dap: properly map source paths to client side paths

Properly map the source paths from the metadata in the solve to the
client side paths. The source path returns is relative to the context
that gets uploaded which is usually a subdirectory. The original code
noticed this when mapping the paths but made the invalid assumption that
the dockerfile would always be in the context path so it combined the
dockerfile name with the context path.

It is possible for the dockerfile to be in a subdirectory of the
context. In which case, we computed the paths incorrectly.

This modifies DAP to instead use the `DockerfileMappingDst` and
`DockerfileMappingSrc` which are special included variables to the
inputs that get filled in during the build for the purpose of mapping
the source path to the client side path.

Tests have also been added for this functionality to ensure it doesn't
break again. This should work with both absolute and relative paths
although absolute paths should probably be preferred for usage just
because they're less likely to result in weird things happening.

The sources are also normalized to always convert the source filenames
to absolute paths and DAP itself will accept relative paths but will
only ever communicate in absolute paths. When you set a breakpoint, it
will convert it to an absolute path and reference it in that way rather
than a relative path.

Signed-off-by: Jonathan A. Sternberg <jonathan.sternberg@docker.com>

dap/adapter.go

@@ -7,7 +7,6 @@ import (
 	"fmt"
 	"io"
 	"path"
-	"path/filepath"
 	"slices"
 	"sync"
 	"sync/atomic"
@@ -598,14 +597,14 @@ func (b *breakpointMap) Set(fname string, sbps []dap.SourceBreakpoint) (breakpoi
 	return breakpoints
 }
 
-func (b *breakpointMap) Intersect(ctx Context, src *pb.Source, ws string) map[digest.Digest]int {
+func (b *breakpointMap) Intersect(ctx Context, src *pb.Source) map[digest.Digest]int {
 	b.mu.Lock()
 	defer b.mu.Unlock()
 
 	digests := make(map[digest.Digest]int)
 
 	for dgst, locs := range src.Locations {
-		if id := b.intersect(ctx, src, locs, ws); id > 0 {
+		if id := b.intersect(ctx, src, locs); id > 0 {
 			digests[digest.Digest(dgst)] = id
 		}
 	}
@@ -613,7 +612,7 @@ func (b *breakpointMap) Intersect(ctx Context, src *pb.Source, ws string) map[di
 	// Mark unverified breakpoints as failed at this point since we couldn't find an area
 	// in the source where they applied.
 	for _, info := range src.Infos {
-		fname := filepath.Join(ws, info.Filename)
+		fname := info.Filename
 
 		bps := b.byPath[fname]
 		for _, bp := range bps {
@@ -633,7 +632,7 @@ func (b *breakpointMap) Intersect(ctx Context, src *pb.Source, ws string) map[di
 	return digests
 }
 
-func (b *breakpointMap) intersect(ctx Context, src *pb.Source, locs *pb.Locations, ws string) int {
+func (b *breakpointMap) intersect(ctx Context, src *pb.Source, locs *pb.Locations) int {
 	overlaps := func(r *pb.Range, bp *dap.Breakpoint) bool {
 		if bp.Line < int(r.Start.Line) || bp.Line > int(r.End.Line) {
 			return false
@@ -654,7 +653,7 @@ func (b *breakpointMap) intersect(ctx Context, src *pb.Source, locs *pb.Location
 		r := loc.Ranges[0]
 
 		info := src.Infos[loc.SourceIndex]
-		fname := filepath.Join(ws, info.Filename)
+		fname := info.Filename
 
 		bps := b.byPath[fname]
 		if len(bps) == 0 {

dap/adapter_test.go

@@ -187,12 +187,12 @@ func TestBreakpointMapIntersectVerified(t *testing.T) {
 	src := &pb.Source{
 		Locations: srcLocs,
 		Infos: []*pb.SourceInfo{
-			{Filename: filename},
+			{Filename: fpath},
 		},
 	}
 
 	ctx := newBreakpointTestContext(t)
-	digests := bm.Intersect(ctx, src, ws)
+	digests := bm.Intersect(ctx, src)
 	wantMatches := 0
 	for _, bc := range breakpointCases {
 		if bc.expectVerified {

dap/thread.go

@@ -2,9 +2,9 @@ package dap
 
 import (
 	"context"
-	"path"
 	"path/filepath"
 	"slices"
+	"strings"
 	"sync"
 
 	"github.com/docker/buildx/build"
@@ -31,10 +31,10 @@ type thread struct {
 	variables *variableReferences
 
 	// Inputs to the evaluate call.
-	c          gateway.Client
+	c             gateway.Client
-	ref        gateway.Reference
+	ref           gateway.Reference
-	meta       map[string][]byte
+	meta          map[string][]byte
-	sourcePath string
+	sourceInfoMap func(*pb.Source) *pb.Source
 
 	// LLB state for the evaluate call.
 	def    *llb.Definition
@@ -107,14 +107,21 @@ func (t *thread) init(ctx Context, c gateway.Client, ref gateway.Reference, meta
 	t.c = c
 	t.ref = ref
 	t.meta = meta
+	t.sourceInfoMap = func(s *pb.Source) *pb.Source {
+		s = s.CloneVT()
+		for _, sinfo := range s.Infos {
+			// Map the filename from the source info from the frontend location to the
+			// client location.
+			fname := strings.Replace(sinfo.Filename, inputs.DockerfileMappingDst, inputs.DockerfileMappingSrc, 1)
 
-	// Combine the dockerfile directory with the context path to find the
+			// Convert to an absolute path.
-	// real base path. The frontend will report the base path as the filename.
+			if abspath, err := filepath.Abs(fname); err == nil {
-	dir := path.Dir(inputs.DockerfilePath)
+				fname = abspath
-	if !path.IsAbs(dir) {
+			}
-		dir = path.Join(inputs.ContextPath, dir)
+			sinfo.Filename = fname
+		}
+		return s
 	}
-	t.sourcePath = dir
 
 	if err := t.getLLBState(ctx); err != nil {
 		return err
@@ -252,7 +259,7 @@ func (t *thread) getStackFrame(dgst digest.Digest, next *step) *frame {
 		f.setNameFromMeta(meta)
 	}
 	if loc, ok := t.def.Source.Locations[string(dgst)]; ok {
-		f.fillLocation(t.def, loc, t.sourcePath, next)
+		f.fillLocation(t.def, loc, next)
 	}
 	t.frames[int32(f.Id)] = f
 	return f
@@ -296,7 +303,6 @@ func (t *thread) reset() {
 	t.c = nil
 	t.ref = nil
 	t.meta = nil
-	t.sourcePath = ""
 	t.ops = nil
 }
 
@@ -462,9 +468,12 @@ func (t *thread) getLLBState(ctx Context) error {
 		return err
 	}
 
+	if t.sourceInfoMap != nil {
+		t.def.Source = t.sourceInfoMap(t.def.Source)
+	}
+
 	for _, src := range t.def.Source.Infos {
-		fname := filepath.Join(t.sourcePath, src.Filename)
+		t.sourceMap.Put(ctx, src.Filename, src.Data)
-		t.sourceMap.Put(ctx, fname, src.Data)
 	}
 
 	t.ops = make(map[digest.Digest]*pb.Op, len(t.def.Def))
@@ -483,7 +492,7 @@ func (t *thread) getLLBState(ctx Context) error {
 }
 
 func (t *thread) setBreakpoints(ctx Context) {
-	t.bps = t.breakpointMap.Intersect(ctx, t.def.Source, t.sourcePath)
+	t.bps = t.breakpointMap.Intersect(ctx, t.def.Source)
 }
 
 func (t *thread) seekNext(ctx Context, from *step, action stepType) (string, *step, map[string]gateway.Reference, error) {

dap/variables.go

@@ -38,7 +38,7 @@ func (f *frame) setNameFromMeta(meta llb.OpMetadata) {
 	// TODO: should we infer the name from somewhere else?
 }
 
-func (f *frame) fillLocation(def *llb.Definition, loc *pb.Locations, ws string, next *step) {
+func (f *frame) fillLocation(def *llb.Definition, loc *pb.Locations, next *step) {
 	for _, l := range loc.Locations {
 		for _, r := range l.Ranges {
 			if next != nil && f.Line != 0 {
@@ -57,7 +57,7 @@ func (f *frame) fillLocation(def *llb.Definition, loc *pb.Locations, ws string,
 			info := def.Source.Infos[l.SourceIndex]
 			f.Source = &dap.Source{
 				Name: path.Base(info.Filename),
-				Path: filepath.Join(ws, info.Filename),
+				Path: info.Filename,
 			}
 
 			// If we do not have a next operation, then we don't have

tests/build.go

@@ -107,7 +107,7 @@ COPY --from=base /etc/bar /bar
 `)
 	dir := tmpdir(
 		t,
-		fstest.CreateFile("foo", []byte("foo"), 0600),
+		fstest.CreateFile("foo", []byte("foo"), 0o600),
 	)
 
 	cmd := buildxCmd(sb, withDir(dir), withArgs("build", "--progress=quiet", "-f-", dir))
@@ -124,8 +124,8 @@ COPY foo /foo
 `)
 		dir := tmpdir(
 			t,
-			fstest.CreateFile("Dockerfile", dockerfile, 0600),
+			fstest.CreateFile("Dockerfile", dockerfile, 0o600),
-			fstest.CreateFile("foo", []byte("foo"), 0600),
+			fstest.CreateFile("foo", []byte("foo"), 0o600),
 		)
 		dirDest := t.TempDir()
 
@@ -149,8 +149,8 @@ COPY foo /foo
 `)
 		dir := tmpdir(
 			t,
-			fstest.CreateFile("Dockerfile", dockerfile, 0600),
+			fstest.CreateFile("Dockerfile", dockerfile, 0o600),
-			fstest.CreateFile("foo", []byte("foo"), 0600),
+			fstest.CreateFile("foo", []byte("foo"), 0o600),
 		)
 		dirDest := t.TempDir()
 
@@ -176,8 +176,8 @@ COPY foo /foo
 `)
 		dir := tmpdir(
 			t,
-			fstest.CreateFile("Dockerfile", dockerfile, 0600),
+			fstest.CreateFile("Dockerfile", dockerfile, 0o600),
-			fstest.CreateFile("foo", []byte("foo"), 0600),
+			fstest.CreateFile("foo", []byte("foo"), 0o600),
 		)
 		dirDest := t.TempDir()
 
@@ -209,8 +209,8 @@ COPY foo /foo
 `)
 		dir := tmpdir(
 			t,
-			fstest.CreateFile("Dockerfile", dockerfile, 0600),
+			fstest.CreateFile("Dockerfile", dockerfile, 0o600),
-			fstest.CreateFile("foo", []byte("foo"), 0600),
+			fstest.CreateFile("foo", []byte("foo"), 0o600),
 		)
 		dirDest := t.TempDir()
 
@@ -242,8 +242,8 @@ COPY foo /foo
 `)
 		dir := tmpdir(
 			t,
-			fstest.CreateFile("Dockerfile", dockerfile, 0600),
+			fstest.CreateFile("Dockerfile", dockerfile, 0o600),
-			fstest.CreateFile("foo", []byte("foo"), 0600),
+			fstest.CreateFile("foo", []byte("foo"), 0o600),
 		)
 		dirDest := t.TempDir()
 
@@ -275,8 +275,8 @@ COPY foo /foo
 `)
 	dir := tmpdir(
 		t,
-		fstest.CreateFile("Dockerfile", dockerfile, 0600),
+		fstest.CreateFile("Dockerfile", dockerfile, 0o600),
-		fstest.CreateFile("foo", []byte("foo"), 0600),
+		fstest.CreateFile("foo", []byte("foo"), 0o600),
 	)
 	dirDest := t.TempDir()
 
@@ -314,8 +314,8 @@ COPY --from=base /etc/bar /bar
 `)
 	dir := tmpdir(
 		t,
-		fstest.CreateFile("build.Dockerfile", dockerfile, 0600),
+		fstest.CreateFile("build.Dockerfile", dockerfile, 0o600),
-		fstest.CreateFile("foo", []byte("foo"), 0600),
+		fstest.CreateFile("foo", []byte("foo"), 0o600),
 	)
 
 	out, err := buildCmd(sb, withDir(dir), withArgs(
@@ -359,7 +359,7 @@ COPY --from=base /etc/bar /bar
 `)
 	dir := tmpdir(
 		t,
-		fstest.CreateFile("foo", []byte("foo"), 0600),
+		fstest.CreateFile("foo", []byte("foo"), 0o600),
 	)
 
 	cmd := buildxCmd(sb, withDir(dir), withArgs("build", "--progress=quiet", "--metadata-file", filepath.Join(dir, "md.json"), "-f-", dir))
@@ -397,8 +397,8 @@ COPY foo /foo
 `)
 	dir := tmpdir(
 		t,
-		fstest.CreateFile("build.Dockerfile", dockerfile, 0600),
+		fstest.CreateFile("build.Dockerfile", dockerfile, 0o600),
-		fstest.CreateFile("foo", []byte("foo"), 0600),
+		fstest.CreateFile("foo", []byte("foo"), 0o600),
 	)
 	dirDest := t.TempDir()
 
@@ -534,7 +534,7 @@ func testImageIDOutput(t *testing.T, sb integration.Sandbox) {
 	dockerfile := []byte(`FROM busybox:latest`)
 
 	dir := tmpdir(t,
-		fstest.CreateFile("Dockerfile", dockerfile, 0600),
+		fstest.CreateFile("Dockerfile", dockerfile, 0o600),
 	)
 	targetDir := t.TempDir()
 
@@ -607,7 +607,7 @@ func testBuildMobyFromLocalImage(t *testing.T, sb integration.Sandbox) {
 
 	// build image
 	dockerfile := []byte(`FROM buildx-test:busybox`)
-	dir := tmpdir(t, fstest.CreateFile("Dockerfile", dockerfile, 0600))
+	dir := tmpdir(t, fstest.CreateFile("Dockerfile", dockerfile, 0o600))
 	cmd = buildxCmd(
 		sb,
 		withArgs("build", "-q", "--output=type=cacheonly", dir),
@@ -626,7 +626,7 @@ func testBuildMobyFromLocalImage(t *testing.T, sb integration.Sandbox) {
 FROM busybox:1.35
 RUN busybox | head -1 | grep v1.36.1
 `)
-	dir = tmpdir(t, fstest.CreateFile("Dockerfile", dockerfile, 0600))
+	dir = tmpdir(t, fstest.CreateFile("Dockerfile", dockerfile, 0o600))
 	cmd = buildxCmd(
 		sb,
 		withArgs("build", "-q", "--output=type=cacheonly", dir),
@@ -642,7 +642,7 @@ func testBuildDetailsLink(t *testing.T, sb integration.Sandbox) {
 	// build simple dockerfile
 	dockerfile := []byte(`FROM busybox:latest
 RUN echo foo > /bar`)
-	dir := tmpdir(t, fstest.CreateFile("Dockerfile", dockerfile, 0600))
+	dir := tmpdir(t, fstest.CreateFile("Dockerfile", dockerfile, 0o600))
 	cmd := buildxCmd(sb, withArgs("build", "--output=type=cacheonly", dir))
 	out, err := cmd.CombinedOutput()
 	require.NoError(t, err, string(out))
@@ -652,7 +652,7 @@ RUN echo foo > /bar`)
 	home, err := os.UserHomeDir() // TODO: sandbox should create a temp home dir and expose it through its interface
 	require.NoError(t, err)
 	dbDir := path.Join(home, ".docker", "desktop-build")
-	require.NoError(t, os.MkdirAll(dbDir, 0755))
+	require.NoError(t, os.MkdirAll(dbDir, 0o755))
 	dblaFile, err := os.Create(path.Join(dbDir, ".lastaccess"))
 	require.NoError(t, err)
 	defer func() {
@@ -671,7 +671,7 @@ RUN echo foo > /bar`)
 	// build erroneous dockerfile
 	dockerfile = []byte(`FROM busybox:latest
 RUN exit 1`)
-	dir = tmpdir(t, fstest.CreateFile("Dockerfile", dockerfile, 0600))
+	dir = tmpdir(t, fstest.CreateFile("Dockerfile", dockerfile, 0o600))
 	cmd = buildxCmd(sb, withArgs("build", "--output=type=cacheonly", dir))
 	out, err = cmd.CombinedOutput()
 	require.Error(t, err, string(out))
@@ -802,8 +802,8 @@ func testBuildMultiPlatform(t *testing.T, sb integration.Sandbox) {
 	`)
 	dir := tmpdir(
 		t,
-		fstest.CreateFile("Dockerfile", dockerfile, 0600),
+		fstest.CreateFile("Dockerfile", dockerfile, 0o600),
-		fstest.CreateFile("foo", []byte("foo"), 0600),
+		fstest.CreateFile("foo", []byte("foo"), 0o600),
 	)
 	registry, err := sb.NewRegistry()
 	if errors.Is(err, integration.ErrRequirements) {
@@ -838,7 +838,7 @@ func testDockerHostGateway(t *testing.T, sb integration.Sandbox) {
 FROM busybox
 RUN ping -c 1 buildx.host-gateway-ip.local
 `)
-	dir := tmpdir(t, fstest.CreateFile("Dockerfile", dockerfile, 0600))
+	dir := tmpdir(t, fstest.CreateFile("Dockerfile", dockerfile, 0o600))
 	cmd := buildxCmd(sb, withArgs("build", "--add-host=buildx.host-gateway-ip.local:host-gateway", "--output=type=cacheonly", dir))
 	out, err := cmd.CombinedOutput()
 	if !isDockerWorker(sb) {
@@ -877,7 +877,7 @@ RUN ip a show eth0 | awk '/inet / {split($2, a, "/"); print a[1]}' > /ip-bridge.
 RUN --network=host ip a show eth0 | awk '/inet / {split($2, a, "/"); print a[1]}' > /ip-host.txt
 FROM scratch
 COPY --from=build /ip*.txt /`)
-	dir := tmpdir(t, fstest.CreateFile("Dockerfile", dockerfile, 0600))
+	dir := tmpdir(t, fstest.CreateFile("Dockerfile", dockerfile, 0o600))
 
 	cmd := buildxCmd(sb, withArgs("build", "--allow=network.host", fmt.Sprintf("--output=type=local,dest=%s", dir), dir))
 	cmd.Env = append(cmd.Env, "BUILDX_BUILDER="+builderName)
@@ -912,7 +912,7 @@ COPY --from=build /shmsize /
 	`)
 	dir := tmpdir(
 		t,
-		fstest.CreateFile("Dockerfile", dockerfile, 0600),
+		fstest.CreateFile("Dockerfile", dockerfile, 0o600),
 	)
 
 	cmd := buildxCmd(sb, withArgs("build", "--shm-size=128m", fmt.Sprintf("--output=type=local,dest=%s", dir), dir))
@@ -933,7 +933,7 @@ COPY --from=build /ulimit /
 	`)
 	dir := tmpdir(
 		t,
-		fstest.CreateFile("Dockerfile", dockerfile, 0600),
+		fstest.CreateFile("Dockerfile", dockerfile, 0o600),
 	)
 
 	cmd := buildxCmd(sb, withArgs("build", "--ulimit=nofile=1024:1024", fmt.Sprintf("--output=type=local,dest=%s", dir), dir))
@@ -1034,8 +1034,8 @@ func buildMetadataProvenanceMultiplatform(t *testing.T, sb integration.Sandbox,
 	`)
 	dir := tmpdir(
 		t,
-		fstest.CreateFile("Dockerfile", dockerfile, 0600),
+		fstest.CreateFile("Dockerfile", dockerfile, 0o600),
-		fstest.CreateFile("foo", []byte("foo"), 0600),
+		fstest.CreateFile("foo", []byte("foo"), 0o600),
 	)
 
 	registry, err := sb.NewRegistry()
@@ -1122,7 +1122,7 @@ COPy --from=base \
 	`)
 	dir := tmpdir(
 		t,
-		fstest.CreateFile("Dockerfile", dockerfile, 0600),
+		fstest.CreateFile("Dockerfile", dockerfile, 0o600),
 	)
 
 	cmd := buildxCmd(
@@ -1258,8 +1258,8 @@ COPY --from=build /token /
 	`)
 	dir := tmpdir(
 		t,
-		fstest.CreateFile("Dockerfile", dockerfile, 0600),
+		fstest.CreateFile("Dockerfile", dockerfile, 0o600),
-		fstest.CreateFile("tokenfile", []byte(token), 0600),
+		fstest.CreateFile("tokenfile", []byte(token), 0o600),
 	)
 
 	t.Run("env", func(t *testing.T) {
@@ -1347,7 +1347,7 @@ COPy --from=base \
 	`)
 		dir := tmpdir(
 			t,
-			fstest.CreateFile("Dockerfile", dockerfile, 0600),
+			fstest.CreateFile("Dockerfile", dockerfile, 0o600),
 		)
 
 		cmd := buildxCmd(sb, withArgs("build", "--call=check,format=json", dir))
@@ -1382,7 +1382,7 @@ FROM second
 	`)
 		dir := tmpdir(
 			t,
-			fstest.CreateFile("Dockerfile", dockerfile, 0600),
+			fstest.CreateFile("Dockerfile", dockerfile, 0o600),
 		)
 
 		cmd := buildxCmd(sb, withArgs("build", "--build-arg=BAR=678", "--target=target", "--call=outline,format=json", dir))
@@ -1423,7 +1423,7 @@ ARG FOO=bar
 `)
 		dir := tmpdir(
 			t,
-			fstest.CreateFile("Dockerfile", dockerfile, 0600),
+			fstest.CreateFile("Dockerfile", dockerfile, 0o600),
 		)
 
 		runOutline := func(args ...string) string {
@@ -1459,7 +1459,7 @@ FROM second AS binary
 	`)
 		dir := tmpdir(
 			t,
-			fstest.CreateFile("Dockerfile", dockerfile, 0600),
+			fstest.CreateFile("Dockerfile", dockerfile, 0o600),
 		)
 
 		cmd := buildxCmd(sb, withArgs("build", "--call=targets,format=json", dir))
@@ -1501,7 +1501,7 @@ COPy --from=base \
 	`)
 		dir := tmpdir(
 			t,
-			fstest.CreateFile("Dockerfile", dockerfile, 0600),
+			fstest.CreateFile("Dockerfile", dockerfile, 0o600),
 		)
 
 		cmd := buildxCmd(sb, withArgs("build", "--call=check,format=json", "--metadata-file", filepath.Join(dir, "md.json"), dir))
@@ -1537,7 +1537,7 @@ COPY Dockerfile .
 	`)
 		dir := tmpdir(
 			t,
-			fstest.CreateFile("Dockerfile", dockerfile, 0600),
+			fstest.CreateFile("Dockerfile", dockerfile, 0o600),
 		)
 
 		cmd := buildxCmd(sb, withArgs("build", "--call=check", dir))
@@ -1556,7 +1556,7 @@ COPY Dockerfile .
 	`)
 		dir := tmpdir(
 			t,
-			fstest.CreateFile("Dockerfile", dockerfile, 0600),
+			fstest.CreateFile("Dockerfile", dockerfile, 0o600),
 		)
 
 		cmd := buildxCmd(sb, withArgs("build", "--call=check", dir))
@@ -1575,7 +1575,7 @@ cOpy Dockerfile .
 	`)
 		dir := tmpdir(
 			t,
-			fstest.CreateFile("Dockerfile", dockerfile, 0600),
+			fstest.CreateFile("Dockerfile", dockerfile, 0o600),
 		)
 
 		cmd := buildxCmd(sb, withArgs("build", "--call=check", dir))
@@ -1594,8 +1594,8 @@ cOpy Dockerfile .
 	`)
 		dir := tmpdir(
 			t,
-			fstest.CreateDir("subdir", 0700),
+			fstest.CreateDir("subdir", 0o700),
-			fstest.CreateFile("subdir/Dockerfile", dockerfile, 0600),
+			fstest.CreateFile("subdir/Dockerfile", dockerfile, 0o600),
 		)
 		dockerfilePath := filepath.Join(dir, "subdir", "Dockerfile")
 
@@ -1618,7 +1618,7 @@ RUN cat /etc/hosts | grep myhost | grep 1.2.3.4
 RUN cat /etc/hosts | grep myhostmulti | grep 162.242.195.81
 RUN cat /etc/hosts | grep myhostmulti | grep 162.242.195.82
 `)
-	dir := tmpdir(t, fstest.CreateFile("Dockerfile", dockerfile, 0600))
+	dir := tmpdir(t, fstest.CreateFile("Dockerfile", dockerfile, 0o600))
 	cmd := buildxCmd(sb, withArgs("build",
 		"--add-host=myhost=1.2.3.4",
 		"--add-host=myhostmulti=162.242.195.81",
@@ -1649,10 +1649,9 @@ RUN cp /etc/foo /etc/bar
 FROM scratch
 COPY --from=base /etc/bar /bar
 `)
-	dir := tmpdir(
+	dir := tmpdir(t,
-		t,
+		fstest.CreateFile("Dockerfile", dockerfile, 0o600),
-		fstest.CreateFile("Dockerfile", dockerfile, 0600),
+		fstest.CreateFile("foo", []byte("foo"), 0o600),
-		fstest.CreateFile("foo", []byte("foo"), 0600),
 	)
 	return dir
 }

tests/dap_build.go

@@ -11,6 +11,7 @@ import (
 	"testing"
 	"time"
 
+	"github.com/containerd/continuity/fs/fstest"
 	"github.com/docker/buildx/commands"
 	debug "github.com/docker/buildx/dap"
 	"github.com/docker/buildx/dap/common"
@@ -78,6 +79,7 @@ var dapBuildTests = []func(t *testing.T, sb integration.Sandbox){
 	testDapBuildStopOnEntry,
 	testDapBuildSetBreakpoints,
 	testDapBuildVerifiedBreakpoints,
+	testDapBuildLoadedSource,
 	testDapBuildStepIn,
 	testDapBuildStepNext,
 	testDapBuildStepOut,
@@ -250,6 +252,103 @@ func testDapBuildVerifiedBreakpoints(t *testing.T, sb integration.Sandbox) {
 	require.ErrorAs(t, done(true), &exitErr)
 }
 
+func testDapBuildLoadedSource(t *testing.T, sb integration.Sandbox) {
+	type test struct {
+		Name           string
+		ContextPath    string
+		DockerfilePath string
+	}
+
+	runTest := func(t *testing.T, tt test, abspath bool) string {
+		dockerfile := []byte(`
+FROM busybox:latest AS base
+COPY foo /etc/foo
+RUN cp /etc/foo /etc/bar
+
+FROM scratch
+COPY --from=base /etc/bar /bar
+`)
+
+		appliers := []fstest.Applier{}
+		if tt.ContextPath != "" {
+			appliers = append(appliers, fstest.CreateDir(tt.ContextPath, 0o700))
+		}
+		if tt.DockerfilePath != "" {
+			appliers = append(appliers, fstest.CreateDir(path.Join(tt.ContextPath, tt.DockerfilePath), 0o700))
+		}
+		appliers = append(appliers,
+			fstest.CreateFile(path.Join(tt.ContextPath, tt.DockerfilePath, "Dockerfile"), dockerfile, 0o600),
+			fstest.CreateFile(path.Join(tt.ContextPath, "foo"), []byte("foo"), 0o600),
+		)
+		dir := tmpdir(t, appliers...)
+
+		client, done, err := dapBuildCmd(t, sb, withDir(dir))
+		require.NoError(t, err)
+
+		var source *dap.Source
+		client.RegisterEvent("loadedSource", func(em dap.EventMessage) {
+			e := em.(*dap.LoadedSourceEvent)
+			source = &e.Body.Source
+		})
+
+		launchCfg := commands.LaunchConfig{
+			Config: common.Config{
+				StopOnEntry: true,
+			},
+		}
+		if abspath {
+			launchCfg.ContextPath = path.Join(dir, tt.ContextPath)
+		} else {
+			launchCfg.ContextPath = tt.ContextPath
+		}
+		launchCfg.Dockerfile = path.Join(launchCfg.ContextPath, tt.DockerfilePath, "Dockerfile")
+		doLaunch(t, client, launchCfg)
+
+		interruptCh := pollInterruptEvents(client)
+		stopped := waitForInterrupt[*dap.StoppedEvent](t, interruptCh)
+		require.NotNil(t, stopped)
+
+		expected := path.Join(dir, tt.ContextPath, tt.DockerfilePath, "Dockerfile")
+		require.NotNil(t, source)
+		require.Equal(t, expected, source.Path)
+		require.Equal(t, "Dockerfile", source.Name)
+
+		var exitErr *exec.ExitError
+		require.ErrorAs(t, done(true), &exitErr)
+		return dir
+	}
+
+	for _, tt := range []test{
+		{
+			Name:        "base path",
+			ContextPath: ".",
+		},
+		{
+			Name:        "nested context",
+			ContextPath: "nested",
+		},
+		{
+			Name:           "nested dockerfile",
+			ContextPath:    ".",
+			DockerfilePath: "nested",
+		},
+		{
+			Name:           "both nested",
+			ContextPath:    "nested",
+			DockerfilePath: "subdir",
+		},
+	} {
+		t.Run(tt.Name, func(t *testing.T) {
+			t.Run("absolute paths", func(t *testing.T) {
+				runTest(t, tt, true)
+			})
+			t.Run("relative paths", func(t *testing.T) {
+				runTest(t, tt, false)
+			})
+		})
+	}
+}
+
 func testDapBuildStepIn(t *testing.T, sb integration.Sandbox) {
 	dir := createTestProject(t)
 	client, done, err := dapBuildCmd(t, sb, withArgs(dir))