feat: detect target branch using standard Git configuration

The current code forces the user to choose a single target branch which
prevents stacks from working on multiple target branches. This leverage
the standard git configuration to retrieve the target branch.

Change-Id: Ia1455d68eaa76af503b6e6cf4c24c19efcdd9b7b

mergify_cli/__init__.py

@@ -437,42 +437,60 @@ async def log_httpx_response(response: httpx.Response) -> None:  # noqa: RUF029
     )
 
 
-def get_trunk() -> str:
-    try:
-        trunk = subprocess.check_output(
-            "git config --get mergify-cli.stack-trunk",
-            shell=True,
-            text=True,
-        ).strip()
-    except subprocess.CalledProcessError:
-        trunk = ""
+def git_get_branch_name() -> str:
+    return subprocess.check_output(
+        ["git", "rev-parse", "--abbrev-ref", "HEAD"],
+        text=True,
+    ).strip()
 
-    if not trunk:
-        try:
-            dest_branch = subprocess.check_output(
-                "git rev-parse --abbrev-ref HEAD",
-                shell=True,
-                text=True,
-            ).strip()
-        except subprocess.CalledProcessError:
-            return ""
 
-        try:
-            trunk = subprocess.check_output(
-                f"git for-each-ref --format='%(upstream:short)' refs/heads/{dest_branch}",
-                shell=True,
-                text=True,
-            ).strip()
-        except subprocess.CalledProcessError:
-            trunk = ""
+def git_get_target_branch(branch: str) -> str:
+    target_branch = subprocess.check_output(
+        ["git", "config", "--get", "branch." + branch + ".merge"],
+        text=True,
+    ).strip()
+
+    return target_branch.removeprefix("refs/heads/")
+
 
-    return trunk
+def git_get_remote_for_branch(branch: str) -> str:
+    return subprocess.check_output(
+        ["git", "config", "--get", "branch." + branch + ".remote"],
+        text=True,
+    ).strip()
+
+
+def get_trunk() -> str:
+    try:
+        branch_name = git_get_branch_name()
+    except subprocess.CalledProcessError:
+        console.print("error: can't get the current branch", style="red")
+        raise
+    try:
+        target_branch = git_get_target_branch(branch_name)
+    except subprocess.CalledProcessError:
+        # It's possible this has not been set; ignore
+        console.print("error: can't get the remote target branch", style="red")
+        console.print(
+            f"Please set the target branch with `git branch {branch_name} --set-upstream-to=<remote>/<branch>",
+            style="red",
+        )
+        raise
+    try:
+        remote = git_get_remote_for_branch(target_branch)
+    except subprocess.CalledProcessError:
+        console.print(
+            f"error: can't get the remote for branch {target_branch}",
+            style="red",
+        )
+        raise
+    return f"{remote}/{target_branch}"
 
 
 def trunk_type(trunk: str) -> tuple[str, str]:
     result = trunk.split("/", maxsplit=1)
     if len(result) != 2:
-        msg = "stack-trunk is invalid. It must be origin/branch-name [/]"
+        msg = "Trunk is invalid. It must be origin/branch-name [/]"
         raise argparse.ArgumentTypeError(msg)
     return result[0], result[1]
 
@@ -809,8 +827,7 @@ def parse_args(args: typing.MutableSequence[str]) -> argparse.Namespace:
         "-t",
         type=trunk_type,
         default=get_trunk(),
-        help="Change the target branch of the stack. "
-        "Default fetched from git config if added with `git config --add mergify-cli.stack-trunk origin/branch-name`",
+        help="Change the target branch of the stack.",
     )
     stack_parser.add_argument(
         "--branch-prefix",

mergify_cli/tests/test_mergify_cli.py

@@ -36,6 +36,16 @@ def _change_working_directory(
     monkeypatch.chdir(tmp_path)
 
 
+@pytest.fixture()
+def _git_repo() -> None:
+    subprocess.call(["git", "init", "--initial-branch=main"])
+    subprocess.call(["git", "config", "user.email", "[email protected]"])
+    subprocess.call(["git", "config", "user.name", "Test User"])
+    subprocess.call(["git", "commit", "--allow-empty", "-m", "Initial commit"])
+    subprocess.call(["git", "config", "--add", "branch.main.merge", "refs/heads/main"])
+    subprocess.call(["git", "config", "--add", "branch.main.remote", "origin"])
+
+
 @pytest.fixture()
 def git_mock(
     tmp_path: pathlib.Path,
@@ -58,6 +68,7 @@ def git_mock(
         yield git_mock_object
 
 
+@pytest.mark.usefixtures("_git_repo")
 def test_cli_help(capsys: pytest.CaptureFixture[str]) -> None:
     with pytest.raises(SystemExit, match="0"):
         mergify_cli.parse_args(["--help"])
@@ -68,6 +79,26 @@ def test_cli_help(capsys: pytest.CaptureFixture[str]) -> None:
     assert "options:" in stdout
 
 
+@pytest.mark.usefixtures("_git_repo")
+def test_get_branch_name() -> None:
+    assert mergify_cli.git_get_branch_name() == "main"
+
+
+@pytest.mark.usefixtures("_git_repo")
+def test_get_target_branch() -> None:
+    assert mergify_cli.git_get_target_branch("main") == "main"
+
+
+@pytest.mark.usefixtures("_git_repo")
+def test_get_remote_for_branch() -> None:
+    assert mergify_cli.git_get_remote_for_branch("main") == "origin"
+
+
+@pytest.mark.usefixtures("_git_repo")
+def test_get_trunk() -> None:
+    assert mergify_cli.get_trunk() == "origin/main"
+
+
 @pytest.mark.parametrize(
     "valid_branch_name",
     [
@@ -533,7 +564,6 @@ async def test_stack_without_common_commit_raises_an_error(
     ("default_arg_fct", "config_get_result", "expected_default"),
     [
         (mergify_cli.get_default_keep_pr_title_body, b"true", True),
-        (mergify_cli.get_trunk, "dummy-origin/main", "dummy-origin/main"),
         (mergify_cli.get_default_branch_prefix, b"dummy-prefix", "dummy-prefix"),
     ],
 )

pyproject.toml

@@ -108,6 +108,8 @@ ignore = [
     "S404",
     # NOTE(charly): `subprocess` call with `shell=True`
     "S602",
+    # NOTE(jd): likely a false positive https://github.com/PyCQA/bandit/issues/333
+    "S603",
     # NOTE(charly): Starting a process with a partial executable path
     "S607",
     # NOTE(charly): Boolean-typed positional argument in function definition.