Add support for custom platform

.drone.yml

@@ -4,7 +4,7 @@ name: default
 
 steps:
 - name: build
-  image: golang
+  image: golang:1.17.2
   commands:
   - go test ./...
   - sh scripts/build.sh

README.md

@@ -51,3 +51,35 @@ docker run --rm \
     -w /drone \
     plugins/kaniko:linux-amd64
 ```
+
+### Automatic Tagging
+
+With auto tagging enabled, semantic versions can be passed to PLUGIN_TAGS directly for expansion:
+
+```console
+docker run --rm \
+    -e PLUGIN_TAGS=v1.2.3,latest \
+    -e PLUGIN_AUTO_TAG=true \
+    -v $(pwd):/drone \
+    -w /drone \
+    plugins/kaniko:linux-amd64
+```
+would both be equivalent to
+
+```
+PLUGIN_TAGS=1,1.2,1.2.3,latest
+```
+
+This allows for passing `$DRONE_TAG` directly as a tag for repos that use [semver](https://semver.org) tags.
+
+To avoid confusion between repo tags and image tags, `PLUGIN_AUTO_TAG` also recognizes a semantic version
+without the `v` prefix.  As such, the following is also equivalent to the above:
+
+```console
+docker run --rm \
+    -e PLUGIN_TAGS=1.2.3,latest \
+    -e PLUGIN_AUTO_TAG=true \
+    -v $(pwd):/drone \
+    -w /drone \
+    plugins/kaniko:linux-amd64
+```

cmd/kaniko-docker/main.go

@@ -12,7 +12,7 @@ import (
 	"github.com/urfave/cli"
 
 	kaniko "github.com/drone/drone-kaniko"
-	"github.com/drone/drone-kaniko/cmd/artifact"
+	"github.com/drone/drone-kaniko/pkg/artifact"
 )
 
 const (
@@ -20,8 +20,9 @@ const (
 	dockerPath       string = "/kaniko/.docker"
 	dockerConfigPath string = "/kaniko/.docker/config.json"
 
-	v1Registry string = "https://index.docker.io/v1/" // Default registry
+	v1RegistryURL    string = "https://index.docker.io/v1/" // Default registry
-	v2Registry string = "https://index.docker.io/v2/" // v2 registry is not supported
+	v2RegistryURL    string = "https://index.docker.io/v2/" // v2 registry is not supported
+	v2HubRegistryURL string = "https://registry.hub.docker.com/v2/"
 
 	defaultDigestFile string = "/kaniko/digest-file"
 )
@@ -63,6 +64,11 @@ func main() {
 			EnvVar:   "PLUGIN_TAGS",
 			FilePath: ".tags",
 		},
+		cli.BoolFlag{
+			Name:   "auto_tag",
+			Usage:  "enable for semver tagging",
+			EnvVar: "PLUGIN_AUTO_TAG",
+		},
 		cli.StringSliceFlag{
 			Name:   "args",
 			Usage:  "build args",
@@ -86,7 +92,7 @@ func main() {
 		cli.StringFlag{
 			Name:   "registry",
 			Usage:  "docker registry",
-			Value:  v1Registry,
+			Value:  v1RegistryURL,
 			EnvVar: "PLUGIN_REGISTRY",
 		},
 		cli.StringFlag{
@@ -139,6 +145,11 @@ func main() {
 			Usage:  "Set this flag with value as oneof <panic|fatal|error|warn|info|debug|trace> to set the logging level for kaniko. Defaults to info.",
 			EnvVar: "PLUGIN_VERBOSITY",
 		},
+		cli.StringFlag{
+			Name:   "platform",
+			Usage:  "Allows to build with another default platform than the host, similarly to docker build --platform",
+			EnvVar: "PLUGIN_PLATFORM",
+		},
 	}
 
 	if err := app.Run(os.Args); err != nil {
@@ -162,6 +173,7 @@ func run(c *cli.Context) error {
 			Dockerfile:    c.String("dockerfile"),
 			Context:       c.String("context"),
 			Tags:          c.StringSlice("tags"),
+			AutoTag:       c.Bool("auto_tag"),
 			Args:          c.StringSlice("args"),
 			Target:        c.String("target"),
 			Repo:          c.String("repo"),
@@ -174,6 +186,7 @@ func run(c *cli.Context) error {
 			DigestFile:    defaultDigestFile,
 			NoPush:        noPush,
 			Verbosity:     c.String("verbosity"),
+			Platform:      c.String("platform"),
 		},
 		Artifact: kaniko.Artifact{
 			Tags:         c.StringSlice("tags"),
@@ -198,10 +211,10 @@ func createDockerCfgFile(username, password, registry string) error {
 		return fmt.Errorf("Registry must be specified")
 	}
 
-	if registry == v2Registry {
+	if registry == v2RegistryURL || registry == v2HubRegistryURL {
 		fmt.Println("Docker v2 registry is not supported in kaniko. Refer issue: https://github.com/GoogleContainerTools/kaniko/issues/1209")
-		fmt.Printf("Using v1 registry instead: %s\n", v1Registry)
+		fmt.Printf("Using v1 registry instead: %s\n", v1RegistryURL)
-		registry = v1Registry
+		registry = v1RegistryURL
 	}
 
 	err := os.MkdirAll(dockerPath, 0600)

cmd/kaniko-ecr/main.go

@@ -14,7 +14,7 @@ import (
 	"github.com/aws/aws-sdk-go-v2/service/ecrpublic"
 	"github.com/aws/smithy-go"
 	kaniko "github.com/drone/drone-kaniko"
-	"github.com/drone/drone-kaniko/cmd/artifact"
+	"github.com/drone/drone-kaniko/pkg/artifact"
 	"github.com/drone/drone-kaniko/pkg/docker"
 	"github.com/joho/godotenv"
 	"github.com/pkg/errors"
@@ -78,6 +78,11 @@ func main() {
 			EnvVar:   "PLUGIN_TAGS",
 			FilePath: ".tags",
 		},
+		cli.BoolFlag{
+			Name:   "auto_tag",
+			Usage:  "enable for semver tagging",
+			EnvVar: "PLUGIN_AUTO_TAG",
+		},
 		cli.StringSliceFlag{
 			Name:   "args",
 			Usage:  "build args",
@@ -169,6 +174,11 @@ func main() {
 			Usage:  "Set this flag with value as oneof <panic|fatal|error|warn|info|debug|trace> to set the logging level for kaniko. Defaults to info.",
 			EnvVar: "PLUGIN_VERBOSITY",
 		},
+		cli.StringFlag{
+			Name:   "platform",
+			Usage:  "Allows to build with another default platform than the host, similarly to docker build --platform",
+			EnvVar: "PLUGIN_PLATFORM",
+		},
 	}
 
 	if err := app.Run(os.Args); err != nil {
@@ -235,6 +245,7 @@ func run(c *cli.Context) error {
 			Dockerfile:   c.String("dockerfile"),
 			Context:      c.String("context"),
 			Tags:         c.StringSlice("tags"),
+			AutoTag:      c.Bool("auto_tag"),
 			Args:         c.StringSlice("args"),
 			Target:       c.String("target"),
 			Repo:         fmt.Sprintf("%s/%s", c.String("registry"), c.String("repo")),
@@ -246,6 +257,7 @@ func run(c *cli.Context) error {
 			DigestFile:   defaultDigestFile,
 			NoPush:       noPush,
 			Verbosity:    c.String("verbosity"),
+			Platform:     c.String("platform"),
 		},
 		Artifact: kaniko.Artifact{
 			Tags:         c.StringSlice("tags"),

cmd/kaniko-gcr/main.go

@@ -11,7 +11,7 @@ import (
 	"github.com/urfave/cli"
 
 	kaniko "github.com/drone/drone-kaniko"
-	"github.com/drone/drone-kaniko/cmd/artifact"
+	"github.com/drone/drone-kaniko/pkg/artifact"
 )
 
 const (
@@ -59,6 +59,11 @@ func main() {
 			EnvVar:   "PLUGIN_TAGS",
 			FilePath: ".tags",
 		},
+		cli.BoolFlag{
+			Name:   "auto_tag",
+			Usage:  "enable for semver tagging",
+			EnvVar: "PLUGIN_AUTO_TAG",
+		},
 		cli.StringSliceFlag{
 			Name:   "args",
 			Usage:  "build args",
@@ -125,6 +130,11 @@ func main() {
 			Usage:  "Set this flag as --verbosity=<panic|fatal|error|warn|info|debug|trace> to set the logging level for kaniko. Defaults to info.",
 			EnvVar: "PLUGIN_VERBOSITY",
 		},
+		cli.StringFlag{
+			Name:   "platform",
+			Usage:  "Allows to build with another default platform than the host, similarly to docker build --platform",
+			EnvVar: "PLUGIN_PLATFORM",
+		},
 	}
 
 	if err := app.Run(os.Args); err != nil {
@@ -136,8 +146,10 @@ func run(c *cli.Context) error {
 	noPush := c.Bool("no-push")
 	jsonKey := c.String("json-key")
 
-	// only setup auth when pushing or credentials are defined
+	// JSON key may not be set in the following cases:
-	if !noPush || jsonKey != "" {
+	// 1. Image does not need to be pushed to GCR.
+	// 2. Workload identity is set on GKE in which pod will inherit the credentials via service account.
+	if jsonKey != "" {
 		if err := setupGCRAuth(jsonKey); err != nil {
 			return err
 		}
@@ -148,6 +160,7 @@ func run(c *cli.Context) error {
 			Dockerfile:   c.String("dockerfile"),
 			Context:      c.String("context"),
 			Tags:         c.StringSlice("tags"),
+			AutoTag:      c.Bool("auto_tag"),
 			Args:         c.StringSlice("args"),
 			Target:       c.String("target"),
 			Repo:         fmt.Sprintf("%s/%s", c.String("registry"), c.String("repo")),
@@ -159,6 +172,7 @@ func run(c *cli.Context) error {
 			DigestFile:   defaultDigestFile,
 			NoPush:       noPush,
 			Verbosity:    c.String("verbosity"),
+			Platform:     c.String("platform"),
 		},
 		Artifact: kaniko.Artifact{
 			Tags:         c.StringSlice("tags"),
@@ -172,10 +186,6 @@ func run(c *cli.Context) error {
 }
 
 func setupGCRAuth(jsonKey string) error {
-	if jsonKey == "" {
-		return fmt.Errorf("GCR JSON key must be specified")
-	}
-
 	err := ioutil.WriteFile(gcrKeyPath, []byte(jsonKey), 0644)
 	if err != nil {
 		return errors.Wrap(err, "failed to write GCR JSON key")

docker/docker/Dockerfile.linux.amd64

@@ -1,4 +1,4 @@
-FROM gcr.io/kaniko-project/executor:v1.5.2
+FROM gcr.io/kaniko-project/executor:v1.6.0
 
 ADD release/linux/amd64/kaniko-docker /kaniko/
 ENTRYPOINT ["/kaniko/kaniko-docker"]

docker/docker/Dockerfile.linux.arm64

@@ -1,4 +1,4 @@
-FROM gcr.io/kaniko-project/executor:arm64-v1.5.2
+FROM gcr.io/kaniko-project/executor:arm64-v1.6.0
 
 ENV HOME /root
 ENV USER root

docker/ecr/Dockerfile.linux.amd64

@@ -1,4 +1,4 @@
-FROM gcr.io/kaniko-project/executor:v1.5.2
+FROM gcr.io/kaniko-project/executor:v1.6.0
 
 ADD release/linux/amd64/kaniko-ecr /kaniko/
 ENTRYPOINT ["/kaniko/kaniko-ecr"]

docker/ecr/Dockerfile.linux.arm64

@@ -1,4 +1,4 @@
-FROM gcr.io/kaniko-project/executor:arm64-v1.5.2
+FROM gcr.io/kaniko-project/executor:arm64-v1.6.0
 
 ENV HOME /root
 ENV USER root

docker/gcr/Dockerfile.linux.amd64

@@ -1,4 +1,4 @@
-FROM gcr.io/kaniko-project/executor:v1.5.2
+FROM gcr.io/kaniko-project/executor:v1.6.0
 
 ADD release/linux/amd64/kaniko-gcr /kaniko/
 ENTRYPOINT ["/kaniko/kaniko-gcr"]

docker/gcr/Dockerfile.linux.arm64

@@ -1,4 +1,4 @@
-FROM gcr.io/kaniko-project/executor:arm64-v1.5.2
+FROM gcr.io/kaniko-project/executor:arm64-v1.6.0
 
 ENV HOME /root
 ENV USER root

go.mod

@@ -6,10 +6,28 @@ require (
 	github.com/aws/aws-sdk-go-v2/service/ecr v1.4.3
 	github.com/aws/aws-sdk-go-v2/service/ecrpublic v1.4.3
 	github.com/aws/smithy-go v1.7.0
+	github.com/google/go-cmp v0.5.6
 	github.com/joho/godotenv v1.3.0
 	github.com/pkg/errors v0.9.1
 	github.com/sirupsen/logrus v1.3.0
 	github.com/urfave/cli v1.22.2
+	golang.org/x/mod v0.4.2
 )
 
-go 1.13
+require (
+	github.com/aws/aws-sdk-go-v2/credentials v1.3.3 // indirect
+	github.com/aws/aws-sdk-go-v2/feature/ec2/imds v1.4.1 // indirect
+	github.com/aws/aws-sdk-go-v2/internal/ini v1.2.1 // indirect
+	github.com/aws/aws-sdk-go-v2/service/internal/presigned-url v1.2.3 // indirect
+	github.com/aws/aws-sdk-go-v2/service/sso v1.3.3 // indirect
+	github.com/aws/aws-sdk-go-v2/service/sts v1.6.2 // indirect
+	github.com/cpuguy83/go-md2man/v2 v2.0.0-20190314233015-f79a8a8ca69d // indirect
+	github.com/jmespath/go-jmespath v0.4.0 // indirect
+	github.com/konsorten/go-windows-terminal-sequences v1.0.1 // indirect
+	github.com/russross/blackfriday/v2 v2.0.1 // indirect
+	github.com/shurcooL/sanitized_anchor_name v1.0.0 // indirect
+	golang.org/x/crypto v0.0.0-20191011191535-87dc89f01550 // indirect
+	golang.org/x/sys v0.0.0-20190412213103-97732733099d // indirect
+)
+
+go 1.17

go.sum

@@ -53,13 +53,25 @@ github.com/stretchr/testify v1.2.2 h1:bSDNvY7ZPG5RlJ8otE/7V6gMiyenm9RtJ7IUVIAoJ1
 github.com/stretchr/testify v1.2.2/go.mod h1:a8OnRcib4nhh0OaRAV+Yts87kKdq0PP7pXfy6kDkUVs=
 github.com/urfave/cli v1.22.2 h1:gsqYFH8bb9ekPA12kRo0hfjngWQjkJPlN9R0N78BoUo=
 github.com/urfave/cli v1.22.2/go.mod h1:Gos4lmkARVdJ6EkW0WaNv/tZAAMe9V7XWyB60NtXRu0=
-golang.org/x/crypto v0.0.0-20180904163835-0709b304e793 h1:u+LnwYTOOW7Ukr/fppxEb1Nwz0AtPflrblfvUudpo+I=
 golang.org/x/crypto v0.0.0-20180904163835-0709b304e793/go.mod h1:6SG95UA2DQfeDnfUPMdvaQW0Q7yPrPDi9nlGo2tz2b4=
-golang.org/x/sys v0.0.0-20180905080454-ebe1bf3edb33 h1:I6FyU15t786LL7oL/hn43zqTuEGr4PN7F4XJ1p4E3Y8=
+golang.org/x/crypto v0.0.0-20190308221718-c2843e01d9a2/go.mod h1:djNgcEr1/C05ACkg1iLfiJU5Ep61QUkGW8qpdssI0+w=
+golang.org/x/crypto v0.0.0-20191011191535-87dc89f01550 h1:ObdrDkeb4kJdCP557AjRjq69pTHfNouLtWZG7j9rPN8=
+golang.org/x/crypto v0.0.0-20191011191535-87dc89f01550/go.mod h1:yigFU9vqHzYiE8UmvKecakEJjdnWj3jj499lnFckfCI=
+golang.org/x/mod v0.4.2 h1:Gz96sIWK3OalVv/I/qNygP42zyoKp3xptRVCWRFEBvo=
+golang.org/x/mod v0.4.2/go.mod h1:s0Qsj1ACt9ePp/hMypM3fl4fZqREWJwdYDEqhRiZZUA=
+golang.org/x/net v0.0.0-20190404232315-eb5bcb51f2a3/go.mod h1:t9HGtf8HONx5eT2rtn7q6eTqICYqUVnKs3thJo3Qplg=
+golang.org/x/net v0.0.0-20190620200207-3b0461eec859/go.mod h1:z5CRVTTTmAJ677TzLLGU+0bjPO0LkuOLi4/5GtJWs/s=
+golang.org/x/sync v0.0.0-20190423024810-112230192c58/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
 golang.org/x/sys v0.0.0-20180905080454-ebe1bf3edb33/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
+golang.org/x/sys v0.0.0-20190215142949-d0b11bdaac8a/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
+golang.org/x/sys v0.0.0-20190412213103-97732733099d h1:+R4KGOnez64A81RvjARKc4UT5/tI9ujCIVX+P5KiHuI=
+golang.org/x/sys v0.0.0-20190412213103-97732733099d/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
+golang.org/x/text v0.3.0/go.mod h1:NqM8EUOU14njkJ3fqMW+pc6Ldnwhi/IjpwHt7yyuwOQ=
+golang.org/x/tools v0.0.0-20191119224855-298f0cb1881e/go.mod h1:b+2E5dAYhXwXZwtnZ6UAqBI28+e2cm9otk0dWdXHAEo=
+golang.org/x/xerrors v0.0.0-20190717185122-a985d3407aa7/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=
+golang.org/x/xerrors v0.0.0-20191011141410-1b5146add898/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=
 golang.org/x/xerrors v0.0.0-20191204190536-9bdfabe68543 h1:E7g+9GITq07hpfrRu66IVDexMakfv52eLZ2CXBWiKr4=
 golang.org/x/xerrors v0.0.0-20191204190536-9bdfabe68543/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=
-gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405 h1:yhCVgyC4o1eVCa2tZl7eS0r+SDo693bJlVdllGtEeKM=
 gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
 gopkg.in/yaml.v2 v2.2.2/go.mod h1:hI93XBmqTisBFMUTm0b8Fm+jr3Dg1NNxqwp+5A1VGuI=
 gopkg.in/yaml.v2 v2.2.8 h1:obN1ZagJSUGI0Ek/LBmuj4SNLPfIny3KsKFopxRdj10=

kaniko.go

@@ -7,7 +7,8 @@ import (
 	"os/exec"
 	"strings"
 
-	"github.com/drone/drone-kaniko/cmd/artifact"
+	"github.com/drone/drone-kaniko/pkg/artifact"
+	"golang.org/x/mod/semver"
 )
 
 type (
@@ -16,6 +17,7 @@ type (
 		Dockerfile    string   // Docker build Dockerfile
 		Context       string   // Docker build context
 		Tags          []string // Docker build tags
+		AutoTag       bool     // Set this to create semver-tagged labels
 		Args          []string // Docker build args
 		Target        string   // Docker build target
 		Repo          string   // Docker build repository
@@ -28,7 +30,9 @@ type (
 		DigestFile    string   // Digest file location
 		NoPush        bool     // Set this flag if you only want to build the image, without pushing to a registry
 		Verbosity     string   // Log level
+		Platform      string   // Allows to build with another default platform than the host, similarly to docker build --platform
 	}
+
 	// Artifact defines content of artifact file
 	Artifact struct {
 		Tags         []string                  // Docker artifact tags
@@ -45,6 +49,47 @@ type (
 	}
 )
 
+// labelsForTag returns the labels to use for the given tag, subject to the value of AutoTag.
+//
+// Build information (e.g. +linux_amd64) is carried through to all labels.
+// Pre-release information (e.g. -rc1) suppresses major and major+minor auto-labels.
+func (b Build) labelsForTag(tag string) (labels []string) {
+	// We strip "v" off of the beginning of semantic versions, as they are not used in docker tags
+	const VersionPrefix = "v"
+
+	// Semantic Versions don't allow underscores, so replace them with dashes.
+	//   https://semver.org/
+	semverTag := strings.ReplaceAll(tag, "_", "-")
+
+	// Allow tags of the form "1.2.3" as well as "v1.2.3" to avoid confusion.
+	if withV := VersionPrefix + semverTag; !semver.IsValid(semverTag) && semver.IsValid(withV) {
+		semverTag = withV
+	}
+
+	// Pass through tags if auto-tag is not set, or if the tag is not a semantic version
+	if !b.AutoTag || !semver.IsValid(semverTag) {
+		return []string{tag}
+	}
+	tag = semverTag
+
+	// If the version is pre-release, only the full release should be tagged, not the major/minor versions.
+	if semver.Prerelease(tag) != "" {
+		return []string{
+			strings.TrimPrefix(tag, VersionPrefix),
+		}
+	}
+
+	// tagFor carries any build information from the semantic version through to major and minor tags.
+	labelFor := func(base string) string {
+		return strings.TrimPrefix(base, VersionPrefix) + semver.Build(tag)
+	}
+	return []string{
+		labelFor(semver.Major(tag)),
+		labelFor(semver.MajorMinor(tag)),
+		labelFor(semver.Canonical(tag)),
+	}
+}
+
 // Exec executes the plugin step
 func (p Plugin) Exec() error {
 	if !p.Build.NoPush && p.Build.Repo == "" {
@@ -63,7 +108,9 @@ func (p Plugin) Exec() error {
 	// Set the destination repository
 	if !p.Build.NoPush {
 		for _, tag := range p.Build.Tags {
-			cmdArgs = append(cmdArgs, fmt.Sprintf("--destination=%s:%s", p.Build.Repo, tag))
+			for _, label := range p.Build.labelsForTag(tag) {
+				cmdArgs = append(cmdArgs, fmt.Sprintf("--destination=%s:%s", p.Build.Repo, label))
+			}
 		}
 	}
 	// Set the build arguments
@@ -111,6 +158,10 @@ func (p Plugin) Exec() error {
 		cmdArgs = append(cmdArgs, fmt.Sprintf("--verbosity=%s", p.Build.Verbosity))
 	}
 
+	if p.Build.Platform != "" {
+		cmdArgs = append(cmdArgs, fmt.Sprintf("--customPlatform=%s", p.Build.Platform))
+	}
+
 	cmd := exec.Command("/kaniko/executor", cmdArgs...)
 	cmd.Stdout = os.Stdout
 	cmd.Stderr = os.Stderr

kaniko_test.go

@@ -1 +1,74 @@
 package kaniko
+
+import (
+	"testing"
+
+	"github.com/google/go-cmp/cmp"
+)
+
+func TestBuild_labelsForTag(t *testing.T) {
+	tests := []struct {
+		name     string
+		tag      string
+		autoTags []string
+	}{
+		{
+			name:     "semver",
+			tag:      "v1.2.3",
+			autoTags: []string{"1", "1.2", "1.2.3"},
+		},
+		{
+			name:     "no_patch",
+			tag:      "v1.2",
+			autoTags: []string{"1", "1.2", "1.2.0"},
+		},
+		{
+			name:     "only_major",
+			tag:      "v1",
+			autoTags: []string{"1", "1.0", "1.0.0"},
+		},
+		{
+			name:     "full_with_build",
+			tag:      "v1.2.3+build-info",
+			autoTags: []string{"1+build-info", "1.2+build-info", "1.2.3+build-info"},
+		},
+		{
+			name:     "build_with_underscores",
+			tag:      "v1.2.3+linux_amd64",
+			autoTags: []string{"1+linux-amd64", "1.2+linux-amd64", "1.2.3+linux-amd64"},
+		},
+		{
+			name:     "prerelease",
+			tag:      "v1.2.3-rc1",
+			autoTags: []string{"1.2.3-rc1"},
+		},
+		{
+			name:     "prerelease_with_build",
+			tag:      "v1.2.3-rc1+bld",
+			autoTags: []string{"1.2.3-rc1+bld"},
+		},
+		{
+			name:     "invalid_build",
+			tag:      "v1+bld", // can only include build detail with all three elements
+			autoTags: []string{"v1+bld"},
+		},
+		{
+			name:     "accidental_non_semver",
+			tag:      "1.2.3",
+			autoTags: []string{"1", "1.2", "1.2.3"},
+		},
+		{
+			name:     "non_semver",
+			tag:      "latest",
+			autoTags: []string{"latest"},
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			tags := Build{AutoTag: true}.labelsForTag(tt.tag)
+			if got, want := tags, tt.autoTags; !cmp.Equal(got, want) {
+				t.Errorf("tagsFor(%q) = %q, want %q", tt.tag, got, want)
+			}
+		})
+	}
+}