[jj] Make JjWrapper support secondary JJ workspaces

This change makes JjWrapper a no-op for secondary JJ workspaces that do not have a .git directory or worktree. It now holds an instance of GitWrapper and forwards commands to it only if a .git directory or worktree exists.

In particular, this allows gclient sync to run in secondary workspaces without fetching the git repository for the root.

Change-Id: Id89a83d7ce193304847dd75bbffa133e6a6a6964
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/7780501
Commit-Queue: Sunny Sachanandani <sunnyps@chromium.org>
Auto-Submit: Sunny Sachanandani <sunnyps@chromium.org>
Reviewed-by: Matt Stark <msta@google.com>
Commit-Queue: Matt Stark <msta@google.com>

jj/scm.py

@@ -7,14 +7,61 @@ import subprocess
 import gclient_scm
 
 
-class JjWrapper(gclient_scm.GitWrapper):
+class JjWrapper(gclient_scm.SCMWrapper):
     """JjWrapper handles repos that are intended to be used with jj.
 
     The repo does not yet need to be using jj, and does not even need to exist.
     """
 
+    def __init__(self, url=None, *args, **kwargs):
+        super(JjWrapper, self).__init__(url, *args, **kwargs)
+        git_path = pathlib.Path(self.checkout_path, '.git')
+        if git_path.exists():
+            self._git_wrapper = gclient_scm.GitWrapper(url, *args, **kwargs)
+        else:
+            self._git_wrapper = None
+
+    def _check_git_wrapper(self, command):
+        if not self._git_wrapper:
+            self.Print(
+                f"Command '{command}' is not supported on JJ workspaces "
+                "without a .git directory or worktree file"
+            )
+            return False
+        return True
+
+    def update(self, options, args, file_list):
+        if self._check_git_wrapper('update'):
+            self._git_wrapper.update(options, args, file_list)
+
+    def revert(self, options, args, file_list):
+        if self._check_git_wrapper('revert'):
+            self._git_wrapper.revert(options, args, file_list)
+
+    def revinfo(self, options, args, file_list):
+        if self._check_git_wrapper('revinfo'):
+            self._git_wrapper.revinfo(options, args, file_list)
+
+    def status(self, options, args, file_list):
+        if self._check_git_wrapper('status'):
+            self._git_wrapper.status(options, args, file_list)
+
+    def diff(self, options, args, file_list):
+        if self._check_git_wrapper('diff'):
+            self._git_wrapper.diff(options, args, file_list)
+
+    def pack(self, options, args, file_list):
+        if self._check_git_wrapper('pack'):
+            self._git_wrapper.pack(options, args, file_list)
+
+    def runhooks(self, options, args, file_list):
+        if self._check_git_wrapper('runhooks'):
+            self._git_wrapper.runhooks(options, args, file_list)
+
+
     def _GetSubmodulePaths(self):
-        with pathlib.Path(self.checkout_path, '.gitmodules').open('r') as f:
+        gitmodules_path = pathlib.Path(self.checkout_path, '.gitmodules')
+        with gitmodules_path.open('r', encoding='utf-8') as f:
             for line in f:
                 line = line.strip()
                 if not line.startswith('path = '):