Use return value 1 always if there are linter errors

CHANGES.rst

@@ -9,6 +9,8 @@ Added
 - In the future test, upgrade ``Pygments`` to repository ``master``.
 - Messages from future test are now generic, not Black-specific.
 - Require ``click`` when running tests.
+- Linter failures now result in an exit value of 1. This makes Graylint compatible with
+  ``pre-commit``.
 
 Removed
 -------

action/tests/test_main.py → action/tests/test_action_main.py

@@ -88,14 +88,10 @@ def test_creates_virtualenv(tmp_path, main_patch):
 
 @pytest.mark.kwparametrize(
     dict(run_main_env={}, expect=["graylint[color]"]),
-    dict(
-        run_main_env={"INPUT_VERSION": "1.5.0"}, expect=["graylint[color]==1.5.0"]
-    ),
+    dict(run_main_env={"INPUT_VERSION": "1.5.0"}, expect=["graylint[color]==1.5.0"]),
     dict(
         run_main_env={"INPUT_VERSION": "@main"},
-        expect=[
-            "git+https://github.com/akaihola/graylint@main#egg=graylint[color]"
-        ],
+        expect=["git+https://github.com/akaihola/graylint@main#egg=graylint[color]"],
     ),
     dict(
         run_main_env={"INPUT_LINT": "pylint"},

pyproject.toml

@@ -12,6 +12,7 @@ target-version = ["py38", "py39", "py310", "py311", "py312"]
 # Darker makes isort read its configuration from the file indicated by the `--config`
 # option, so we need to mirror the same configuration here and in `check-graylint.toml`.
 profile = "black"
+known_first_party = ["darkgraylib", "graylint"]
 known_third_party = ["pytest"]
 
 [tool.darker]
@@ -42,10 +43,14 @@ ignore = [
 ]
 
 [tool.ruff.lint.per-file-ignores]
-"src/darker/tests/*.py" = [
+"src/graylint/tests/*.py" = [
     "ANN001",  # Missing type annotation for function argument
     "ANN201",  # Missing return type annotation for public function
     "ANN204",  # Missing return type annotation for special method `__init__`
     "C408",  # Unnecessary `dict` call (rewrite as a literal)
     "S101",  # Use of `assert` detected
 ]
+
+[tool.ruff.lint.isort]
+known-first-party = ["darkgraylib", "graylint"]
+known-third-party = ["pytest"]

src/graylint/__main__.py

@@ -1,5 +1,7 @@
 """Graylint - run linters and hide linter errors already present in previous revision"""
 
+from __future__ import annotations
+
 import logging
 import sys
 from argparse import ArgumentError
@@ -10,12 +12,10 @@
 from darkgraylib.highlighting import should_use_color
 from darkgraylib.log import setup_logging
 from darkgraylib.main import resolve_paths
-
 from graylint.command_line import make_argument_parser
 from graylint.config import GraylintConfig
 from graylint.linting import run_linters
 
-
 logger = logging.getLogger(__name__)
 
 
@@ -29,14 +29,14 @@ def main_with_error_handling() -> int:
         sys.exit(str(exc_info))
 
 
-def main() -> int:
+def main(argv: list[str] = None) -> int:
     """Parse the command line and lint each source file
 
     :return: Total number of linting errors found on modified lines
 
     """
     args, config, config_nondefault = parse_command_line(
-        make_argument_parser, sys.argv[1:], "graylint", GraylintConfig
+        make_argument_parser, argv, "graylint", GraylintConfig
     )
     setup_logging(args.log_level)
     show_config_if_debug(config, config_nondefault, args.log_level)
@@ -52,7 +52,7 @@ def main() -> int:
         revrange,
         use_color=should_use_color(config["color"]),
     )
-    return linter_failures_on_modified_lines
+    return 1 if linter_failures_on_modified_lines else 0
 
 
 if __name__ == "__main__":

src/graylint/tests/test_main.py

@@ -0,0 +1,36 @@
+"""Tests for the `graylint.__main__` module."""
+
+from unittest.mock import Mock, patch
+
+import pytest
+
+from graylint.__main__ import main
+
+
+@pytest.mark.kwparametrize(
+    dict(numfails=0, expect_retval=0),
+    dict(numfails=1, expect_retval=1),
+    dict(numfails=2, expect_retval=1),
+)
+def test_main_retval(numfails, expect_retval):
+    """main() return value is correct based on linter results."""
+    with patch("graylint.__main__.run_linters", Mock(return_value=numfails)):
+        # end of test setup
+
+        retval = main(["a.py"])
+
+    assert retval == expect_retval
+
+
+@pytest.mark.kwparametrize(
+    dict(arguments=[], expect_retval=0),
+    dict(arguments=["--lint", "echo subdir/a.py:1: message"], expect_retval=1),
+)
+def test_main(git_repo, arguments, expect_retval):
+    """Main function return value is 1 if there are linter errors."""
+    paths = git_repo.add({"subdir/a.py": "\n"}, commit="Initial commit")
+    paths["subdir/a.py"].write_text("Foo\n")
+
+    retval = main([*arguments, str(git_repo.root)])
+
+    assert retval == expect_retval