Added option to manually specifiy project root

src/black/__init__.py

@@ -357,6 +357,17 @@ def validate_regex(
         "editors that rely on using stdin."
     ),
 )
+@click.option(
+    "--project-root",
+    type=click.Path(
+        exists=True, file_okay=False, dir_okay=True, readable=True, allow_dash=True
+    ),
+    help=(
+        "Manually specifiy the project root. This will prevent black from searching "
+        "for the project root itself. Useful to prevent black from picking up git "
+        "submodules as the project root which can affect the exclude behaviour."
+    ),
+)
 @click.option(
     "-W",
     "--workers",
@@ -438,6 +449,7 @@ def main(  # noqa: C901
     extend_exclude: Optional[Pattern[str]],
     force_exclude: Optional[Pattern[str]],
     stdin_filename: Optional[str],
+    project_root: Optional[str],
     workers: int,
     src: Tuple[str, ...],
     config: Optional[str],
@@ -455,7 +467,15 @@ def main(  # noqa: C901
         out(main.get_usage(ctx) + "\n\nOne of 'SRC' or 'code' is required.")
         ctx.exit(1)
 
-    root, method = find_project_root(src) if code is None else (None, None)
+    if project_root:
+        project_root_abs = Path(project_root).resolve()
+        root, method = (
+            (project_root_abs, "manually-specified project root")
+            if code is None
+            else (None, None)
+        )
+    else:
+        root, method = find_project_root(src) if code is None else (None, None)
     ctx.obj["root"] = root
 
     if verbose:

tests/test_black.py

@@ -1852,8 +1852,11 @@ def assert_collected_sources(
         None if extend_exclude is None else compile_pattern(extend_exclude)
     )
     gs_force_exclude = None if force_exclude is None else compile_pattern(force_exclude)
+    if not ctx:
+        ctx = FakeContext()
+    ctx.obj["root"], _ = black.find_project_root(gs_src)
     collected = black.get_sources(
-        ctx=ctx or FakeContext(),
+        ctx=ctx,
         src=gs_src,
         quiet=False,
         verbose=False,
@@ -2016,6 +2019,20 @@ def test_extend_exclude(self) -> None:
             src, expected, exclude=r"\.pyi$", extend_exclude=r"\.definitely_exclude"
         )
 
+    def test_git_submodule_exclude_full_path(self) -> None:
+        path = DATA_DIR / "git_submodule_exclude_tests" / "excluded_submodule" / "a.py"
+        src = [path]
+        expected: List[str] = []
+        assert_collected_sources(src, expected, force_exclude=r"excluded_submodule")
+
+    def test_git_submodule_exclude_base_path(self) -> None:
+        path = DATA_DIR / "git_submodule_exclude_tests"
+        src = [path]
+        expected = [
+            Path(path / "a.py"),
+        ]
+        assert_collected_sources(src, expected, force_exclude=r"excluded_submodule")
+
     @pytest.mark.incompatible_with_mypyc
     def test_symlink_out_of_root_directory(self) -> None:
         path = MagicMock()