Implement support for `core.commentchar=auto`

117ddefdb4/builtin/commit.c (L633)

git/git.go

@@ -195,10 +195,23 @@ func (r *Range) IsAncestor() bool {
 func CommentChar(text string) (string, error) {
 	char, err := Config("core.commentchar")
 	if err != nil {
-		char = "#"
+		return "#", nil
+	} else if char == "auto" {
+		lines := strings.Split(text, "\n")
+		commentCharCandidates := strings.Split("#;@!$%^&|:", "")
+	candidateLoop:
+		for _, candidate := range commentCharCandidates {
+			for _, line := range lines {
+				if strings.HasPrefix(line, candidate) {
+					continue candidateLoop
+				}
+			}
+			return candidate, nil
+		}
+		return "", fmt.Errorf("unable to select a comment character that is not used in the current message")
+	} else {
+		return char, nil
 	}
-
-	return char, nil
 }
 
 func Show(sha string) (string, error) {

git/git_test.go

@@ -154,3 +154,33 @@ func TestRemotes(t *testing.T) {
 		}
 	}
 }
+
+func TestCommentChar(t *testing.T) {
+	repo := fixtures.SetupTestRepo()
+	defer repo.TearDown()
+
+	char, err := CommentChar("")
+	assert.Equal(t, nil, err)
+	assert.Equal(t, "#", char)
+
+	SetGlobalConfig("core.commentchar", ";")
+	char, err = CommentChar("")
+	assert.Equal(t, nil, err)
+	assert.Equal(t, ";", char)
+
+	SetGlobalConfig("core.commentchar", "auto")
+	char, err = CommentChar("")
+	assert.Equal(t, nil, err)
+	assert.Equal(t, "#", char)
+
+	char, err = CommentChar("hello\n#nice\nworld")
+	assert.Equal(t, nil, err)
+	assert.Equal(t, ";", char)
+
+	char, err = CommentChar("hello\n#nice\n;world")
+	assert.Equal(t, nil, err)
+	assert.Equal(t, "@", char)
+
+	char, err = CommentChar("#\n;\n@\n!\n$\n%\n^\n&\n|\n:")
+	assert.Equal(t, "unable to select a comment character that is not used in the current message", err.Error())
+}