feat: allow templates on docker tags

Allow to template docker tags.

Closes #433

pipeline/docker/docker_test.go

@@ -40,50 +40,88 @@ func TestRunPipe(t *testing.T) {
 	var binPath = filepath.Join(dist, "mybin", "mybin")
 	_, err = os.Create(binPath)
 	assert.NoError(t, err)
+
+	var table = map[string]struct {
+		docker config.Docker
+		err    string
+	}{
+		"valid": {
+			docker: config.Docker{
+				Image:       "localhost:5000/goreleaser/test_run_pipe",
+				Goos:        "linux",
+				Goarch:      "amd64",
+				Dockerfile:  "testdata/Dockerfile",
+				Binary:      "mybin",
+				Latest:      true,
+				TagTemplate: "{{.Tag}}",
+			},
+			err: "",
+		},
+		"invalid": {
+			docker: config.Docker{
+				Image:       "localhost:5000/goreleaser/test_run_pipe_nope",
+				Goos:        "linux",
+				Goarch:      "amd64",
+				Dockerfile:  "testdata/Dockerfile",
+				Binary:      "otherbin",
+				TagTemplate: "{{.Version}}",
+			},
+			err: "",
+		},
+		"template_error": {
+			docker: config.Docker{
+				Image:       "localhost:5000/goreleaser/test_run_pipe_template_error",
+				Goos:        "linux",
+				Goarch:      "amd64",
+				Dockerfile:  "testdata/Dockerfile",
+				Binary:      "mybin",
+				Latest:      true,
+				TagTemplate: "{{.Tag}",
+			},
+			err: `template: tag:1: unexpected "}" in operand; missing space?`,
+		},
+	}
 	var images = []string{
-		"localhost:5000/goreleaser/test_run_pipe:1.0.0",
+		"localhost:5000/goreleaser/test_run_pipe:v1.0.0",
 		"localhost:5000/goreleaser/test_run_pipe:latest",
 	}
 	// this might fail as the image doesnt exist yet, so lets ignore the error
 	for _, img := range images {
 		_ = exec.Command("docker", "rmi", img).Run()
 	}
-	var ctx = &context.Context{
-		Version: "1.0.0",
-		Publish: true,
-		Config: config.Project{
-			ProjectName: "mybin",
-			Dist:        dist,
-			Dockers: []config.Docker{
-				{
-					Image:      "localhost:5000/goreleaser/test_run_pipe",
-					Goos:       "linux",
-					Goarch:     "amd64",
-					Dockerfile: "testdata/Dockerfile",
-					Binary:     "mybin",
-					Latest:     true,
+
+	for name, docker := range table {
+		t.Run(name, func(t *testing.T) {
+			var ctx = &context.Context{
+				Version: "1.0.0",
+				Publish: true,
+				Git: context.GitInfo{
+					CurrentTag: "v1.0.0",
 				},
-				{
-					Image:      "localhost:5000/goreleaser/test_run_pipe_nope",
-					Goos:       "linux",
-					Goarch:     "amd64",
-					Dockerfile: "testdata/Dockerfile",
-					Binary:     "otherbin",
+				Config: config.Project{
+					ProjectName: "mybin",
+					Dist:        dist,
+					Dockers: []config.Docker{
+						docker.docker,
+					},
 				},
-			},
-		},
+			}
+			for _, plat := range []string{"linuxamd64", "linux386", "darwinamd64"} {
+				ctx.AddBinary(plat, "mybin", "mybin", binPath)
+			}
+			if docker.err != "" {
+				assert.EqualError(t, Pipe{}.Run(ctx), docker.err)
+			} else {
+				assert.NoError(t, Pipe{}.Run(ctx))
+			}
+		})
 	}
-	for _, plat := range []string{"linuxamd64", "linux386", "darwinamd64"} {
-		ctx.AddBinary(plat, "mybin", "mybin", binPath)
-	}
-	assert.NoError(t, Pipe{}.Run(ctx))
 
 	// this might should not fail as the image should have been created when
 	// the step ran
 	for _, img := range images {
 		assert.NoError(t, exec.Command("docker", "rmi", img).Run())
 	}
-
 	// the test_run_pipe_nope image should not have been created, so deleting
 	// it should fail
 	assert.Error(t,
@@ -152,6 +190,7 @@ func TestDefault(t *testing.T) {
 	assert.Equal(t, "amd64", docker.Goarch)
 	assert.Equal(t, ctx.Config.Builds[0].Binary, docker.Binary)
 	assert.Equal(t, "Dockerfile", docker.Dockerfile)
+	assert.Equal(t, "{{ .Version }}", docker.TagTemplate)
 }
 
 func TestDefaultNoDockers(t *testing.T) {
@@ -183,5 +222,6 @@ func TestDefaultSet(t *testing.T) {
 	assert.Equal(t, "windows", docker.Goos)
 	assert.Equal(t, "i386", docker.Goarch)
 	assert.Equal(t, "bar", docker.Binary)
+	assert.Equal(t, "{{ .Version }}", docker.TagTemplate)
 	assert.Equal(t, "Dockerfile.foo", docker.Dockerfile)
 }