Detect git worktrees and submodules in identify_vcs

flit/vcs/__init__.py

@@ -6,7 +6,11 @@
 def identify_vcs(directory: Path):
     directory = directory.resolve()
     for p in [directory] + list(directory.parents):
-        if (p / '.git').is_dir():
+        # In a linked git worktree (`git worktree add ...`) or inside a
+        # git submodule, `.git` is a regular file containing a
+        # `gitdir: <path>` pointer rather than a directory.
+        git_entry = p / '.git'
+        if git_entry.is_dir() or git_entry.is_file():
             return git
         if (p / '.hg').is_dir():
             return hg

tests/test_vcs.py

@@ -24,3 +24,14 @@ def test_identify_git_parent():
         subdir.mkdir()
         with cwd(subdir):
             assert vcs.identify_vcs(Path('.')).name == 'git'
+
+def test_identify_git_worktree():
+    # In a linked git worktree (or submodule) `.git` is a regular file
+    # containing a `gitdir:` pointer rather than a directory.
+    with TemporaryDirectory() as td:
+        td = Path(td)
+        (td / '.git').write_text('gitdir: /path/to/main/.git/worktrees/feature\n')
+        subdir = (td / 'subdir')
+        subdir.mkdir()
+        with cwd(subdir):
+            assert vcs.identify_vcs(Path('.')).name == 'git'