build: split out node resolver

Signed-off-by: Justin Chadwell <me@jedevc.com>
2025-12-04 09:48:36 +00:00
parent 4eb80cafb9
commit 3e413a05df
4 changed files with 82 additions and 61 deletions
@@ -0,0 +1,370 @@
+package resolver
+
+import (
+	"context"
+	"fmt"
+	"slices"
+	"strconv"
+	"sync"
+
+	"github.com/containerd/platforms"
+	"github.com/docker/buildx/builder"
+	"github.com/docker/buildx/driver"
+	"github.com/docker/buildx/util/progress"
+	"github.com/moby/buildkit/client"
+	gateway "github.com/moby/buildkit/frontend/gateway/client"
+	"github.com/moby/buildkit/util/flightcontrol"
+	"github.com/moby/buildkit/util/tracing"
+	ocispecs "github.com/opencontainers/image-spec/specs-go/v1"
+	"github.com/pkg/errors"
+	"go.opentelemetry.io/otel/trace"
+	"golang.org/x/sync/errgroup"
+)
+
+func Resolve(ctx context.Context, nodes []builder.Node, platforms []ocispecs.Platform, pw progress.Writer) ([]*ResolvedNode, error) {
+	result, err := ResolveAll(ctx, nodes, map[string][]ocispecs.Platform{"default": platforms}, pw)
+	if err != nil {
+		return nil, err
+	}
+	return result["default"], nil
+}
+
+func ResolveAll(ctx context.Context, nodes []builder.Node, optPlatforms map[string][]ocispecs.Platform, pw progress.Writer) (map[string][]*ResolvedNode, error) {
+	driverRes := newDriverResolver(nodes)
+	drivers, err := driverRes.Resolve(ctx, optPlatforms, pw)
+	if err != nil {
+		return nil, err
+	}
+	return drivers, err
+}
+
+type ResolvedNode struct {
+	resolver    *nodeResolver
+	driverIndex int
+	platforms   []ocispecs.Platform
+}
+
+func (dp ResolvedNode) Key() string {
+	return strconv.Itoa(dp.driverIndex)
+}
+
+func (dp ResolvedNode) Node() builder.Node {
+	return dp.resolver.nodes[dp.driverIndex]
+}
+
+func (dp ResolvedNode) Platforms() []ocispecs.Platform {
+	return dp.platforms
+}
+
+func (dp ResolvedNode) Client(ctx context.Context) (*client.Client, error) {
+	clients, err := dp.resolver.boot(ctx, []int{dp.driverIndex}, nil)
+	if err != nil {
+		return nil, err
+	}
+	return clients[0], nil
+}
+
+func (dp ResolvedNode) BuildOpts(ctx context.Context) (gateway.BuildOpts, error) {
+	opts, err := dp.resolver.opts(ctx, []int{dp.driverIndex}, nil)
+	if err != nil {
+		return gateway.BuildOpts{}, err
+	}
+	return opts[0], nil
+}
+
+type matchMaker func(ocispecs.Platform) platforms.MatchComparer
+
+type cachedGroup[T any] struct {
+	g       flightcontrol.Group[T]
+	cache   map[int]T
+	cacheMu sync.Mutex
+}
+
+func newCachedGroup[T any]() cachedGroup[T] {
+	return cachedGroup[T]{
+		cache: map[int]T{},
+	}
+}
+
+type nodeResolver struct {
+	nodes     []builder.Node
+	clients   cachedGroup[*client.Client]
+	buildOpts cachedGroup[gateway.BuildOpts]
+}
+
+func newDriverResolver(nodes []builder.Node) *nodeResolver {
+	r := &nodeResolver{
+		nodes:     nodes,
+		clients:   newCachedGroup[*client.Client](),
+		buildOpts: newCachedGroup[gateway.BuildOpts](),
+	}
+	return r
+}
+
+func (r *nodeResolver) Resolve(ctx context.Context, optPlatforms map[string][]ocispecs.Platform, pw progress.Writer) (map[string][]*ResolvedNode, error) {
+	if len(r.nodes) == 0 {
+		return nil, nil
+	}
+
+	nodes := map[string][]*ResolvedNode{}
+	for k, optPlatforms := range optPlatforms {
+		node, perfect, err := r.resolve(ctx, optPlatforms, pw, platforms.OnlyStrict, nil)
+		if err != nil {
+			return nil, err
+		}
+		if !perfect {
+			break
+		}
+		nodes[k] = node
+	}
+	if len(nodes) != len(optPlatforms) {
+		// if we didn't get a perfect match, we need to boot all drivers
+		allIndexes := make([]int, len(r.nodes))
+		for i := range allIndexes {
+			allIndexes[i] = i
+		}
+
+		clients, err := r.boot(ctx, allIndexes, pw)
+		if err != nil {
+			return nil, err
+		}
+		eg, egCtx := errgroup.WithContext(ctx)
+		workers := make([][]ocispecs.Platform, len(clients))
+		for i, c := range clients {
+			i, c := i, c
+			if c == nil {
+				continue
+			}
+			eg.Go(func() error {
+				ww, err := c.ListWorkers(egCtx)
+				if err != nil {
+					return errors.Wrap(err, "listing workers")
+				}
+
+				ps := make(map[string]ocispecs.Platform, len(ww))
+				for _, w := range ww {
+					for _, p := range w.Platforms {
+						pk := platforms.Format(platforms.Normalize(p))
+						ps[pk] = p
+					}
+				}
+				for _, p := range ps {
+					workers[i] = append(workers[i], p)
+				}
+				return nil
+			})
+		}
+		if err := eg.Wait(); err != nil {
+			return nil, err
+		}
+
+		// then we can attempt to match against all the available platforms
+		// (this time we don't care about imperfect matches)
+		nodes = map[string][]*ResolvedNode{}
+		for k, optPlatforms := range optPlatforms {
+			node, _, err := r.resolve(ctx, optPlatforms, pw, platforms.Only, func(idx int, n builder.Node) []ocispecs.Platform {
+				return workers[idx]
+			})
+			if err != nil {
+				return nil, err
+			}
+			nodes[k] = node
+		}
+	}
+
+	idxs := make([]int, 0, len(r.nodes))
+	for _, nodes := range nodes {
+		for _, node := range nodes {
+			idxs = append(idxs, node.driverIndex)
+		}
+	}
+
+	// preload capabilities
+	span, ctx := tracing.StartSpan(ctx, "load buildkit capabilities", trace.WithSpanKind(trace.SpanKindInternal))
+	_, err := r.opts(ctx, idxs, pw)
+	tracing.FinishWithError(span, err)
+	if err != nil {
+		return nil, err
+	}
+
+	return nodes, nil
+}
+
+func (r *nodeResolver) resolve(ctx context.Context, ps []ocispecs.Platform, pw progress.Writer, matcher matchMaker, additional func(idx int, n builder.Node) []ocispecs.Platform) ([]*ResolvedNode, bool, error) {
+	if len(r.nodes) == 0 {
+		return nil, true, nil
+	}
+
+	perfect := true
+	nodeIdxs := make([]int, 0)
+	for _, p := range ps {
+		idx := r.get(p, matcher, additional)
+		if idx == -1 {
+			idx = 0
+			perfect = false
+		}
+		nodeIdxs = append(nodeIdxs, idx)
+	}
+
+	var nodes []*ResolvedNode
+	if len(nodeIdxs) == 0 {
+		nodes = append(nodes, &ResolvedNode{
+			resolver:    r,
+			driverIndex: 0,
+		})
+		nodeIdxs = append(nodeIdxs, 0)
+	} else {
+		for i, idx := range nodeIdxs {
+			node := &ResolvedNode{
+				resolver:    r,
+				driverIndex: idx,
+			}
+			if len(ps) > 0 {
+				node.platforms = []ocispecs.Platform{ps[i]}
+			}
+			nodes = append(nodes, node)
+		}
+	}
+
+	nodes = recombineNodes(nodes)
+	if _, err := r.boot(ctx, nodeIdxs, pw); err != nil {
+		return nil, false, err
+	}
+	return nodes, perfect, nil
+}
+
+func (r *nodeResolver) get(p ocispecs.Platform, matcher matchMaker, additionalPlatforms func(int, builder.Node) []ocispecs.Platform) int {
+	best := -1
+	bestPlatform := ocispecs.Platform{}
+	for i, node := range r.nodes {
+		platforms := node.Platforms
+		if additionalPlatforms != nil {
+			platforms = slices.Clone(platforms)
+			platforms = append(platforms, additionalPlatforms(i, node)...)
+		}
+		for _, p2 := range platforms {
+			m := matcher(p2)
+			if !m.Match(p) {
+				continue
+			}
+
+			if best == -1 {
+				best = i
+				bestPlatform = p2
+				continue
+			}
+			if matcher(p2).Less(p, bestPlatform) {
+				best = i
+				bestPlatform = p2
+			}
+		}
+	}
+	return best
+}
+
+func (r *nodeResolver) boot(ctx context.Context, idxs []int, pw progress.Writer) ([]*client.Client, error) {
+	clients := make([]*client.Client, len(idxs))
+
+	baseCtx := ctx
+	eg, ctx := errgroup.WithContext(ctx)
+
+	for i, idx := range idxs {
+		i, idx := i, idx
+		eg.Go(func() error {
+			c, err := r.clients.g.Do(ctx, fmt.Sprint(idx), func(ctx context.Context) (*client.Client, error) {
+				if r.nodes[idx].Driver == nil {
+					return nil, nil
+				}
+				r.clients.cacheMu.Lock()
+				c, ok := r.clients.cache[idx]
+				r.clients.cacheMu.Unlock()
+				if ok {
+					return c, nil
+				}
+				c, err := driver.Boot(ctx, baseCtx, r.nodes[idx].Driver, pw)
+				if err != nil {
+					return nil, err
+				}
+				r.clients.cacheMu.Lock()
+				r.clients.cache[idx] = c
+				r.clients.cacheMu.Unlock()
+				return c, nil
+			})
+			if err != nil {
+				return err
+			}
+			clients[i] = c
+			return nil
+		})
+	}
+	if err := eg.Wait(); err != nil {
+		return nil, err
+	}
+
+	return clients, nil
+}
+
+func (r *nodeResolver) opts(ctx context.Context, idxs []int, pw progress.Writer) ([]gateway.BuildOpts, error) {
+	clients, err := r.boot(ctx, idxs, pw)
+	if err != nil {
+		return nil, err
+	}
+
+	bopts := make([]gateway.BuildOpts, len(clients))
+	eg, ctx := errgroup.WithContext(ctx)
+	for i, idxs := range idxs {
+		i, idx := i, idxs
+		c := clients[i]
+		if c == nil {
+			continue
+		}
+		eg.Go(func() error {
+			opt, err := r.buildOpts.g.Do(ctx, fmt.Sprint(idx), func(ctx context.Context) (gateway.BuildOpts, error) {
+				r.buildOpts.cacheMu.Lock()
+				opt, ok := r.buildOpts.cache[idx]
+				r.buildOpts.cacheMu.Unlock()
+				if ok {
+					return opt, nil
+				}
+				_, err := c.Build(ctx, client.SolveOpt{
+					Internal: true,
+				}, "buildx", func(ctx context.Context, c gateway.Client) (*gateway.Result, error) {
+					opt = c.BuildOpts()
+					return nil, nil
+				}, nil)
+				if err != nil {
+					return gateway.BuildOpts{}, err
+				}
+				r.buildOpts.cacheMu.Lock()
+				r.buildOpts.cache[idx] = opt
+				r.buildOpts.cacheMu.Unlock()
+				return opt, err
+			})
+			if err != nil {
+				return err
+			}
+			bopts[i] = opt
+			return nil
+		})
+	}
+	if err := eg.Wait(); err != nil {
+		return nil, err
+	}
+	return bopts, nil
+}
+
+// recombineDriverPairs recombines resolved nodes that are on the same driver
+// back together into a single node.
+func recombineNodes(nodes []*ResolvedNode) []*ResolvedNode {
+	result := make([]*ResolvedNode, 0, len(nodes))
+	lookup := map[int]int{}
+	for _, node := range nodes {
+		if idx, ok := lookup[node.driverIndex]; ok {
+			result[idx].platforms = append(result[idx].platforms, node.platforms...)
+		} else {
+			lookup[node.driverIndex] = len(result)
+			result = append(result, node)
+		}
+	}
+	return result
+}
@@ -0,0 +1,315 @@
+package resolver
+
+import (
+	"context"
+	"sort"
+	"testing"
+
+	"github.com/containerd/platforms"
+	"github.com/docker/buildx/builder"
+	ocispecs "github.com/opencontainers/image-spec/specs-go/v1"
+	"github.com/stretchr/testify/require"
+)
+
+func TestFindDriverSanity(t *testing.T) {
+	r := makeTestResolver(map[string][]ocispecs.Platform{
+		"aaa": {platforms.DefaultSpec()},
+	})
+
+	res, perfect, err := r.resolve(context.TODO(), []ocispecs.Platform{platforms.DefaultSpec()}, nil, platforms.OnlyStrict, nil)
+	require.NoError(t, err)
+	require.True(t, perfect)
+	require.Len(t, res, 1)
+	require.Equal(t, 0, res[0].driverIndex)
+	require.Equal(t, "aaa", res[0].Node().Builder)
+	require.Equal(t, []ocispecs.Platform{platforms.DefaultSpec()}, res[0].Platforms())
+}
+
+func TestFindDriverEmpty(t *testing.T) {
+	r := makeTestResolver(nil)
+
+	res, perfect, err := r.resolve(context.TODO(), []ocispecs.Platform{platforms.DefaultSpec()}, nil, platforms.Only, nil)
+	require.NoError(t, err)
+	require.True(t, perfect)
+	require.Nil(t, res)
+}
+
+func TestFindDriverWeirdName(t *testing.T) {
+	r := makeTestResolver(map[string][]ocispecs.Platform{
+		"aaa": {platforms.MustParse("linux/amd64")},
+		"bbb": {platforms.MustParse("linux/foobar")},
+	})
+
+	// find first platform
+	res, perfect, err := r.resolve(context.TODO(), []ocispecs.Platform{platforms.MustParse("linux/foobar")}, nil, platforms.Only, nil)
+	require.NoError(t, err)
+	require.True(t, perfect)
+	require.Len(t, res, 1)
+	require.Equal(t, 1, res[0].driverIndex)
+	require.Equal(t, "bbb", res[0].Node().Builder)
+}
+
+func TestFindDriverUnknown(t *testing.T) {
+	r := makeTestResolver(map[string][]ocispecs.Platform{
+		"aaa": {platforms.MustParse("linux/amd64")},
+	})
+
+	res, perfect, err := r.resolve(context.TODO(), []ocispecs.Platform{platforms.MustParse("linux/riscv64")}, nil, platforms.Only, nil)
+	require.NoError(t, err)
+	require.False(t, perfect)
+	require.Len(t, res, 1)
+	require.Equal(t, 0, res[0].driverIndex)
+	require.Equal(t, "aaa", res[0].Node().Builder)
+}
+
+func TestSelectNodeSinglePlatform(t *testing.T) {
+	r := makeTestResolver(map[string][]ocispecs.Platform{
+		"aaa": {platforms.MustParse("linux/amd64")},
+		"bbb": {platforms.MustParse("linux/riscv64")},
+	})
+
+	// find first platform
+	res, perfect, err := r.resolve(context.TODO(), []ocispecs.Platform{platforms.MustParse("linux/amd64")}, nil, platforms.Only, nil)
+	require.NoError(t, err)
+	require.True(t, perfect)
+	require.Len(t, res, 1)
+	require.Equal(t, 0, res[0].driverIndex)
+	require.Equal(t, "aaa", res[0].Node().Builder)
+
+	// find second platform
+	res, perfect, err = r.resolve(context.TODO(), []ocispecs.Platform{platforms.MustParse("linux/riscv64")}, nil, platforms.Only, nil)
+	require.NoError(t, err)
+	require.True(t, perfect)
+	require.Len(t, res, 1)
+	require.Equal(t, 1, res[0].driverIndex)
+	require.Equal(t, "bbb", res[0].Node().Builder)
+
+	// find an unknown platform, should match the first driver
+	res, perfect, err = r.resolve(context.TODO(), []ocispecs.Platform{platforms.MustParse("linux/s390x")}, nil, platforms.Only, nil)
+	require.NoError(t, err)
+	require.False(t, perfect)
+	require.Len(t, res, 1)
+	require.Equal(t, 0, res[0].driverIndex)
+	require.Equal(t, "aaa", res[0].Node().Builder)
+}
+
+func TestSelectNodeMultiPlatform(t *testing.T) {
+	r := makeTestResolver(map[string][]ocispecs.Platform{
+		"aaa": {platforms.MustParse("linux/amd64"), platforms.MustParse("linux/arm64")},
+		"bbb": {platforms.MustParse("linux/riscv64")},
+	})
+
+	res, perfect, err := r.resolve(context.TODO(), []ocispecs.Platform{platforms.MustParse("linux/amd64")}, nil, platforms.Only, nil)
+	require.NoError(t, err)
+	require.True(t, perfect)
+	require.Len(t, res, 1)
+	require.Equal(t, 0, res[0].driverIndex)
+	require.Equal(t, "aaa", res[0].Node().Builder)
+
+	res, perfect, err = r.resolve(context.TODO(), []ocispecs.Platform{platforms.MustParse("linux/arm64")}, nil, platforms.Only, nil)
+	require.NoError(t, err)
+	require.True(t, perfect)
+	require.Len(t, res, 1)
+	require.Equal(t, 0, res[0].driverIndex)
+	require.Equal(t, "aaa", res[0].Node().Builder)
+
+	res, perfect, err = r.resolve(context.TODO(), []ocispecs.Platform{platforms.MustParse("linux/riscv64")}, nil, platforms.Only, nil)
+	require.NoError(t, err)
+	require.True(t, perfect)
+	require.Len(t, res, 1)
+	require.Equal(t, 1, res[0].driverIndex)
+	require.Equal(t, "bbb", res[0].Node().Builder)
+}
+
+func TestSelectNodeNonStrict(t *testing.T) {
+	r := makeTestResolver(map[string][]ocispecs.Platform{
+		"aaa": {platforms.MustParse("linux/amd64")},
+		"bbb": {platforms.MustParse("linux/arm64")},
+	})
+
+	// arm64 should match itself
+	res, perfect, err := r.resolve(context.TODO(), []ocispecs.Platform{platforms.MustParse("linux/arm64")}, nil, platforms.Only, nil)
+	require.NoError(t, err)
+	require.True(t, perfect)
+	require.Len(t, res, 1)
+	require.Equal(t, "bbb", res[0].Node().Builder)
+
+	// arm64 may support arm/v8
+	res, perfect, err = r.resolve(context.TODO(), []ocispecs.Platform{platforms.MustParse("linux/arm/v8")}, nil, platforms.Only, nil)
+	require.NoError(t, err)
+	require.True(t, perfect)
+	require.Len(t, res, 1)
+	require.Equal(t, "bbb", res[0].Node().Builder)
+
+	// arm64 may support arm/v7
+	res, perfect, err = r.resolve(context.TODO(), []ocispecs.Platform{platforms.MustParse("linux/arm/v7")}, nil, platforms.Only, nil)
+	require.NoError(t, err)
+	require.True(t, perfect)
+	require.Len(t, res, 1)
+	require.Equal(t, "bbb", res[0].Node().Builder)
+}
+
+func TestSelectNodeNonStrictARM(t *testing.T) {
+	r := makeTestResolver(map[string][]ocispecs.Platform{
+		"aaa": {platforms.MustParse("linux/amd64")},
+		"bbb": {platforms.MustParse("linux/arm64")},
+		"ccc": {platforms.MustParse("linux/arm/v8")},
+	})
+
+	res, perfect, err := r.resolve(context.TODO(), []ocispecs.Platform{platforms.MustParse("linux/arm/v8")}, nil, platforms.Only, nil)
+	require.NoError(t, err)
+	require.True(t, perfect)
+	require.Len(t, res, 1)
+	require.Equal(t, "ccc", res[0].Node().Builder)
+
+	res, perfect, err = r.resolve(context.TODO(), []ocispecs.Platform{platforms.MustParse("linux/arm/v7")}, nil, platforms.Only, nil)
+	require.NoError(t, err)
+	require.True(t, perfect)
+	require.Len(t, res, 1)
+	require.Equal(t, "ccc", res[0].Node().Builder)
+}
+
+func TestSelectNodeNonStrictLower(t *testing.T) {
+	r := makeTestResolver(map[string][]ocispecs.Platform{
+		"aaa": {platforms.MustParse("linux/amd64")},
+		"bbb": {platforms.MustParse("linux/arm/v7")},
+	})
+
+	// v8 can't be built on v7 (so we should select the default)...
+	res, perfect, err := r.resolve(context.TODO(), []ocispecs.Platform{platforms.MustParse("linux/arm/v8")}, nil, platforms.Only, nil)
+	require.NoError(t, err)
+	require.False(t, perfect)
+	require.Len(t, res, 1)
+	require.Equal(t, "aaa", res[0].Node().Builder)
+
+	// ...but v6 can be built on v8
+	res, perfect, err = r.resolve(context.TODO(), []ocispecs.Platform{platforms.MustParse("linux/arm/v6")}, nil, platforms.Only, nil)
+	require.NoError(t, err)
+	require.True(t, perfect)
+	require.Len(t, res, 1)
+	require.Equal(t, "bbb", res[0].Node().Builder)
+}
+
+func TestSelectNodePreferStart(t *testing.T) {
+	r := makeTestResolver(map[string][]ocispecs.Platform{
+		"aaa": {platforms.MustParse("linux/amd64")},
+		"bbb": {platforms.MustParse("linux/riscv64")},
+		"ccc": {platforms.MustParse("linux/riscv64")},
+	})
+
+	res, perfect, err := r.resolve(context.TODO(), []ocispecs.Platform{platforms.MustParse("linux/riscv64")}, nil, platforms.Only, nil)
+	require.NoError(t, err)
+	require.True(t, perfect)
+	require.Len(t, res, 1)
+	require.Equal(t, "bbb", res[0].Node().Builder)
+}
+
+func TestSelectNodePreferExact(t *testing.T) {
+	r := makeTestResolver(map[string][]ocispecs.Platform{
+		"aaa": {platforms.MustParse("linux/arm/v8")},
+		"bbb": {platforms.MustParse("linux/arm/v7")},
+	})
+
+	res, perfect, err := r.resolve(context.TODO(), []ocispecs.Platform{platforms.MustParse("linux/arm/v7")}, nil, platforms.Only, nil)
+	require.NoError(t, err)
+	require.True(t, perfect)
+	require.Len(t, res, 1)
+	require.Equal(t, "bbb", res[0].Node().Builder)
+}
+
+func TestSelectNodeNoPlatform(t *testing.T) {
+	r := makeTestResolver(map[string][]ocispecs.Platform{
+		"aaa": {platforms.MustParse("linux/foobar")},
+		"bbb": {platforms.DefaultSpec()},
+	})
+
+	res, perfect, err := r.resolve(context.TODO(), []ocispecs.Platform{}, nil, platforms.Only, nil)
+	require.NoError(t, err)
+	require.True(t, perfect)
+	require.Len(t, res, 1)
+	require.Equal(t, "aaa", res[0].Node().Builder)
+	require.Empty(t, res[0].Platforms())
+}
+
+func TestSelectNodeAdditionalPlatforms(t *testing.T) {
+	r := makeTestResolver(map[string][]ocispecs.Platform{
+		"aaa": {platforms.MustParse("linux/amd64")},
+		"bbb": {platforms.MustParse("linux/arm/v8")},
+	})
+
+	res, perfect, err := r.resolve(context.TODO(), []ocispecs.Platform{platforms.MustParse("linux/arm/v7")}, nil, platforms.Only, nil)
+	require.NoError(t, err)
+	require.True(t, perfect)
+	require.Len(t, res, 1)
+	require.Equal(t, "bbb", res[0].Node().Builder)
+
+	res, perfect, err = r.resolve(context.TODO(), []ocispecs.Platform{platforms.MustParse("linux/arm/v7")}, nil, platforms.Only, func(idx int, n builder.Node) []ocispecs.Platform {
+		if n.Builder == "aaa" {
+			return []ocispecs.Platform{platforms.MustParse("linux/arm/v7")}
+		}
+		return nil
+	})
+	require.NoError(t, err)
+	require.True(t, perfect)
+	require.Len(t, res, 1)
+	require.Equal(t, "aaa", res[0].Node().Builder)
+}
+
+func TestSplitNodeMultiPlatform(t *testing.T) {
+	r := makeTestResolver(map[string][]ocispecs.Platform{
+		"aaa": {platforms.MustParse("linux/amd64"), platforms.MustParse("linux/arm64")},
+		"bbb": {platforms.MustParse("linux/riscv64")},
+	})
+
+	res, perfect, err := r.resolve(context.TODO(), []ocispecs.Platform{
+		platforms.MustParse("linux/amd64"),
+		platforms.MustParse("linux/arm64"),
+	}, nil, platforms.Only, nil)
+	require.NoError(t, err)
+	require.True(t, perfect)
+	require.Len(t, res, 1)
+	require.Equal(t, "aaa", res[0].Node().Builder)
+
+	res, perfect, err = r.resolve(context.TODO(), []ocispecs.Platform{
+		platforms.MustParse("linux/amd64"),
+		platforms.MustParse("linux/riscv64"),
+	}, nil, platforms.Only, nil)
+	require.NoError(t, err)
+	require.True(t, perfect)
+	require.Len(t, res, 2)
+	require.Equal(t, "aaa", res[0].Node().Builder)
+	require.Equal(t, "bbb", res[1].Node().Builder)
+}
+
+func TestSplitNodeMultiPlatformNoUnify(t *testing.T) {
+	r := makeTestResolver(map[string][]ocispecs.Platform{
+		"aaa": {platforms.MustParse("linux/amd64")},
+		"bbb": {platforms.MustParse("linux/amd64"), platforms.MustParse("linux/riscv64")},
+	})
+
+	// the "best" choice would be the node with both platforms, but we're using
+	// a naive algorithm that doesn't try to unify the platforms
+	res, perfect, err := r.resolve(context.TODO(), []ocispecs.Platform{
+		platforms.MustParse("linux/amd64"),
+		platforms.MustParse("linux/riscv64"),
+	}, nil, platforms.Only, nil)
+	require.NoError(t, err)
+	require.True(t, perfect)
+	require.Len(t, res, 2)
+	require.Equal(t, "aaa", res[0].Node().Builder)
+	require.Equal(t, "bbb", res[1].Node().Builder)
+}
+
+func makeTestResolver(nodes map[string][]ocispecs.Platform) *nodeResolver {
+	var ns []builder.Node
+	for name, platforms := range nodes {
+		ns = append(ns, builder.Node{
+			Builder:   name,
+			Platforms: platforms,
+		})
+	}
+	sort.Slice(ns, func(i, j int) bool {
+		return ns[i].Builder < ns[j].Builder
+	})
+	return newDriverResolver(ns)
+}