Add a new MutableResult type to solver/result package that implements

thread-safe Result.
Address review comments:
 * Re-use the input variable in exporters to avoid accidental re-use of
   stale values

exporter/containerimage/export.go

@@ -187,21 +187,19 @@ func (e *imageExporterInstance) Config() *exporter.Config {
 	return exporter.NewConfigWithCompression(e.opts.RefCfg.Compression)
 }
 
-func (e *imageExporterInstance) Export(ctx context.Context, src *exporter.Source, sessionID string) (map[string]string, exporter.DescriptorReference, error) {
+func (e *imageExporterInstance) Export(ctx context.Context, src exporter.Source, sessionID string) (map[string]string, exporter.DescriptorReference, error) {
 	return e.ExportImage(ctx, src, exptypes.InlineCache{}, sessionID)
 }
 
-func (e *imageExporterInstance) ExportImage(ctx context.Context, src *exporter.Source, inlineCache exptypes.InlineCache, sessionID string) (_ map[string]string, descref exporter.DescriptorReference, err error) {
+func (e *imageExporterInstance) ExportImage(ctx context.Context, src exporter.Source, inlineCache exptypes.InlineCache, sessionID string) (_ map[string]string, descref exporter.DescriptorReference, err error) {
 	meta := make(map[string][]byte)
 	for k, v := range src.Metadata {
 		meta[k] = v
 	}
 	for k, v := range e.meta {
 		meta[k] = v
 	}
-	inp := *src
-	inp.Metadata = meta
-	src = &inp
+	src.Metadata = meta
 
 	opts := e.opts
 	as, _, err := ParseAnnotations(meta)
@@ -221,7 +219,7 @@ func (e *imageExporterInstance) ExportImage(ctx context.Context, src *exporter.S
 		}
 	}()
 
-	desc, err := e.opt.ImageWriter.Commit(ctx, src, sessionID, &opts)
+	desc, err := e.opt.ImageWriter.Commit(ctx, &src, sessionID, &opts)
 	if err != nil {
 		return nil, nil, err
 	}
@@ -283,7 +281,7 @@ func (e *imageExporterInstance) ExportImage(ctx context.Context, src *exporter.S
 				tagDone(nil)
 
 				if e.unpack {
-					if err := e.unpackImage(ctx, img, src, session.NewGroup(sessionID)); err != nil {
+					if err := e.unpackImage(ctx, img, &src, session.NewGroup(sessionID)); err != nil {
 						return nil, nil, err
 					}
 				}
@@ -319,7 +317,7 @@ func (e *imageExporterInstance) ExportImage(ctx context.Context, src *exporter.S
 				}
 			}
 			if e.push {
-				err := e.pushImage(ctx, src, sessionID, targetName, desc.Digest)
+				err := e.pushImage(ctx, &src, sessionID, targetName, desc.Digest)
 				if err != nil {
 					return nil, nil, errors.Wrapf(err, "failed to push %v", targetName)
 				}

exporter/exporter.go

@@ -20,7 +20,7 @@ type Exporter interface {
 type ExporterInstance interface {
 	Name() string
 	Config() *Config
-	Export(ctx context.Context, src *Source, sessionID string) (map[string]string, DescriptorReference, error)
+	Export(ctx context.Context, src Source, sessionID string) (map[string]string, DescriptorReference, error)
 }
 
 type DescriptorReference interface {

exporter/local/export.go

@@ -60,12 +60,12 @@ func (e *localExporter) Config() *exporter.Config {
 	return exporter.NewConfig()
 }
 
-func (e *localExporterInstance) Export(ctx context.Context, inp *exporter.Source, sessionID string) (map[string]string, exporter.DescriptorReference, error) {
+func (e *localExporterInstance) Export(ctx context.Context, inp exporter.Source, sessionID string) (map[string]string, exporter.DescriptorReference, error) {
 	timeoutCtx, cancel := context.WithTimeout(ctx, 5*time.Second)
 	defer cancel()
 
 	if e.opts.Epoch == nil {
-		if tm, ok, err := epoch.ParseSource(inp); err != nil {
+		if tm, ok, err := epoch.ParseSource(&inp); err != nil {
 			return nil, nil, err
 		} else if ok {
 			e.opts.Epoch = tm

exporter/oci/export.go

@@ -113,11 +113,11 @@ func (e *imageExporterInstance) Config() *exporter.Config {
 	return exporter.NewConfigWithCompression(e.opts.RefCfg.Compression)
 }
 
-func (e *imageExporterInstance) Export(ctx context.Context, src *exporter.Source, sessionID string) (map[string]string, exporter.DescriptorReference, error) {
+func (e *imageExporterInstance) Export(ctx context.Context, src exporter.Source, sessionID string) (map[string]string, exporter.DescriptorReference, error) {
 	return e.ExportImage(ctx, src, exptypes.InlineCache{}, sessionID)
 }
 
-func (e *imageExporterInstance) ExportImage(ctx context.Context, src *exporter.Source, inlineCache exptypes.InlineCache, sessionID string) (_ map[string]string, descref exporter.DescriptorReference, err error) {
+func (e *imageExporterInstance) ExportImage(ctx context.Context, src exporter.Source, inlineCache exptypes.InlineCache, sessionID string) (_ map[string]string, descref exporter.DescriptorReference, err error) {
 	if e.opt.Variant == VariantDocker && len(src.Refs) > 0 {
 		return nil, nil, errors.Errorf("docker exporter does not currently support exporting manifest lists")
 	}
@@ -129,9 +129,7 @@ func (e *imageExporterInstance) ExportImage(ctx context.Context, src *exporter.S
 	for k, v := range e.meta {
 		meta[k] = v
 	}
-	inp := *src
-	inp.Metadata = meta
-	src = &inp
+	src.Metadata = meta
 
 	opts := e.opts
 	as, _, err := containerimage.ParseAnnotations(meta)
@@ -151,7 +149,7 @@ func (e *imageExporterInstance) ExportImage(ctx context.Context, src *exporter.S
 		}
 	}()
 
-	desc, err := e.opt.ImageWriter.Commit(ctx, src, sessionID, &opts)
+	desc, err := e.opt.ImageWriter.Commit(ctx, &src, sessionID, &opts)
 	if err != nil {
 		return nil, nil, err
 	}

exporter/tar/export.go

@@ -58,7 +58,7 @@ func (e *localExporterInstance) Config() *exporter.Config {
 	return exporter.NewConfig()
 }
 
-func (e *localExporterInstance) Export(ctx context.Context, inp *exporter.Source, sessionID string) (map[string]string, exporter.DescriptorReference, error) {
+func (e *localExporterInstance) Export(ctx context.Context, inp exporter.Source, sessionID string) (map[string]string, exporter.DescriptorReference, error) {
 	var defers []func() error
 
 	defer func() {
@@ -68,7 +68,7 @@ func (e *localExporterInstance) Export(ctx context.Context, inp *exporter.Source
 	}()
 
 	if e.opts.Epoch == nil {
-		if tm, ok, err := epoch.ParseSource(inp); err != nil {
+		if tm, ok, err := epoch.ParseSource(&inp); err != nil {
 			return nil, nil, err
 		} else if ok {
 			e.opts.Epoch = tm

frontend/dockerui/build.go

@@ -4,7 +4,6 @@ import (
 	"context"
 	"encoding/json"
 	"fmt"
-	"sync"
 
 	"github.com/containerd/containerd/platforms"
 	"github.com/moby/buildkit/exporter/containerimage/exptypes"
@@ -18,7 +17,7 @@ import (
 type BuildFunc func(ctx context.Context, platform *ocispecs.Platform, idx int) (client.Reference, *image.Image, error)
 
 func (bc *Client) Build(ctx context.Context, fn BuildFunc) (*ResultBuilder, error) {
-	res := &mutableResult{res: client.NewResult()}
+	res := client.NewMutableResult()
 
 	targets := make([]*ocispecs.Platform, 0, len(bc.TargetPlatforms))
 	for _, p := range bc.TargetPlatforms {
@@ -66,11 +65,11 @@ func (bc *Client) Build(ctx context.Context, fn BuildFunc) (*ResultBuilder, erro
 			k := platforms.Format(p)
 
 			if bc.MultiPlatformRequested {
-				res.addRef(k, ref)
-				res.addMeta(fmt.Sprintf("%s/%s", exptypes.ExporterImageConfigKey, k), config)
+				res.AddRef(k, ref)
+				res.AddMeta(fmt.Sprintf("%s/%s", exptypes.ExporterImageConfigKey, k), config)
 			} else {
-				res.setRef(ref)
-				res.addMeta(exptypes.ExporterImageConfigKey, config)
+				res.SetRef(ref)
+				res.AddMeta(exptypes.ExporterImageConfigKey, config)
 			}
 			expPlatforms.Platforms[i] = exptypes.Platform{
 				ID:       k,
@@ -83,7 +82,7 @@ func (bc *Client) Build(ctx context.Context, fn BuildFunc) (*ResultBuilder, erro
 		return nil, err
 	}
 	return &ResultBuilder{
-		Result:       res.res,
+		Result:       res.Result(),
 		expPlatforms: expPlatforms,
 	}, nil
 }
@@ -113,26 +112,3 @@ func (rb *ResultBuilder) EachPlatform(ctx context.Context, fn func(ctx context.C
 	}
 	return eg.Wait()
 }
-
-func (r *mutableResult) addMeta(k string, v []byte) {
-	r.mu.Lock()
-	r.res.AddMeta(k, v)
-	r.mu.Unlock()
-}
-
-func (r *mutableResult) addRef(k string, ref client.Reference) {
-	r.mu.Lock()
-	r.res.AddRef(k, ref)
-	r.mu.Unlock()
-}
-
-func (r *mutableResult) setRef(ref client.Reference) {
-	r.mu.Lock()
-	r.res.SetRef(ref)
-	r.mu.Unlock()
-}
-
-type mutableResult struct {
-	mu  sync.Mutex
-	res *client.Result
-}

frontend/gateway/client/client.go

@@ -16,6 +16,7 @@ import (
 )
 
 type Result = result.Result[Reference]
+type MutableResult = result.MutableResult[Reference]
 
 type Attestation = result.Attestation[Reference]
 
@@ -25,6 +26,10 @@ func NewResult() *Result {
 	return &Result{}
 }
 
+func NewMutableResult() *MutableResult {
+	return &MutableResult{}
+}
+
 type Client interface {
 	Solve(ctx context.Context, req SolveRequest) (*Result, error)
 	ResolveImageConfig(ctx context.Context, ref string, opt llb.ResolveImageConfigOpt) (string, digest.Digest, []byte, error)

solver/llbsolver/solver.go

@@ -552,12 +552,12 @@ func (s *Solver) Solve(ctx context.Context, id string, sessionID string, req fro
 
 	cacheExporters, inlineCacheExporter := splitCacheExporters(exp.CacheExporters)
 	var exporterResponse map[string]string
-	exporterResponse, descref, err = s.runExporters(ctx, exp.Exporters, inlineCacheExporter, j, cached, inp)
+	exporterResponse, descref, err = s.runExporters(ctx, exp.Exporters, inlineCacheExporter, j, *cached, *inp)
 	if err != nil {
 		return nil, err
 	}
 
-	cacheExporterResponse, err := runCacheExporters(ctx, cacheExporters, j, cached, inp)
+	cacheExporterResponse, err := runCacheExporters(ctx, cacheExporters, j, *cached, *inp)
 	if err != nil {
 		return nil, err
 	}
@@ -582,7 +582,7 @@ func (s *Solver) Solve(ctx context.Context, id string, sessionID string, req fro
 	}, nil
 }
 
-func runCacheExporters(ctx context.Context, exporters []RemoteCacheExporter, j *solver.Job, cached *result.Result[solver.CachedResult], inp *result.Result[cache.ImmutableRef]) (map[string]string, error) {
+func runCacheExporters(ctx context.Context, exporters []RemoteCacheExporter, j *solver.Job, cached result.Result[solver.CachedResult], inp result.Result[cache.ImmutableRef]) (map[string]string, error) {
 	eg, ctx := errgroup.WithContext(ctx)
 	g := session.NewGroup(j.SessionID)
 	var cacheExporterResponse map[string]string
@@ -593,7 +593,7 @@ func runCacheExporters(ctx context.Context, exporters []RemoteCacheExporter, j *
 				id := fmt.Sprint(j.SessionID, "-cache-", i)
 				err = inBuilderContext(ctx, j, exp.Exporter.Name(), id, func(ctx context.Context, _ session.Group) error {
 					prepareDone := progress.OneOff(ctx, "preparing build cache for export")
-					if err := result.EachRef(cached, inp, func(res solver.CachedResult, ref cache.ImmutableRef) error {
+					if err := result.EachRef(&cached, &inp, func(res solver.CachedResult, ref cache.ImmutableRef) error {
 						ctx = withDescHandlerCacheOpts(ctx, ref)
 
 						// Configure compression
@@ -634,40 +634,37 @@ func runCacheExporters(ctx context.Context, exporters []RemoteCacheExporter, j *
 	return cacheExporterResponse, nil
 }
 
-func runInlineCacheExporter(ctx context.Context, e exporter.ExporterInstance, inlineExporter inlineCacheExporter, j *solver.Job, cached *result.Result[solver.CachedResult]) (result *exptypes.InlineCache, err error) {
+func runInlineCacheExporter(ctx context.Context, e exporter.ExporterInstance, inlineExporter inlineCacheExporter, j *solver.Job, cached result.Result[solver.CachedResult]) (result *exptypes.InlineCache, err error) {
 	result = &exptypes.InlineCache{
 		Platforms: make(map[string][]byte),
 	}
 	if inlineExporter == nil {
 		return result, nil
 	}
 	if err := inBuilderContext(ctx, j, "preparing layers for inline cache", j.SessionID+"-cache-inline", func(ctx context.Context, _ session.Group) error {
-		if res := cached.Ref; res != nil {
+		err := cached.EachPlatformRef(func(platformID string, res solver.CachedResult) error {
 			dtic, err := inlineCache(ctx, inlineExporter, res, e.Config().Compression(), session.NewGroup(j.SessionID))
 			if err != nil {
 				return err
 			}
-			if dtic != nil {
-				result.Cache = dtic
-			}
-		}
-		for k, res := range cached.Refs {
-			dtic, err := inlineCache(ctx, inlineExporter, res, e.Config().Compression(), session.NewGroup(j.SessionID))
-			if err != nil {
-				return err
+			if dtic == nil {
+				return nil
 			}
-			if dtic != nil {
-				result.Platforms[k] = dtic
+			if platformID == "" {
+				result.Cache = dtic
+			} else {
+				result.Platforms[platformID] = dtic
 			}
-		}
-		return nil
+			return nil
+		})
+		return err
 	}); err != nil {
 		return nil, err
 	}
 	return result, nil
 }
 
-func (s *Solver) runExporters(ctx context.Context, exporters []exporter.ExporterInstance, inlineCacheExporter inlineCacheExporter, job *solver.Job, cached *result.Result[solver.CachedResult], inp *result.Result[cache.ImmutableRef]) (exporterResponse map[string]string, descref exporter.DescriptorReference, err error) {
+func (s *Solver) runExporters(ctx context.Context, exporters []exporter.ExporterInstance, inlineCacheExporter inlineCacheExporter, job *solver.Job, cached result.Result[solver.CachedResult], inp result.Result[cache.ImmutableRef]) (exporterResponse map[string]string, descref exporter.DescriptorReference, err error) {
 	eg, ctx := errgroup.WithContext(ctx)
 	sessionID := job.SessionID
 	resps := make([]map[string]string, len(exporters))
@@ -863,7 +860,7 @@ func getProvenance(ref solver.ResultProxy, br *provenanceBridge, id string, reqs
 
 type imageExporterInstance interface {
 	exporter.ExporterInstance
-	ExportImage(ctx context.Context, src *exporter.Source, cache exptypes.InlineCache, sessionID string) (map[string]string, exporter.DescriptorReference, error)
+	ExportImage(ctx context.Context, src exporter.Source, cache exptypes.InlineCache, sessionID string) (map[string]string, exporter.DescriptorReference, error)
 }
 
 func asImageExporter(e exporter.ExporterInstance) (imageExporterInstance, bool) {

solver/result/result.go

@@ -1,6 +1,8 @@
 package result
 
 import (
+	"sync"
+
 	"github.com/pkg/errors"
 )
 
@@ -85,6 +87,33 @@ func (r *Result[T]) EachRef(fn func(T) error) (err error) {
 	return err
 }
 
+// EachPlatformRef iterates through all underlying refs and invokes
+// the given handler with the platform ID corresponding to the ref.
+// For the single ref case, the platform ID is an empty string.
+func (r *Result[T]) EachPlatformRef(fn func(string, T) error) (err error) {
+	var zero T
+	if r.Ref != zero {
+		err = fn("", r.Ref)
+	}
+	for p, r := range r.Refs {
+		if r != zero {
+			if err1 := fn(p, r); err1 != nil && err == nil {
+				err = err1
+			}
+		}
+	}
+	for p, as := range r.Attestations {
+		for _, a := range as {
+			if a.Ref != zero {
+				if err1 := fn(p, a.Ref); err1 != nil && err == nil {
+					err = err1
+				}
+			}
+		}
+	}
+	return err
+}
+
 // EachRef iterates over references in both a and b.
 // a and b are assumed to be of the same size and map their references
 // to the same set of keys
@@ -170,3 +199,35 @@ func ConvertResult[U comparable, V comparable](r *Result[U], fn func(U) (V, erro
 
 	return r2, nil
 }
+
+// Result returns the underlying Result value
+func (r *MutableResult[T]) Result() *Result[T] {
+	return &r.res
+}
+
+// AddMeta adds the metadata specified with the given key/value pair
+func (r *MutableResult[T]) AddMeta(k string, v []byte) {
+	r.mu.Lock()
+	r.res.AddMeta(k, v)
+	r.mu.Unlock()
+}
+
+// AddRef adds the specified reference for the platform given with k
+func (r *MutableResult[T]) AddRef(k string, ref T) {
+	r.mu.Lock()
+	r.res.AddRef(k, ref)
+	r.mu.Unlock()
+}
+
+// SetRef sets the specified reference as the single reference
+func (r *MutableResult[T]) SetRef(ref T) {
+	r.mu.Lock()
+	r.res.SetRef(ref)
+	r.mu.Unlock()
+}
+
+// MutableResult is a thread-safe version of Result
+type MutableResult[T comparable] struct {
+	mu  sync.Mutex
+	res Result[T]
+}