Present a more user-friendly error if .gitignore is invalid

Fixes #2359

CHANGES.md

@@ -6,6 +6,7 @@
 
 - Add support for formatting Jupyter Notebook files (#2357)
 - Move from `appdirs` dependency to `platformdirs` (#2375)
+- Present a more user-friendly error if .gitignore is invalid (#2414)
 
 ## 21.7b0
 

setup.py

@@ -77,7 +77,7 @@ def get_long_description() -> str:
         "tomli>=0.2.6,<2.0.0",
         "typed-ast>=1.4.2; python_version < '3.8'",
         "regex>=2020.1.8",
-        "pathspec>=0.8.1, <1",
+        "pathspec>=0.9.0, <1",
         "dataclasses>=0.6; python_version < '3.7'",
         "typing_extensions>=3.10.0.0; python_version < '3.10'",
         "mypy_extensions>=0.4.3",

src/black/__init__.py

@@ -495,6 +495,8 @@ def get_sources(
     if exclude is None:
         exclude = re_compile_maybe_verbose(DEFAULT_EXCLUDES)
         gitignore = get_gitignore(root)
+        if gitignore is None:
+            ctx.exit(1)
     else:
         gitignore = None
 

src/black/files.py

@@ -18,6 +18,7 @@
 )
 
 from pathspec import PathSpec
+from pathspec.patterns.gitwildmatch import GitWildMatchPatternError
 import tomli
 
 from black.output import err
@@ -122,7 +123,11 @@ def get_gitignore(root: Path) -> PathSpec:
     if gitignore.is_file():
         with gitignore.open(encoding="utf-8") as gf:
             lines = gf.readlines()
-    return PathSpec.from_lines("gitwildmatch", lines)
+    try:
+        return PathSpec.from_lines("gitwildmatch", lines)
+    except GitWildMatchPatternError as e:
+        err(f"Could not parse {gitignore}: {e}")
+        return None
 
 
 def normalize_path_maybe_ignore(

tests/data/invalid_gitignore_tests/.gitignore

@@ -0,0 +1 @@
+!

tests/data/invalid_gitignore_tests/pyproject.toml

@@ -0,0 +1 @@
+# Empty configuration file; used in tests to avoid interference from Black's own config.

tests/test_black.py

@@ -1727,6 +1727,18 @@ def test_nested_gitignore(self) -> None:
         )
         self.assertEqual(sorted(expected), sorted(sources))
 
+    def test_invalid_gitignore(self) -> None:
+        path = THIS_DIR / "data" / "invalid_gitignore_tests"
+        empty_config = THIS_DIR / "data" / "invalid_gitignore_tests" / "pyproject.toml"
+        result = BlackRunner().invoke(
+            black.main, ["--verbose", "--config", str(empty_config), str(path)]
+        )
+        assert result.exit_code == 1
+        assert result.stderr_bytes is not None
+
+        gitignore = path / ".gitignore"
+        assert f"Could not parse {gitignore}" in result.stderr_bytes.decode()
+
     def test_empty_include(self) -> None:
         path = THIS_DIR / "data" / "include_exclude_tests"
         report = black.Report()