Set DockerRepo PublishOption from KO_DOCKER_REPO

This enables programmatically setting the destination image repository
and avoids exposing a flag.

Author: halvards

README.md

@@ -61,13 +61,12 @@ to
 
 ## Choose Destination
 
-`ko` must be configured with a destination for where it should push images that
-it builds. You can configure this with either the `--docker-repo` flag or the
-`KO_DOCKER_REPO` environment variable. Typically, the value will be a remote
-registry, e.g.:
+`ko` depends on an environment variable, `KO_DOCKER_REPO`, to identify where it
+should push images that it builds. Typically this will be a remote registry,
+e.g.:
 
 - `KO_DOCKER_REPO=gcr.io/my-project`, or
-- `--docker-repo=my-dockerhub-user`
+- `KO_DOCKER_REPO=my-dockerhub-user`
 
 If both the flag and the environment variable are set, the flag value takes
 precedence.

pkg/commands/options/publish.go

@@ -17,6 +17,7 @@ package options
 import (
 	"crypto/md5" //nolint: gosec // No strong cryptography needed.
 	"encoding/hex"
+	"os"
 	"path"
 
 	"github.com/google/ko/pkg/publish"
@@ -49,7 +50,11 @@ type PublishOptions struct {
 }
 
 func AddPublishArg(cmd *cobra.Command, po *PublishOptions) {
-	cmd.Flags().StringVar(&po.DockerRepo, "docker-repo", "", "Repository to push images, overrides KO_DOCKER_REPO")
+	// Set DockerRepo from the KO_DOCKER_REPO envionment variable.
+	// See https://github.com/google/ko/pull/351 for flag discussion.
+	if dockerRepo, exists := os.LookupEnv("KO_DOCKER_REPO"); exists {
+		po.DockerRepo = dockerRepo
+	}
 
 	cmd.Flags().StringSliceVarP(&po.Tags, "tags", "t", []string{"latest"},
 		"Which tags to use for the produced image instead of the default 'latest' tag "+

pkg/commands/resolver.go

@@ -131,10 +131,7 @@ func makePublisher(po *options.PublishOptions) (publish.Interface, error) {
 	// Create the publish.Interface that we will use to publish image references
 	// to either a docker daemon or a container image registry.
 	innerPublisher, err := func() (publish.Interface, error) {
-		repoName := os.Getenv("KO_DOCKER_REPO")
-		if po.DockerRepo != "" {
-			repoName = po.DockerRepo
-		}
+		repoName := po.DockerRepo
 		namer := options.MakeNamer(po)
 		if repoName == publish.LocalDomain || po.Local {
 			// TODO(jonjohnsonjr): I'm assuming that nobody will
@@ -147,7 +144,7 @@ func makePublisher(po *options.PublishOptions) (publish.Interface, error) {
 		}
 
 		if repoName == "" {
-			return nil, errors.New("either --docker-repo flag or KO_DOCKER_REPO environment variable must be set")
+			return nil, errors.New("KO_DOCKER_REPO environment variable is unset")
 		}
 		if _, err := name.NewRegistry(repoName); err != nil {
 			if _, err := name.NewRepository(repoName); err != nil {