fork: Allow forking from remotes other than "origin"

The fork command can be used in two ways:

 1. when passed a namespaced project name (e.g. "SomeGroup/AwesomeProject"),
    the project is forked (and optionally cloned)
 2. without arguments, the project name is determined from the "origin"
    remote in the current repository, forked and added as remote

The second mode currently doesn't work if the repository pointed to by
"origin" doesn't use the Namespace/Project structure gitlab expects.

Support that use case by also picking the second mode when the passed
argument corresponds to an existing remote.

Fixes #563

cmd/fork.go

@@ -25,7 +25,7 @@ var (
 
 // forkCmd represents the fork command
 var forkCmd = &cobra.Command{
-	Use:              "fork [upstream-to-fork]",
+	Use:              "fork [remote|upstream-to-fork]",
 	Short:            "Fork a remote repository on GitLab and add as remote",
 	Long:             ``,
 	Args:             cobra.MaximumNArgs(1),
@@ -47,15 +47,33 @@ var forkCmd = &cobra.Command{
 			}
 		}
 
+		remote, project := "", ""
 		if len(args) == 1 {
-			forkToUpstream(args[0])
+			if ok, _ := git.IsRemote(args[0]); ok {
+				remote = args[0]
+			} else {
+				project = args[0]
+			}
+		}
+
+		if project != "" {
+			forkToUpstream(project)
 			return
 		}
-		forkFromOrigin()
+
+		if remote == "" {
+			remote = "origin"
+		}
+
+		project, err := git.PathWithNameSpace(remote)
+		if err != nil {
+			log.Fatal(err)
+		}
+		forkFromOrigin(project)
 	},
 }
 
-func forkFromOrigin() {
+func forkFromOrigin(project string) {
 	// Check for custom target namespace
 	remote := lab.User()
 	if targetData.group != "" {
@@ -82,11 +100,6 @@ func forkFromOrigin() {
 		return
 	}
 
-	project, err := git.PathWithNameSpace("origin")
-	if err != nil {
-		log.Fatal(err)
-	}
-
 	forkRemoteURL, err := lab.Fork(project, forkOpts, useHTTP, waitFork)
 	if err != nil {
 		if err.Error() == "not finished" {