Fixes to nil results for multi-platform builds

exporter/oci/export.go

@@ -236,6 +236,9 @@ func (e *imageExporterInstance) Export(ctx context.Context, src *exporter.Source
 	mprovider := contentutil.NewMultiProvider(e.opt.ImageWriter.ContentStore())
 	for _, ref := range refs {
 		eg.Go(func() error {
+			if ref == nil {
+				return nil
+			}
 			remotes, err := ref.GetRemotes(egCtx, false, e.opts.RefCfg, false, session.NewGroup(sessionID))
 			if err != nil {
 				return err

frontend/dockerfile/dockerfile_provenance_test.go

@@ -1055,22 +1055,59 @@ ENV FOO=bar
 		t,
 		fstest.CreateFile("Dockerfile", dockerfile, 0600),
 	)
-
-	_, err = f.Solve(sb.Context(), c, client.SolveOpt{
-		LocalMounts: map[string]fsutil.FS{
-			dockerui.DefaultLocalNameDockerfile: dir,
-			dockerui.DefaultLocalNameContext:    dir,
-		},
-		FrontendAttrs: map[string]string{
-			"attest:provenance": "mode=max",
-		},
-		Exports: []client.ExportEntry{
-			{
+	buf := &bytes.Buffer{}
+
+	exporters := []struct {
+		name   string
+		export client.ExportEntry
+	}{
+		{
+			name: "image",
+			export: client.ExportEntry{
 				Type: client.ExporterImage,
 			},
 		},
-	}, nil)
-	require.NoError(t, err)
+		{
+			name: "local",
+			export: client.ExportEntry{
+				Type:      client.ExporterLocal,
+				OutputDir: t.TempDir(),
+			},
+		},
+		{
+			name: "tar",
+			export: func() client.ExportEntry {
+				return client.ExportEntry{
+					Type:   client.ExporterTar,
+					Output: fixedWriteCloser(&nopWriteCloser{buf}),
+				}
+			}(),
+		},
+	}
+
+	for _, exp := range exporters {
+		for _, platformMode := range []string{"single", "multi"} {
+			t.Run(exp.name+"/"+platformMode, func(t *testing.T) {
+				attrs := map[string]string{
+					"attest:provenance": "mode=max",
+				}
+				if platformMode == "multi" {
+					attrs["platform"] = "linux/amd64,linux/arm64"
+				}
+				_, err = f.Solve(sb.Context(), c, client.SolveOpt{
+					LocalMounts: map[string]fsutil.FS{
+						dockerui.DefaultLocalNameDockerfile: dir,
+						dockerui.DefaultLocalNameContext:    dir,
+					},
+					FrontendAttrs: attrs,
+					Exports: []client.ExportEntry{
+						exp.export,
+					},
+				}, nil)
+				require.NoError(t, err)
+			})
+		}
+	}
 }
 
 // https://github.com/moby/buildkit/issues/3562

frontend/dockerfile/dockerfile_test.go

@@ -201,6 +201,7 @@ var allTests = integration.TestFuncs(
 	testDockerIgnoreMissingProvenance,
 	testCommandSourceMapping,
 	testSBOMScannerArgs,
+	testMultiNilRefsOCIExporter,
 	testNilContextInSolveGateway,
 	testMultiNilRefsInSolveGateway,
 	testCopyUnicodePath,
@@ -9237,6 +9238,66 @@ COPY --link foo foo
 	}
 }
 
+func testMultiNilRefsOCIExporter(t *testing.T, sb integration.Sandbox) {
+	integration.SkipOnPlatform(t, "windows")
+	workers.CheckFeatureCompat(t, sb, workers.FeatureMultiPlatform, workers.FeatureOCIExporter)
+
+	f := getFrontend(t, sb)
+
+	dockerfile := []byte(`FROM scratch`)
+
+	dir := integration.Tmpdir(
+		t,
+		fstest.CreateFile("Dockerfile", dockerfile, 0600),
+	)
+
+	c, err := client.New(sb.Context(), sb.Address())
+	require.NoError(t, err)
+	defer c.Close()
+
+	destDir := t.TempDir()
+
+	out := filepath.Join(destDir, "out.tar")
+	outW, err := os.Create(out)
+	require.NoError(t, err)
+
+	_, err = f.Solve(sb.Context(), c, client.SolveOpt{
+		LocalMounts: map[string]fsutil.FS{
+			dockerui.DefaultLocalNameDockerfile: dir,
+			dockerui.DefaultLocalNameContext:    dir,
+		},
+		FrontendAttrs: map[string]string{
+			"platform": "linux/arm64,linux/amd64",
+		},
+		Exports: []client.ExportEntry{
+			{
+				Type:   client.ExporterOCI,
+				Output: fixedWriteCloser(outW),
+			},
+		},
+	}, nil)
+	require.NoError(t, err)
+
+	dt, err := os.ReadFile(filepath.Join(destDir, "out.tar"))
+	require.NoError(t, err)
+
+	m, err := testutil.ReadTarToMap(dt, false)
+	require.NoError(t, err)
+
+	var idx ocispecs.Index
+	err = json.Unmarshal(m[ocispecs.ImageIndexFile].Data, &idx)
+	require.NoError(t, err)
+
+	require.Equal(t, 1, len(idx.Manifests))
+	mlistHex := idx.Manifests[0].Digest.Hex()
+
+	idx = ocispecs.Index{}
+	err = json.Unmarshal(m[ocispecs.ImageBlobsDir+"/sha256/"+mlistHex].Data, &idx)
+	require.NoError(t, err)
+
+	require.Equal(t, 2, len(idx.Manifests))
+}
+
 func timeMustParse(t *testing.T, layout, value string) time.Time {
 	tm, err := time.Parse(layout, value)
 	require.NoError(t, err)

solver/llbsolver/solver.go

@@ -933,6 +933,7 @@ func addProvenanceToResult(res *frontend.Result, br *provenanceBridge) (*Result,
 	}
 	for k, ref := range res.Refs {
 		if ref == nil {
+			out.Provenance.Refs[k] = nil
 			continue
 		}
 		cp, err := getProvenance(ref, reqs.refs[k].bridge, k, reqs)