feat: make maximum subject length configurable

README.md

@@ -80,6 +80,15 @@ Available checks:
 * `signed-off` - `Signed-off-by:` trailer exists
 * `signature` - Verify GPG or SSH signature
 
+### Subject length
+
+The default maximum subject line length is 72 characters. Override with
+`--max-subject-length`:
+
+```bash
+commit-guard --max-subject-length 100
+```
+
 ### Type validation
 
 By default the standard conventional commit types are accepted. Use `--types`
@@ -113,25 +122,27 @@ commit-guard --scopes auth,api --require-scope
 ### Configuration file
 
 Place `.commit-guard.toml` in your project root (or any parent directory) to
-set defaults for `enable`, `disable`, `scopes`, `require-scope`, and `types`.
-commit-guard searches upward from the working directory and uses the first file
-found.
+set defaults for `enable`, `disable`, `scopes`, `require-scope`, `types`, and
+`max-subject-length`. commit-guard searches upward from the working directory
+and uses the first file found.
 
 ```toml
 # .commit-guard.toml
 disable = ["signature", "body"]
 scopes = ["auth", "api", "db"]
 require-scope = true
 types = ["feat", "fix", "chore", "wip"]
+max-subject-length = 100
 ```
 
 ```toml
 # .commit-guard.toml
 enable = ["subject", "imperative"]
 ```
 
-CLI flags (`--enable`, `--disable`, `--scopes`, `--require-scope`, `--types`)
-take full precedence and ignore config file values when provided.
+CLI flags (`--enable`, `--disable`, `--scopes`, `--require-scope`, `--types`,
+`--max-subject-length`) take full precedence and ignore config file values when
+provided.
 
 ### Checking a range of commits
 

src/git_commit_guard/__init__.py

@@ -120,11 +120,12 @@ def _strip_comments(message):
     )
 
 
-def check_subject(
+def check_subject(  # noqa: PLR0913 Too many arguments in function definition (6 > 5)
     line,
     result,
     allowed_scopes=frozenset(),
     allowed_types=TYPES,
+    max_subject_length=MAX_SUBJECT_LEN,
     *,
     require_scope=False,
 ):
@@ -147,8 +148,8 @@ def check_subject(
         result.error("description must not start with uppercase")
     if desc.endswith("."):
         result.error("description must not end with period")
-    if len(line) > MAX_SUBJECT_LEN:
-        result.error(f"subject too long: {len(line)} > {MAX_SUBJECT_LEN}")
+    if len(line) > max_subject_length:
+        result.error(f"subject too long: {len(line)} > {max_subject_length}")
     return desc
 
 
@@ -231,6 +232,7 @@ class Args:
     allowed_scopes: frozenset
     require_scope: bool
     allowed_types: frozenset
+    max_subject_length: int
 
 
 def _resolve_enabled(args, config, parser):
@@ -249,6 +251,14 @@ def _resolve_enabled(args, config, parser):
     return enabled
 
 
+def _resolve_max_subject_length(args, config):
+    if args.max_subject_length is not None:
+        return args.max_subject_length
+    if "max-subject-length" in config:
+        return config["max-subject-length"]
+    return MAX_SUBJECT_LEN
+
+
 def _resolve_types(args, config):
     if args.types:
         return frozenset(t.strip() for t in args.types.split(","))
@@ -313,11 +323,19 @@ def _parse_args():
         metavar="TYPE[,TYPE,...]",
         help="allowed commit types (replaces defaults when set)",
     )
+    parser.add_argument(
+        "--max-subject-length",
+        type=int,
+        default=None,
+        metavar="N",
+        help=f"maximum subject line length (default: {MAX_SUBJECT_LEN})",
+    )
     args = parser.parse_args()
     config = _load_config()
     enabled = _resolve_enabled(args, config, parser)
     allowed_scopes, require_scope = _resolve_scopes(args, config)
     allowed_types = _resolve_types(args, config)
+    max_subject_length = _resolve_max_subject_length(args, config)
 
     if args.message_file:
         rev = None
@@ -339,6 +357,7 @@ def _parse_args():
         allowed_scopes=allowed_scopes,
         require_scope=require_scope,
         allowed_types=allowed_types,
+        max_subject_length=max_subject_length,
     )
 
 
@@ -368,6 +387,7 @@ def main():
             result,
             args.allowed_scopes,
             args.allowed_types,
+            args.max_subject_length,
             require_scope=args.require_scope,
         )
     if Check.IMPERATIVE in args.enabled:

tests/test_git_commit_guard.py

@@ -5,6 +5,7 @@
 import pytest
 
 from git_commit_guard import (
+    MAX_SUBJECT_LEN,
     TYPES,
     Result,
     _download_if_missing,
@@ -14,6 +15,7 @@
     _parse_checks,
     _parse_config_checks,
     _report,
+    _resolve_max_subject_length,
     _resolve_types,
     _strip_comments,
     check_body,
@@ -148,6 +150,16 @@ def test_empty_allowlist_accepts_any_scope(self):
         check_subject("fix(anything): add token", r, allowed_scopes=frozenset())
         assert r.ok
 
+    def test_custom_max_length_enforced(self):
+        r = Result()
+        check_subject("fix: add thing", r, max_subject_length=10)
+        assert not r.ok
+
+    def test_custom_max_length_passes(self):
+        r = Result()
+        check_subject("fix: ok", r, max_subject_length=10)
+        assert r.ok
+
     def test_custom_type_passes(self):
         r = Result()
         check_subject("wip: add thing", r, allowed_types=frozenset(["wip"]))
@@ -420,6 +432,28 @@ def test_invalid_check_name_exits(self):
             _parse_config_checks({"disable": ["bogus"]}, "disable")
 
 
+class TestResolveMaxSubjectLength:
+    def test_defaults_when_no_config_or_flag(self):
+        result = _resolve_max_subject_length(Namespace(max_subject_length=None), {})
+        assert result == MAX_SUBJECT_LEN
+
+    def test_cli_flag_overrides_default(self):
+        result = _resolve_max_subject_length(Namespace(max_subject_length=50), {})
+        assert result == 50  # noqa: PLR2004 Magic value used in comparison, consider replacing 50 with a constant variable
+
+    def test_config_overrides_default(self):
+        result = _resolve_max_subject_length(
+            Namespace(max_subject_length=None), {"max-subject-length": 60}
+        )
+        assert result == 60  # noqa: PLR2004 Magic value used in comparison, consider replacing 60 with a constant variable
+
+    def test_cli_overrides_config(self):
+        result = _resolve_max_subject_length(
+            Namespace(max_subject_length=50), {"max-subject-length": 60}
+        )
+        assert result == 50  # noqa: PLR2004 Magic value used in comparison, consider replacing 50 with a constant variable
+
+
 class TestResolveTypes:
     def test_defaults_when_no_config_or_flag(self):
         assert _resolve_types(Namespace(types=None), {}) == TYPES
@@ -713,6 +747,70 @@ def test_types_from_config(self, tmp_path):
         ):
             assert main() == 0
 
+    def test_max_subject_length_flag_passes(self, tmp_path):
+        f = tmp_path / "msg"
+        f.write_text("fix: ok\n\nbody\n\nSigned-off-by: A User <a@b.com>")
+        argv = [
+            "cg",
+            "--message-file",
+            str(f),
+            "--disable",
+            "signature",
+            "--max-subject-length",
+            "10",
+        ]
+        with patch("sys.argv", argv):
+            assert main() == 0
+
+    def test_max_subject_length_flag_fails(self, tmp_path):
+        f = tmp_path / "msg"
+        f.write_text(_VALID_MSG)
+        argv = [
+            "cg",
+            "--message-file",
+            str(f),
+            "--disable",
+            "signature",
+            "--max-subject-length",
+            "5",
+        ]
+        with patch("sys.argv", argv):
+            assert main() == 1
+
+    def test_max_subject_length_from_config(self, tmp_path):
+        f = tmp_path / "msg"
+        f.write_text(_VALID_MSG)
+        argv = ["cg", "--message-file", str(f), "--disable", "signature"]
+        with (
+            patch("sys.argv", argv),
+            patch(
+                "git_commit_guard._load_config",
+                return_value={"max-subject-length": 5},
+            ),
+        ):
+            assert main() == 1
+
+    def test_max_subject_length_cli_overrides_config(self, tmp_path):
+        f = tmp_path / "msg"
+        f.write_text(_VALID_MSG)
+        argv = [
+            "cg",
+            "--message-file",
+            str(f),
+            "--disable",
+            "signature",
+            "--max-subject-length",
+            "100",
+        ]
+        with (
+            patch("sys.argv", argv),
+            patch(
+                "git_commit_guard._load_config",
+                return_value={"max-subject-length": 5},
+            ),
+        ):
+            assert main() == 0
+
     def test_types_cli_overrides_config(self, tmp_path):
         f = tmp_path / "msg"
         f.write_text("wip: add thing\n\nbody\n\nSigned-off-by: A User <a@b.com>")