feat(clang-tidy): add --fix opt-in flag for auto-applying fixes in place

README.md

@@ -192,6 +192,28 @@ Use -header-filter=.* to display errors from all non-system headers. Use -system
 
 ```
 
+> [!NOTE]
+> Add `--fix` to `args` to automatically apply clang-tidy fixes in place (equivalent to
+> passing `-fix` to clang-tidy directly). This is **opt-in** and **not the default** because
+> auto-fixing can modify source files in unexpected ways. A valid `compile_commands.json` is
+> strongly recommended when using `--fix`.
+>
+> For cases where compiler errors exist alongside style issues, pass `-fix-errors` directly
+> in `args` instead (clang-tidy native flag).
+
+```yaml
+repos:
+  - repo: https://github.com/cpp-linter/cpp-linter-hooks
+    rev: v1.2.0
+    hooks:
+      - id: clang-tidy
+        args: [--checks=.clang-tidy, --fix]
+```
+
+> [!WARNING]
+> When `--fix` (or `-fix-errors`) is active, parallel execution via `--jobs`/`-j` is
+> automatically disabled to prevent concurrent writes to the same header file.
+
 ## Troubleshooting
 
 ### Performance Optimization
@@ -266,6 +288,7 @@ repos:
 | Supports passing format style string | ✅ via `--style`                      | ❌                                    |
 | Verbose output                   | ✅ via `--verbose`                        | ❌                                    |
 | Dry-run mode                     | ✅ via `--dry-run`                        | ❌                                    |
+| Auto-fix mode                    | ✅ via `--fix` (clang-tidy only)          | ❌                                    |
 | Compilation database support     | ✅ auto-detect or `--compile-commands`    | ❌                                    |
 
 

cpp_linter_hooks/clang_tidy.py

@@ -45,6 +45,7 @@ def _positive_int(value: str) -> int:
 )
 parser.add_argument("-j", "--jobs", type=_positive_int, default=1)
 parser.add_argument("-v", "--verbose", action="store_true")
+parser.add_argument("--fix", action="store_true", help="Apply fixes in place (-fix)")
 
 
 def _find_compile_commands() -> Optional[str]:
@@ -154,11 +155,17 @@ def run_clang_tidy(args=None) -> Tuple[int, str]:
 
     clang_tidy_args, source_files = _split_source_files(other_args)
 
+    if hook_args.fix:
+        clang_tidy_args.append("-fix")
+
     # Parallel execution is unsafe when arguments include flags that write to a
-    # shared output path (e.g., --export-fixes fixes.yaml). In that case, force
-    # serial execution to avoid concurrent writes/overwrites.
+    # shared output path (e.g., --export-fixes fixes.yaml) or that apply in-place
+    # fixes (-fix, -fix-errors), since multiple clang-tidy processes may attempt
+    # to modify the same header file concurrently.
     unsafe_parallel = any(
-        arg == "--export-fixes" or arg.startswith("--export-fixes=")
+        arg == "--export-fixes"
+        or arg.startswith("--export-fixes=")
+        or arg in ("-fix", "-fix-errors")
         for arg in clang_tidy_args
     )
 
@@ -167,7 +174,7 @@ def run_clang_tidy(args=None) -> Tuple[int, str]:
             ["clang-tidy"] + clang_tidy_args, source_files, hook_args.jobs
         )
 
-    return _exec_clang_tidy(["clang-tidy"] + other_args)
+    return _exec_clang_tidy(["clang-tidy"] + clang_tidy_args + source_files)
 
 
 def main() -> int:

tests/test_clang_tidy.py

@@ -324,3 +324,50 @@ def test_jobs_with_export_fixes_forces_serial_execution():
             "b.cpp",
         ]
     )
+
+
+def test_fix_flag_appends_fix_to_command():
+    with (
+        patch(
+            "cpp_linter_hooks.clang_tidy._exec_clang_tidy", return_value=(0, "")
+        ) as mock_exec,
+        patch("cpp_linter_hooks.clang_tidy.resolve_install"),
+    ):
+        run_clang_tidy(["--fix", "-p", "./build", "dummy.cpp"])
+
+    cmd = mock_exec.call_args[0][0]
+    assert "-fix" in cmd
+
+
+def test_fix_flag_forces_serial_execution():
+    with (
+        patch(
+            "cpp_linter_hooks.clang_tidy._exec_clang_tidy", return_value=(0, "")
+        ) as mock_exec,
+        patch("cpp_linter_hooks.clang_tidy.resolve_install"),
+    ):
+        run_clang_tidy(["--fix", "--jobs=4", "-p", "./build", "a.cpp", "b.cpp"])
+
+    mock_exec.assert_called_once()
+    cmd = mock_exec.call_args[0][0]
+    assert "-fix" in cmd
+    assert "a.cpp" in cmd
+    assert "b.cpp" in cmd
+
+
+def test_fix_errors_in_args_forces_serial_execution():
+    with (
+        patch(
+            "cpp_linter_hooks.clang_tidy._exec_clang_tidy", return_value=(0, "")
+        ) as mock_exec,
+        patch("cpp_linter_hooks.clang_tidy.resolve_install"),
+    ):
+        run_clang_tidy(
+            ["--jobs=4", "-p", "./build", "-fix-errors", "a.cpp", "b.cpp"]
+        )
+
+    mock_exec.assert_called_once()
+    cmd = mock_exec.call_args[0][0]
+    assert "-fix-errors" in cmd
+    assert "a.cpp" in cmd
+    assert "b.cpp" in cmd