Implement Target support for ko builder

This implements support for the Target config field for the ko builder.
The Target field allows users to specify a target for `go build`. This
is necessary where the main package is not in the context directory.

Tracking: GoogleContainerTools#6041
Related: GoogleContainerTools#6054, GoogleContainerTools#6437

pkg/skaffold/build/ko/build.go

@@ -50,7 +50,7 @@ func (b *Builder) Build(ctx context.Context, out io.Writer, a *latestV1.Artifact
 	}
 	defer koPublisher.Close()
 
-	imageRef, err := b.buildAndPublish(ctx, a.ImageName, koBuilder, koPublisher)
+	imageRef, err := b.buildAndPublish(ctx, a, koBuilder, koPublisher)
 	if err != nil {
 		return "", fmt.Errorf("could not build and publish ko image %q: %w", a.ImageName, err)
 	}
@@ -60,10 +60,10 @@ func (b *Builder) Build(ctx context.Context, out io.Writer, a *latestV1.Artifact
 }
 
 // buildAndPublish the image using the ko builder and publisher.
-func (b *Builder) buildAndPublish(ctx context.Context, imageName string, koBuilder build.Interface, koPublisher publish.Interface) (name.Reference, error) {
-	importpath, err := getImportPath(imageName, koBuilder)
+func (b *Builder) buildAndPublish(ctx context.Context, a *latestV1.Artifact, koBuilder build.Interface, koPublisher publish.Interface) (name.Reference, error) {
+	importpath, err := getImportPath(a, koBuilder)
 	if err != nil {
-		return nil, fmt.Errorf("could not determine Go import path for ko image %q: %w", imageName, err)
+		return nil, fmt.Errorf("could not determine Go import path for ko image %q: %w", a.ImageName, err)
 	}
 	imageMap, err := b.publishImages(ctx, []string{importpath}, koPublisher, koBuilder)
 	if err != nil {
@@ -86,11 +86,16 @@ func (b *Builder) buildAndPublish(ctx context.Context, imageName string, koBuild
 //
 // If the image name does _not_ start with `ko://`, determine the Go import
 // path of the image workspace directory.
-func getImportPath(imageName string, koBuilder build.Interface) (string, error) {
-	if strings.HasPrefix(imageName, build.StrictScheme) {
-		return imageName, nil
+func getImportPath(a *latestV1.Artifact, koBuilder build.Interface) (string, error) {
+	if strings.HasPrefix(a.ImageName, build.StrictScheme) {
+		return a.ImageName, nil
 	}
-	return koBuilder.QualifyImport(".")
+	target := a.KoArtifact.Target
+	if target == "" {
+		// default to context directory
+		target = "."
+	}
+	return koBuilder.QualifyImport(target)
 }
 
 // getImageIdentifier returns the image tag or digest for published images (`pushImages=true`),

pkg/skaffold/build/ko/build_test.go

@@ -87,10 +87,12 @@ func Test_getImportPath(t *testing.T) {
 		expectedImportPath string
 	}{
 		{
-			description: "image name is ko-prefixed full Go import path",
+			description: "target is ignored when image name is ko-prefixed full Go import path",
 			artifact: &latestV1.Artifact{
 				ArtifactType: latestV1.ArtifactType{
-					KoArtifact: &latestV1.KoArtifact{},
+					KoArtifact: &latestV1.KoArtifact{
+						Target: "./target-should-be-ignored",
+					},
 				},
 				ImageName: "ko://git.example.com/org/foo",
 			},
@@ -113,9 +115,22 @@ func Test_getImportPath(t *testing.T) {
 					KoArtifact: &latestV1.KoArtifact{},
 				},
 				ImageName: "bar",
-				Workspace: "../docker",
+				Workspace: "./testdata/package-main-in-root",
+			},
+			expectedImportPath: "ko://github.com/GoogleContainerTools/skaffold/pkg/skaffold/build/ko/testdata/package-main-in-root",
+		},
+		{
+			description: "plain image name with workspace directory and target",
+			artifact: &latestV1.Artifact{
+				ArtifactType: latestV1.ArtifactType{
+					KoArtifact: &latestV1.KoArtifact{
+						Target: "./baz",
+					},
+				},
+				ImageName: "baz-image",
+				Workspace: "./testdata/package-main-not-in-root",
 			},
-			expectedImportPath: "ko://github.com/GoogleContainerTools/skaffold/pkg/skaffold/build/docker", // this package + "../docker"
+			expectedImportPath: "ko://github.com/GoogleContainerTools/skaffold/pkg/skaffold/build/ko/testdata/package-main-not-in-root/baz",
 		},
 	}
 	for _, test := range tests {
@@ -124,7 +139,7 @@ func Test_getImportPath(t *testing.T) {
 			koBuilder, err := b.newKoBuilder(context.Background(), test.artifact)
 			t.CheckNoError(err)
 
-			gotImportPath, err := getImportPath(test.artifact.ImageName, koBuilder)
+			gotImportPath, err := getImportPath(test.artifact, koBuilder)
 			t.CheckNoError(err)
 
 			t.CheckDeepEqual(test.expectedImportPath, gotImportPath)

pkg/skaffold/build/ko/schema/temporary.go

@@ -36,6 +36,14 @@ type KoArtifact struct {
 	// Defaults to `all` to build for all platforms supported by the
 	// base image.
 	Platforms []string `yaml:"platforms,omitempty"`
+
+	// Target is the location of the main package.
+	// If target is specified as a relative path, it is relative to the `context` directory.
+	// If target is empty, the ko builder looks for the main package in the `context` directory only, but not in any subdirectories.
+	// If target is a pattern with wildcards, such as `./...`, the expansion must contain only one main package, otherwise ko fails.
+	// Target is ignored if the `ImageName` starts with `ko://`.
+	// Example: `./cmd/foo`
+	Target string `yaml:"target,omitempty"`
 }
 
 // KoDependencies is used to specify dependencies for an artifact built by ko.

pkg/skaffold/build/ko/testdata/package-main-in-root/go.mod

@@ -0,0 +1,3 @@
+module github.com/GoogleContainerTools/skaffold/pkg/skaffold/build/ko/testdata/package-main-in-root
+
+go 1.13

pkg/skaffold/build/ko/testdata/package-main-in-root/main.go

@@ -0,0 +1,14 @@
+package main
+
+import (
+	"fmt"
+	"time"
+)
+
+func main() {
+	for {
+		fmt.Println("Hello world!")
+
+		time.Sleep(time.Second * 1)
+	}
+}

pkg/skaffold/build/ko/testdata/package-main-not-in-root/baz/main.go

@@ -0,0 +1,14 @@
+package main
+
+import (
+	"fmt"
+	"time"
+)
+
+func main() {
+	for {
+		fmt.Println("Hello world!")
+
+		time.Sleep(time.Second * 1)
+	}
+}

pkg/skaffold/build/ko/testdata/package-main-not-in-root/go.mod

@@ -0,0 +1,3 @@
+module github.com/GoogleContainerTools/skaffold/pkg/skaffold/build/ko/testdata/package-main-not-in-root
+
+go 1.13