Add Evaluate(Ref) Gateway API

client/build.go

@@ -113,6 +113,19 @@ func (g *gatewayClientForBuild) StatFile(ctx context.Context, in *gatewayapi.Sta
 	return g.gateway.StatFile(ctx, in, opts...)
 }
 
+func (g *gatewayClientForBuild) Evaluate(ctx context.Context, in *gatewayapi.EvaluateRequest, opts ...grpc.CallOption) (*gatewayapi.EvaluateResponse, error) {
+	if err := g.caps.Supports(gatewayapi.CapGatewayEvaluate); err != nil {
+		if err2 := g.caps.Supports(gatewayapi.CapStatFile); err2 != nil {
+			return nil, err
+		}
+		ctx = buildid.AppendToOutgoingContext(ctx, g.buildID)
+		_, err := g.gateway.StatFile(ctx, &gatewayapi.StatFileRequest{Ref: in.Ref, Path: "."}, opts...)
+		return &gatewayapi.EvaluateResponse{}, err
+	}
+	ctx = buildid.AppendToOutgoingContext(ctx, g.buildID)
+	return g.gateway.Evaluate(ctx, in, opts...)
+}
+
 func (g *gatewayClientForBuild) Ping(ctx context.Context, in *gatewayapi.PingRequest, opts ...grpc.CallOption) (*gatewayapi.PongResponse, error) {
 	ctx = buildid.AppendToOutgoingContext(ctx, g.buildID)
 	return g.gateway.Ping(ctx, in, opts...)

control/gateway/gateway.go

@@ -111,6 +111,14 @@ func (gwf *GatewayForwarder) ReadFile(ctx context.Context, req *gwapi.ReadFileRe
 	return fwd.ReadFile(ctx, req)
 }
 
+func (gwf *GatewayForwarder) Evaluate(ctx context.Context, req *gwapi.EvaluateRequest) (*gwapi.EvaluateResponse, error) {
+	fwd, err := gwf.lookupForwarder(ctx)
+	if err != nil {
+		return nil, errors.Wrap(err, "forwarding Evaluate")
+	}
+	return fwd.Evaluate(ctx, req)
+}
+
 func (gwf *GatewayForwarder) Ping(ctx context.Context, req *gwapi.PingRequest) (*gwapi.PongResponse, error) {
 	fwd, err := gwf.lookupForwarder(ctx)
 	if err != nil {

frontend/frontend_test.go

@@ -31,6 +31,7 @@ func TestFrontendIntegration(t *testing.T) {
 		testRefReadFile,
 		testRefReadDir,
 		testRefStatFile,
+		testRefEvaluate,
 		testReturnNil,
 	))
 }
@@ -291,6 +292,55 @@ func testRefStatFile(t *testing.T, sb integration.Sandbox) {
 	require.NoError(t, err)
 }
 
+func testRefEvaluate(t *testing.T, sb integration.Sandbox) {
+	ctx := sb.Context()
+
+	c, err := client.New(ctx, sb.Address())
+	require.NoError(t, err)
+	defer c.Close()
+
+	frontend := func(ctx context.Context, c gateway.Client) (*gateway.Result, error) {
+		st := llb.Scratch().File(llb.Mkfile("/test", 0666, []byte{}))
+		def, err := st.Marshal(ctx)
+		if err != nil {
+			return nil, err
+		}
+		res, err := c.Solve(ctx, gateway.SolveRequest{
+			Definition: def.ToPB(),
+		})
+		if err != nil {
+			return nil, err
+		}
+		ref, err := res.SingleRef()
+		if err != nil {
+			return nil, err
+		}
+
+		st = llb.Scratch().File(llb.Mkfile("/test/dir-does-not-exist", 0666, []byte{}))
+		def, err = st.Marshal(ctx)
+		if err != nil {
+			return nil, err
+		}
+		res, err = c.Solve(ctx, gateway.SolveRequest{
+			Definition: def.ToPB(),
+		})
+		if err != nil {
+			return nil, err
+		}
+		ref2, err := res.SingleRef()
+		if err != nil {
+			return nil, err
+		}
+
+		require.NoError(t, ref.Evaluate(ctx))
+		require.Error(t, ref2.Evaluate(ctx))
+		return gateway.NewResult(), nil
+	}
+
+	_, err = c.Build(ctx, client.SolveOpt{}, "", frontend, nil)
+	require.NoError(t, err)
+}
+
 func tmpdir(t *testing.T, appliers ...fstest.Applier) (string, error) {
 	tmpdir := t.TempDir()
 	if err := fstest.Apply(appliers...).Apply(tmpdir); err != nil {

frontend/gateway/client/client.go

@@ -91,6 +91,7 @@ type ContainerProcess interface {
 
 type Reference interface {
 	ToState() (llb.State, error)
+	Evaluate(ctx context.Context) error
 	ReadFile(ctx context.Context, req ReadRequest) ([]byte, error)
 	StatFile(ctx context.Context, req StatRequest) (*fstypes.Stat, error)
 	ReadDir(ctx context.Context, req ReadDirRequest) ([]*fstypes.Stat, error)

frontend/gateway/forwarder/forward.go

@@ -318,6 +318,14 @@ func (r *ref) ToState() (st llb.State, err error) {
 	return llb.NewState(defop), nil
 }
 
+func (r *ref) Evaluate(ctx context.Context) error {
+	_, err := r.resultProxy.Result(ctx)
+	if err != nil {
+		return r.c.wrapSolveError(err)
+	}
+	return nil
+}
+
 func (r *ref) ReadFile(ctx context.Context, req client.ReadRequest) ([]byte, error) {
 	m, err := r.getMountable(ctx)
 	if err != nil {

frontend/gateway/gateway.go

@@ -754,15 +754,15 @@ func (lbf *llbBridgeForwarder) Solve(ctx context.Context, req *pb.SolveRequest)
 	return resp, nil
 }
 
-func (lbf *llbBridgeForwarder) getImmutableRef(ctx context.Context, id, path string) (cache.ImmutableRef, error) {
+func (lbf *llbBridgeForwarder) getImmutableRef(ctx context.Context, id string) (cache.ImmutableRef, error) {
 	lbf.mu.Lock()
 	ref, ok := lbf.refs[id]
 	lbf.mu.Unlock()
 	if !ok {
-		return nil, errors.Errorf("no such ref: %v", id)
+		return nil, errors.Errorf("no such ref: %s", id)
 	}
 	if ref == nil {
-		return nil, errors.Wrap(os.ErrNotExist, path)
+		return nil, errors.Errorf("empty ref: %s", id)
 	}
 
 	r, err := ref.Result(ctx)
@@ -781,7 +781,7 @@ func (lbf *llbBridgeForwarder) getImmutableRef(ctx context.Context, id, path str
 func (lbf *llbBridgeForwarder) ReadFile(ctx context.Context, req *pb.ReadFileRequest) (*pb.ReadFileResponse, error) {
 	ctx = tracing.ContextWithSpanFromContext(ctx, lbf.callCtx)
 
-	ref, err := lbf.getImmutableRef(ctx, req.Ref, req.FilePath)
+	ref, err := lbf.getImmutableRef(ctx, req.Ref)
 	if err != nil {
 		return nil, err
 	}
@@ -812,7 +812,7 @@ func (lbf *llbBridgeForwarder) ReadFile(ctx context.Context, req *pb.ReadFileReq
 func (lbf *llbBridgeForwarder) ReadDir(ctx context.Context, req *pb.ReadDirRequest) (*pb.ReadDirResponse, error) {
 	ctx = tracing.ContextWithSpanFromContext(ctx, lbf.callCtx)
 
-	ref, err := lbf.getImmutableRef(ctx, req.Ref, req.DirPath)
+	ref, err := lbf.getImmutableRef(ctx, req.Ref)
 	if err != nil {
 		return nil, err
 	}
@@ -836,7 +836,7 @@ func (lbf *llbBridgeForwarder) ReadDir(ctx context.Context, req *pb.ReadDirReque
 func (lbf *llbBridgeForwarder) StatFile(ctx context.Context, req *pb.StatFileRequest) (*pb.StatFileResponse, error) {
 	ctx = tracing.ContextWithSpanFromContext(ctx, lbf.callCtx)
 
-	ref, err := lbf.getImmutableRef(ctx, req.Ref, req.Path)
+	ref, err := lbf.getImmutableRef(ctx, req.Ref)
 	if err != nil {
 		return nil, err
 	}
@@ -852,6 +852,16 @@ func (lbf *llbBridgeForwarder) StatFile(ctx context.Context, req *pb.StatFileReq
 	return &pb.StatFileResponse{Stat: st}, nil
 }
 
+func (lbf *llbBridgeForwarder) Evaluate(ctx context.Context, req *pb.EvaluateRequest) (*pb.EvaluateResponse, error) {
+	ctx = tracing.ContextWithSpanFromContext(ctx, lbf.callCtx)
+
+	_, err := lbf.getImmutableRef(ctx, req.Ref)
+	if err != nil {
+		return nil, err
+	}
+	return &pb.EvaluateResponse{}, nil
+}
+
 func (lbf *llbBridgeForwarder) Ping(context.Context, *pb.PingRequest) (*pb.PongResponse, error) {
 	workers := lbf.workers.WorkerInfos()
 	pbWorkers := make([]*apitypes.WorkerRecord, 0, len(workers))

frontend/gateway/grpcclient/client.go

@@ -387,30 +387,15 @@ func (c *grpcClient) Solve(ctx context.Context, creq client.SolveRequest) (res *
 		if c.caps.Supports(pb.CapGatewayEvaluateSolve) == nil {
 			req.Evaluate = creq.Evaluate
 		} else {
-			// If evaluate is not supported, fallback to running Stat(".") in order to
-			// trigger an evaluation of the result.
+			// If evaluate is not supported, fallback to running Stat(".") in
+			// order to trigger an evaluation of the result.
 			defer func() {
 				if res == nil {
 					return
 				}
-
-				var (
-					id  string
-					ref client.Reference
-				)
-				ref, err = res.SingleRef()
-				if err != nil {
-					for refID := range res.Refs {
-						id = refID
-						break
-					}
-				} else {
-					id = ref.(*reference).id
-				}
-
-				_, err = c.client.StatFile(ctx, &pb.StatFileRequest{
-					Ref:  id,
-					Path: ".",
+				err = res.EachRef(func(ref client.Reference) error {
+					_, err := ref.StatFile(ctx, client.StatRequest{Path: "."})
+					return err
 				})
 			}()
 		}
@@ -1054,6 +1039,15 @@ func (r *reference) ToState() (st llb.State, err error) {
 	return llb.NewState(defop), nil
 }
 
+func (r *reference) Evaluate(ctx context.Context) error {
+	req := &pb.EvaluateRequest{Ref: r.id}
+	_, err := r.c.client.Evaluate(ctx, req)
+	if err != nil {
+		return err
+	}
+	return nil
+}
+
 func (r *reference) ReadFile(ctx context.Context, req client.ReadRequest) ([]byte, error) {
 	rfr := &pb.ReadFileRequest{FilePath: req.Filename, Ref: r.id}
 	if r := req.Range; r != nil {

frontend/gateway/pb/caps.go

@@ -56,6 +56,8 @@ const (
 	// errors.
 	CapGatewayEvaluateSolve apicaps.CapID = "gateway.solve.evaluate"
 
+	CapGatewayEvaluate apicaps.CapID = "gateway.evaluate"
+
 	// CapGatewayWarnings is the capability to log warnings from frontend
 	CapGatewayWarnings apicaps.CapID = "gateway.warnings"
 
@@ -198,6 +200,13 @@ func init() {
 		Status:  apicaps.CapStatusExperimental,
 	})
 
+	Caps.Init(apicaps.Cap{
+		ID:      CapGatewayEvaluate,
+		Name:    "gateway evaluate",
+		Enabled: true,
+		Status:  apicaps.CapStatusExperimental,
+	})
+
 	Caps.Init(apicaps.Cap{
 		ID:      CapGatewayWarnings,
 		Name:    "logging warnings",