Add custom_build(outputs_image_ref_to=...) Tiltfile API (#3769)

internal/tiltfile/docker.go

@@ -55,9 +55,12 @@ type dockerImage struct {
 	// Whether this has been matched up yet to a deploy resource.
 	matched bool
 
-	dependencyIDs    []model.TargetID
-	disablePush      bool
-	skipsLocalDocker bool
+	dependencyIDs []model.TargetID
+
+	// Only applicable to custom_build
+	disablePush       bool
+	skipsLocalDocker  bool
+	outputsImageRefTo string
 
 	liveUpdate model.LiveUpdate
 }
@@ -271,6 +274,7 @@ func (s *tiltfileState) customBuild(thread *starlark.Thread, fn *starlark.Builti
 	var entrypoint starlark.Value
 	var containerArgsVal starlark.Sequence
 	var skipsLocalDocker bool
+	outputsImageRefTo := value.NewLocalPathUnpacker(thread)
 
 	err := s.unpackArgs(fn.Name(), args, kwargs,
 		"ref", &dockerRef,
@@ -285,6 +289,7 @@ func (s *tiltfileState) customBuild(thread *starlark.Thread, fn *starlark.Builti
 		"entrypoint?", &entrypoint,
 		"container_args?", &containerArgsVal,
 		"command_bat_val", &commandBatVal,
+		"outputs_image_ref_to", &outputsImageRefTo,
 	)
 	if err != nil {
 		return nil, err
@@ -342,19 +347,24 @@ func (s *tiltfileState) customBuild(thread *starlark.Thread, fn *starlark.Builti
 		return nil, fmt.Errorf("Argument 2 (command) can't be empty")
 	}
 
+	if tag != "" && outputsImageRefTo.Value != "" {
+		return nil, fmt.Errorf("Cannot specify both tag= and outputs_image_ref_to=")
+	}
+
 	img := &dockerImage{
-		workDir:          starkit.AbsWorkingDir(thread),
-		configurationRef: container.NewRefSelector(ref),
-		customCommand:    command,
-		customDeps:       localDeps,
-		customTag:        tag,
-		disablePush:      disablePush,
-		skipsLocalDocker: skipsLocalDocker,
-		liveUpdate:       liveUpdate,
-		matchInEnvVars:   matchInEnvVars,
-		ignores:          ignores,
-		entrypoint:       entrypointCmd,
-		containerArgs:    containerArgs,
+		workDir:           starkit.AbsWorkingDir(thread),
+		configurationRef:  container.NewRefSelector(ref),
+		customCommand:     command,
+		customDeps:        localDeps,
+		customTag:         tag,
+		disablePush:       disablePush,
+		skipsLocalDocker:  skipsLocalDocker,
+		liveUpdate:        liveUpdate,
+		matchInEnvVars:    matchInEnvVars,
+		ignores:           ignores,
+		entrypoint:        entrypointCmd,
+		containerArgs:     containerArgs,
+		outputsImageRefTo: outputsImageRefTo.Value,
 	}
 
 	err = s.buildIndex.addImage(img)

internal/tiltfile/docker_test.go

@@ -102,3 +102,40 @@ custom_build('gcr.io/fe', 'docker build -t $EXPECTED_REF .', ['src'])
 
 	assert.Contains(t, localPathStrings, f.JoinPath("src"))
 }
+
+func TestCustomBuildOutputsImageRefsTo(t *testing.T) {
+	f := newFixture(t)
+	defer f.TearDown()
+
+	f.yaml("fe.yaml", deployment("fe", image("gcr.io/fe")))
+	f.file("Dockerfile", `
+FROM alpine
+ADD . .
+`)
+	f.file("Tiltfile", `
+k8s_yaml('fe.yaml')
+custom_build('gcr.io/fe', 'export MY_REF="gcr.io/fe:dev" && docker build -t $MY_REF . && echo $MY_REF > ref.txt',
+            ['src'],
+            outputs_image_ref_to='ref.txt')
+`)
+
+	f.load()
+
+	m := f.assertNextManifest("fe")
+	it := m.ImageTargets[0]
+	assert.Equal(t, f.JoinPath("ref.txt"), it.CustomBuildInfo().OutputsImageRefTo)
+}
+
+func TestCustomBuildOutputsImageRefsToIncompatibleWithTag(t *testing.T) {
+	f := newFixture(t)
+	defer f.TearDown()
+
+	f.file("Tiltfile", `
+custom_build('gcr.io/fe', 'export MY_REF="gcr.io/fe:dev" && docker build -t $MY_REF . && echo $MY_REF > ref.txt',
+            ['src'],
+            tag='dev',
+            outputs_image_ref_to='ref.txt')
+`)
+
+	f.loadErrString("Cannot specify both tag= and outputs_image_ref_to=")
+}

internal/tiltfile/tiltfile_state.go

@@ -1398,13 +1398,14 @@ func (s *tiltfileState) imgTargetsForDependencyIDsHelper(ids []model.TargetID, c
 			})
 		case CustomBuild:
 			r := model.CustomBuild{
-				WorkDir:          image.workDir,
-				Command:          image.customCommand,
-				Deps:             image.customDeps,
-				Tag:              image.customTag,
-				DisablePush:      image.disablePush,
-				SkipsLocalDocker: image.skipsLocalDocker,
-				LiveUpdate:       lu,
+				WorkDir:           image.workDir,
+				Command:           image.customCommand,
+				Deps:              image.customDeps,
+				Tag:               image.customTag,
+				DisablePush:       image.disablePush,
+				SkipsLocalDocker:  image.skipsLocalDocker,
+				OutputsImageRefTo: image.outputsImageRefTo,
+				LiveUpdate:        lu,
 			}
 			iTarget = iTarget.WithBuildDetails(r).
 				MaybeIgnoreRegistry()

internal/tiltfile/value/path.go

@@ -0,0 +1,26 @@
+package value
+
+import (
+	"go.starlark.net/starlark"
+)
+
+type LocalPath struct {
+	t     *starlark.Thread
+	Value string
+}
+
+func NewLocalPathUnpacker(t *starlark.Thread) LocalPath {
+	return LocalPath{
+		t: t,
+	}
+}
+
+func (p *LocalPath) Unpack(v starlark.Value) error {
+	str, err := ValueToAbsPath(p.t, v)
+	if err != nil {
+		return err
+	}
+
+	p.Value = str
+	return nil
+}

internal/tiltfile/value/value.go

@@ -37,7 +37,7 @@ func ValueToAbsPath(thread *starlark.Thread, v starlark.Value) (string, error) {
 		return pathMaker.MakeLocalPath("."), nil
 	}
 
-	str, ok := v.(starlark.String)
+	str, ok := starlark.AsString(v)
 	if ok {
 		return starkit.AbsPath(thread, string(str)), nil
 	}