internal/git: allow specific ref to be used in LastCommitMessage()

LastCommitMessage was querying for the last commit message from HEAD
only, hard-coded. So if the user uses --source option for creating an MR
that doesn't match with the branch he's checked-out the commit log
prompted will be from HEAD instead of what's present in the requested
source remote:branch through --source option.

Signed-off-by: Bruno Meneguele <[email protected]>

cmd/mr_create.go

@@ -292,7 +292,7 @@ func mrText(sourceRemote, sourceBranch, targetRemote, targetBranch string, cover
 	numCommits := git.NumberCommits(target, source)
 	if numCommits == 1 {
 		var err error
-		commitMsg, err = git.LastCommitMessage()
+		commitMsg, err = git.LastCommitMessage(source)
 		if err != nil {
 			return "", err
 		}

internal/git/git.go

@@ -108,8 +108,8 @@ func PagerCommand() (string, []string) {
 }
 
 // LastCommitMessage returns the last commits message as one line
-func LastCommitMessage() (string, error) {
-	cmd := New("show", "-s", "--format=%s%n%+b", "HEAD")
+func LastCommitMessage(sha string) (string, error) {
+	cmd := New("show", "-s", "--format=%s%n%+b", sha)
 	cmd.Stdout = nil
 	msg, err := cmd.Output()
 	if err != nil {

internal/git/git_test.go

@@ -63,7 +63,7 @@ func TestCommentChar(t *testing.T) {
 }
 
 func TestLastCommitMessage(t *testing.T) {
-	lcm, err := LastCommitMessage()
+	lcm, err := LastCommitMessage("HEAD")
 	if err != nil {
 		t.Fatal(err)
 	}