (_ ast.Expr, isValid bool) {
 	}
 }

-// IsZeroExpr uses simple syntactic heuristics to report whether expr
-// is a obvious zero value, such as 0, "", nil, or false.
-// It cannot do better without type information.
-func IsZeroExpr(expr ast.Expr) bool {
-	switch e := expr.(type) {
-	case *ast.BasicLit:
-		return e.Value == "0" || e.Value == `""`
-	case *ast.Ident:
-		return e.Name == "nil" || e.Name == "false"
-	default:
-		return false
-	}
-}
-
 // TypeExpr returns syntax for the specified type. References to named types
 // are qualified by an appropriate (optional) qualifier function.
 // It may panic for types such as Tuple or Union.
+//
+// See also https://go.dev/issues/75604, which will provide a robust
+// Type-to-valid-Go-syntax formatter.
 func TypeExpr(t types.Type, qual types.Qualifier) ast.Expr {
 	switch t := t.(type) {
 	case *types.Basic:
@@ -820,7 +820,7 @@ go.yaml.in/yaml/v2
 # go.yaml.in/yaml/v3 v3.0.4
 ## explicit; go 1.16
 go.yaml.in/yaml/v3
-# golang.org/x/crypto v0.42.0
+# golang.org/x/crypto v0.43.0
 ## explicit; go 1.24.0
 golang.org/x/crypto/bcrypt
 golang.org/x/crypto/blowfish
@@ -837,7 +837,7 @@ golang.org/x/crypto/ssh/internal/bcrypt_pbkdf
 golang.org/x/mod/internal/lazyregexp
 golang.org/x/mod/module
 golang.org/x/mod/semver
-# golang.org/x/net v0.44.0
+# golang.org/x/net v0.46.0
 ## explicit; go 1.24.0
 golang.org/x/net/html
 golang.org/x/net/html/atom
@@ -869,7 +869,7 @@ golang.org/x/sys/windows/registry
 # golang.org/x/term v0.37.0
 ## explicit; go 1.24.0
 golang.org/x/term
-# golang.org/x/text v0.29.0
+# golang.org/x/text v0.31.0
 ## explicit; go 1.24.0
 golang.org/x/text/cases
 golang.org/x/text/feature/plural
@@ -892,9 +892,11 @@ golang.org/x/text/width
 # golang.org/x/time v0.14.0
 ## explicit; go 1.24.0
 golang.org/x/time/rate
-# golang.org/x/tools v0.37.0
+# golang.org/x/tools v0.38.0
 ## explicit; go 1.24.0
 golang.org/x/tools/cmd/stringer
+golang.org/x/tools/go/ast/edge
+golang.org/x/tools/go/ast/inspector
 golang.org/x/tools/go/gcexportdata
 golang.org/x/tools/go/packages
 golang.org/x/tools/go/types/objectpath