Allow caching from built artifact on local Docker build

docs/content/en/docs/pipeline-stages/builders/docker.md

@@ -33,6 +33,10 @@ of `skaffold.yaml`. The following options can optionally be configured:
 
 {{< schema root="LocalBuild" >}}
 
+The `docker` builder replaces cache references to the
+artifact image with the tagged image to allow caching from the
+previously built image.
+
 **Example**
 
 The following `build` section instructs Skaffold to build a

docs/content/en/samples/builders/local.yaml

@@ -1,4 +1,9 @@
 build:
   artifacts:
   - image: gcr.io/k8s-skaffold/example
+    docker:
+      cacheFrom:
+      # Local Docker builder replaces cache references to the artifact image with
+      # the tagged image reference, useful for caching from the previous build.
+      - gcr.io/k8s-skaffold/example
   local: {}

pkg/skaffold/build/docker/docker.go

@@ -28,10 +28,12 @@ import (
 	"github.com/GoogleContainerTools/skaffold/pkg/skaffold/output"
 	latestV1 "github.com/GoogleContainerTools/skaffold/pkg/skaffold/schema/latest/v1"
 	"github.com/GoogleContainerTools/skaffold/pkg/skaffold/util"
+	"github.com/GoogleContainerTools/skaffold/pkg/skaffold/util/stringslice"
 	"github.com/GoogleContainerTools/skaffold/pkg/skaffold/warnings"
 )
 
 func (b *Builder) Build(ctx context.Context, out io.Writer, a *latestV1.Artifact, tag string) (string, error) {
+	a = adjustCacheFrom(a, tag)
 	instrumentation.AddAttributesToCurrentSpanFromContext(ctx, map[string]string{
 		"BuildType":   "docker",
 		"Context":     instrumentation.PII(a.Workspace),
@@ -132,3 +134,27 @@ func (b *Builder) pullCacheFromImages(ctx context.Context, out io.Writer, a *lat
 
 	return nil
 }
+
+// adjustCacheFrom returns an artifact where any cache references from the artifactImage is changed to the tagged built image name instead.
+func adjustCacheFrom(a *latestV1.Artifact, artifactTag string) *latestV1.Artifact {
+	if os.Getenv("SKAFFOLD_DISABLE_DOCKER_CACHE_ADJUSTMENT") != "" {
+		// allow this behaviour to be disabled
+		return a
+	}
+
+	if !stringslice.Contains(a.DockerArtifact.CacheFrom, a.ImageName) {
+		return a
+	}
+
+	cf := make([]string, 0, len(a.DockerArtifact.CacheFrom))
+	for _, image := range a.DockerArtifact.CacheFrom {
+		if image == a.ImageName {
+			cf = append(cf, artifactTag)
+		} else {
+			cf = append(cf, image)
+		}
+	}
+	copy := *a
+	copy.DockerArtifact.CacheFrom = cf
+	return &copy
+}

pkg/skaffold/build/docker/docker_test.go

@@ -21,6 +21,7 @@ import (
 	"fmt"
 	"io/ioutil"
 	"path/filepath"
+	"strings"
 	"testing"
 
 	"github.com/docker/docker/api/types"
@@ -178,6 +179,64 @@ func TestDockerCLIBuild(t *testing.T) {
 	}
 }
 
+func TestDockerCLICheckCacheFromArgs(t *testing.T) {
+	tests := []struct {
+		description       string
+		artifact          *latestV1.Artifact
+		tag               string
+		expectedCacheFrom []string
+	}{
+		{
+			description: "multiple cache-from images",
+			artifact: &latestV1.Artifact{
+				ImageName: "gcr.io/k8s-skaffold/test",
+				ArtifactType: latestV1.ArtifactType{
+					DockerArtifact: &latestV1.DockerArtifact{
+						CacheFrom: []string{"from/image1", "from/image2"},
+					},
+				},
+			},
+			tag:               "tag",
+			expectedCacheFrom: []string{"from/image1", "from/image2"},
+		},
+		{
+			description: "cache-from self uses tagged image",
+			artifact: &latestV1.Artifact{
+				ImageName: "gcr.io/k8s-skaffold/test",
+				ArtifactType: latestV1.ArtifactType{
+					DockerArtifact: &latestV1.DockerArtifact{
+						CacheFrom: []string{"gcr.io/k8s-skaffold/test"},
+					},
+				},
+			},
+			tag:               "gcr.io/k8s-skaffold/test:tagged",
+			expectedCacheFrom: []string{"gcr.io/k8s-skaffold/test:tagged"},
+		},
+	}
+
+	for _, test := range tests {
+		testutil.Run(t, test.description, func(t *testutil.T) {
+			t.NewTempDir().Touch("Dockerfile").Chdir()
+			dockerfilePath, _ := filepath.Abs("Dockerfile")
+			a := *test.artifact
+			a.Workspace = "."
+			a.DockerArtifact.DockerfilePath = dockerfilePath
+			t.Override(&docker.EvalBuildArgs, func(_ config.RunMode, _ string, _ string, args map[string]*string, _ map[string]*string) (map[string]*string, error) {
+				return args, nil
+			})
+
+			mockCmd := testutil.CmdRun(
+				"docker build . --file " + dockerfilePath + " -t " + test.tag + " --cache-from " + strings.Join(test.expectedCacheFrom, " --cache-from "),
+			)
+			t.Override(&util.DefaultExecCommand, mockCmd)
+
+			builder := NewArtifactBuilder(fakeLocalDaemonWithExtraEnv([]string{}), mockConfig{}, true, util.BoolPtr(false), false, mockArtifactResolver{make(map[string]string)}, nil)
+			_, err := builder.Build(context.Background(), ioutil.Discard, &a, test.tag)
+			t.CheckNoError(err)
+		})
+	}
+}
+
 func fakeLocalDaemonWithExtraEnv(extraEnv []string) docker.LocalDaemon {
 	return docker.NewLocalDaemon(&testutil.FakeAPIClient{}, extraEnv, false, nil)
 }