client.ImagePush(): default to ":latest" instead of "all tags"

The `docker push` command up until docker v0.9.1 always pushed all tags of a given
image, so `docker push foo/bar` would push (e.g.) all of  `foo/bar:latest`, `foo:/bar:v1`,
and `foo/bar:v1.0.0`.

Pushing all tags of an image was not desirable in many case, so docker v0.10.0
enhanced `docker push` to optionally specify a tag to push (`docker push foo/bar:v1`)
(see issue 3411 and PR 4948 (commit e648a186d6).

This behavior exists up until today, and is confusing, because unlike other commands,
`docker push` does not default to use the `:latest` tag when omitted, but instead
makes it push "all tags of the image".

`docker pull` had a similar behavior, but PR 7759 (9c08364a41)
changed the behavior to default to the `:latest` tag, and added a `--all-tags` flag
to the CLI to optionally pull all images.

This patch implements the API client changes to make `docker push` match the behavior
of `docker pull`, and default to pull a single image, unless the `all` option is passed.

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

client/image_push.go

@@ -25,15 +25,14 @@ func (cli *Client) ImagePush(ctx context.Context, image string, options types.Im
 		return nil, errors.New("cannot push a digest reference")
 	}
 
-	tag := ""
 	name := reference.FamiliarName(ref)
-
-	if nameTaggedRef, isNamedTagged := ref.(reference.NamedTagged); isNamedTagged {
-		tag = nameTaggedRef.Tag()
-	}
-
 	query := url.Values{}
-	query.Set("tag", tag)
+	if !options.All {
+		ref = reference.TagNameOnly(ref)
+		if tagged, ok := ref.(reference.Tagged); ok {
+			query.Set("tag", tagged.Tag())
+		}
+	}
 
 	resp, err := cli.tryImagePush(ctx, name, query, options.RegistryAuth)
 	if errdefs.IsUnauthorized(err) && options.PrivilegeFunc != nil {