[v0.25 backport] fix cache export error handling

cache/remotecache/azblob/importer.go

@@ -11,6 +11,7 @@ import (
 	"github.com/Azure/azure-sdk-for-go/sdk/storage/azblob/container"
 	"github.com/containerd/containerd/v2/core/content"
 	"github.com/containerd/containerd/v2/pkg/labels"
+	cerrdefs "github.com/containerd/errdefs"
 	"github.com/moby/buildkit/cache/remotecache"
 	v1 "github.com/moby/buildkit/cache/remotecache/v1"
 	"github.com/moby/buildkit/session"
@@ -214,7 +215,7 @@ type ciProvider struct {
 
 func (p *ciProvider) Info(ctx context.Context, dgst digest.Digest) (content.Info, error) {
 	if dgst != p.desc.Digest {
-		return content.Info{}, errors.Errorf("content not found %s", dgst)
+		return content.Info{}, errors.Wrapf(cerrdefs.ErrNotFound, "blob %s", dgst)
 	}
 
 	if p.checked {
@@ -234,7 +235,7 @@ func (p *ciProvider) Info(ctx context.Context, dgst digest.Digest) (content.Info
 	}
 
 	if !exists {
-		return content.Info{}, errors.Errorf("blob %s not found", dgst)
+		return content.Info{}, errors.Wrapf(cerrdefs.ErrNotFound, "blob %s", dgst)
 	}
 
 	p.checked = true

cache/remotecache/gha/gha.go

@@ -14,6 +14,7 @@ import (
 
 	"github.com/containerd/containerd/v2/core/content"
 	"github.com/containerd/containerd/v2/pkg/labels"
+	cerrdefs "github.com/containerd/errdefs"
 	"github.com/moby/buildkit/cache/remotecache"
 	v1 "github.com/moby/buildkit/cache/remotecache/v1"
 	"github.com/moby/buildkit/session"
@@ -440,7 +441,7 @@ type ciProvider struct {
 
 func (p *ciProvider) Info(ctx context.Context, dgst digest.Digest) (content.Info, error) {
 	if dgst != p.desc.Digest {
-		return content.Info{}, errors.Errorf("content not found %s", dgst)
+		return content.Info{}, errors.Wrapf(cerrdefs.ErrNotFound, "blob %s", dgst)
 	}
 
 	if _, err := p.loadEntry(ctx, p.desc); err != nil {
@@ -465,7 +466,7 @@ func (p *ciProvider) loadEntry(ctx context.Context, desc ocispecs.Descriptor) (*
 		return nil, err
 	}
 	if ce == nil {
-		return nil, errors.Errorf("blob %s not found", desc.Digest)
+		return nil, errors.Wrapf(cerrdefs.ErrNotFound, "blob %s", desc.Digest)
 	}
 	if p.entries == nil {
 		p.entries = make(map[digest.Digest]*actionscache.Entry)

cache/remotecache/v1/chains.go

@@ -10,6 +10,7 @@ import (
 
 	"github.com/cespare/xxhash/v2"
 	"github.com/containerd/containerd/v2/core/content"
+	cerrdefs "github.com/containerd/errdefs"
 	"github.com/moby/buildkit/session"
 	"github.com/moby/buildkit/solver"
 	digest "github.com/opencontainers/go-digest"
@@ -246,7 +247,7 @@ func (p DescriptorProviderPair) Info(ctx context.Context, dgst digest.Digest) (c
 		return p.InfoProvider.Info(ctx, dgst)
 	}
 	if dgst != p.Descriptor.Digest {
-		return content.Info{}, errors.Errorf("content not found %s", dgst)
+		return content.Info{}, errors.Wrapf(cerrdefs.ErrNotFound, "blob %s", dgst)
 	}
 	return content.Info{
 		Digest: p.Descriptor.Digest,

solver/exporter.go

@@ -5,6 +5,7 @@ import (
 	"errors"
 	"slices"
 
+	cerrdefs "github.com/containerd/errdefs"
 	digest "github.com/opencontainers/go-digest"
 )
 
@@ -189,24 +190,28 @@ func (e *exporter) ExportTo(ctx context.Context, t CacheExporterTarget, opt Cach
 		if (remote == nil || opt.CompressionOpt != nil) && opt.Mode != CacheExportModeRemoteOnly {
 			res, err := cm.results.Load(ctx, res)
 			if err != nil {
-				return nil, err
-			}
-			remotes, err := opt.ResolveRemotes(ctx, res)
-			if err != nil {
-				return nil, err
-			}
-			res.Release(context.TODO())
-			if remote == nil && len(remotes) > 0 {
-				remote, remotes = remotes[0], remotes[1:] // pop the first element
-			}
-			if opt.CompressionOpt != nil {
-				for _, r := range remotes { // record all remaining remotes as well
-					results = append(results, CacheExportResult{
-						CreatedAt:  v.CreatedAt,
-						Result:     r,
-						EdgeVertex: k.vtx,
-						EdgeIndex:  k.output,
-					})
+				if !errors.Is(err, cerrdefs.ErrNotFound) {
+					return nil, err
+				}
+				remote = nil
+			} else {
+				remotes, err := opt.ResolveRemotes(ctx, res)
+				if err != nil {
+					return nil, err
+				}
+				res.Release(context.TODO())
+				if remote == nil && len(remotes) > 0 {
+					remote, remotes = remotes[0], remotes[1:] // pop the first element
+				}
+				if opt.CompressionOpt != nil {
+					for _, r := range remotes { // record all remaining remotes as well
+						results = append(results, CacheExportResult{
+							CreatedAt:  v.CreatedAt,
+							Result:     r,
+							EdgeVertex: k.vtx,
+							EdgeIndex:  k.output,
+						})
+					}
 				}
 			}
 		}
@@ -232,7 +237,7 @@ func (e *exporter) ExportTo(ctx context.Context, t CacheExporterTarget, opt Cach
 		for _, dep := range deps {
 			rec, err := dep.CacheKey.Exporter.ExportTo(ctx, t, opt)
 			if err != nil {
-				return nil, err
+				continue
 			}
 			for _, r := range rec {
 				srcs[i] = append(srcs[i], CacheLink{Src: r, Selector: string(dep.Selector)})
@@ -244,7 +249,7 @@ func (e *exporter) ExportTo(ctx context.Context, t CacheExporterTarget, opt Cach
 		for _, de := range e.edge.secondaryExporters {
 			recs, err := de.cacheKey.CacheKey.Exporter.ExportTo(mainCtx, t, opt)
 			if err != nil {
-				return nil, nil
+				continue
 			}
 			for _, r := range recs {
 				srcs[de.index] = append(srcs[de.index], CacheLink{Src: r, Selector: de.cacheKey.Selector.String()})
@@ -261,6 +266,14 @@ func (e *exporter) ExportTo(ctx context.Context, t CacheExporterTarget, opt Cach
 		}
 	}
 
+	// validate deps are present
+	for _, deps := range srcs {
+		if len(deps) == 0 {
+			res[e] = nil
+			return res[e], nil
+		}
+	}
+
 	if v != nil && len(deps) == 0 {
 		cm := v.cacheManager
 		key := cm.getID(v.key)