Fix the CurrentBranchName function

The function would return "head/branchname" when there was either a tag or a
remote with the same name.

While fixing this we slightly change the semantic of the function (and of
determineCheckedOutBranchName, which calls it): for a detached head it now
returns an empty string rather than the commit hash. I actually think this is
better.

pkg/commands/git_commands/branch.go

@@ -102,12 +102,10 @@ func (self *BranchCommands) CurrentBranchInfo() (BranchInfo, error) {
 	}, nil
 }
 
-// CurrentBranchName get name of current branch
+// CurrentBranchName get name of current branch. Returns empty string if HEAD is detached.
 func (self *BranchCommands) CurrentBranchName() (string, error) {
-	cmdArgs := NewGitCmd("rev-parse").
-		Arg("--abbrev-ref").
-		Arg("--verify").
-		Arg("HEAD").
+	cmdArgs := NewGitCmd("branch").
+		Arg("--show-current").
 		ToArgv()
 
 	output, err := self.cmd.New(cmdArgs).DontLog().RunWithOutput()

pkg/gui/controllers/helpers/refresh_helper.go

@@ -308,7 +308,7 @@ func (self *RefreshHelper) determineCheckedOutBranchName() string {
 	// In all other cases, get the branch name by asking git what branch is
 	// checked out. Note that if we're on a detached head (for reasons other
 	// than rebasing or bisecting, i.e. it was explicitly checked out), then
-	// this will return its hash.
+	// this will return an empty string.
 	if branchName, err := self.c.Git().Branch.CurrentBranchName(); err == nil {
 		return branchName
 	}

pkg/integration/tests/commit/do_not_show_branch_marker_for_head_commit.go

@@ -26,7 +26,7 @@ var DoNotShowBranchMarkerForHeadCommit = NewIntegrationTest(NewIntegrationTestAr
 		// Check that the local commits view does show a branch marker for the head commit
 		t.Views().Commits().
 			Lines(
-				Contains("CI * three"), // don't want the star here
+				Contains("CI three"),
 				Contains("CI two"),
 				Contains("CI branch1 one"),
 			)