Fix crash when regex option raises a re.error exception.

Closes pylint-dev#7202

doc/whatsnew/fragments/7202.bugfix

@@ -0,0 +1,3 @@
+Fix crash when regex option raises a `re.error` exception.
+
+Closes #7202

pylint/config/argument.py

@@ -99,6 +99,18 @@ def _py_version_transformer(value: str) -> tuple[int, ...]:
     return version
 
 
+def _regex_transformer(value: str) -> Pattern[str]:
+    """Return `re.compile(value)`."""
+    try:
+        return re.compile(value)
+    except re.error as e:
+        msg = (
+            f"\nProvided regular expression: {e.pattern}\n"
+            f"Error beginning at index {e.pos}: {e.msg}"
+        )
+        raise argparse.ArgumentTypeError(msg)
+
+
 def _regexp_csv_transfomer(value: str) -> Sequence[Pattern[str]]:
     """Transforms a comma separated list of regular expressions."""
     patterns: list[Pattern[str]] = []
@@ -130,7 +142,7 @@ def _regexp_paths_csv_transfomer(value: str) -> Sequence[Pattern[str]]:
     "non_empty_string": _non_empty_string_transformer,
     "path": _path_transformer,
     "py_version": _py_version_transformer,
-    "regexp": re.compile,
+    "regexp": _regex_transformer,
     "regexp_csv": _regexp_csv_transfomer,
     "regexp_paths_csv": _regexp_paths_csv_transfomer,
     "string": pylint_utils._unquote,

tests/config/test_config.py

@@ -111,6 +111,20 @@ def test_unknown_py_version(capsys: CaptureFixture) -> None:
     assert "the-newest has an invalid format, should be a version string." in output.err
 
 
+def test_regex_error(capsys: CaptureFixture) -> None:
+    """Check that we correctly error when an an option is passed whose value is an invalid regular expression."""
+    with pytest.raises(SystemExit):
+        Run(
+            [str(EMPTY_MODULE), r"--function-rgx=[\p{Han}a-z_][\p{Han}a-z0-9_]{2,30}$"],
+            exit=False,
+        )
+    output = capsys.readouterr()
+    assert (
+        "Provided regular expression: [\\p{Han}a-z_][\\p{Han}a-z0-9_]{2,30}$\nError beginning at index 1: bad escape \\p"
+        in output.err
+    )
+
+
 def test_short_verbose(capsys: CaptureFixture) -> None:
     """Check that we correctly handle the -v flag."""
     Run([str(EMPTY_MODULE), "-v"], exit=False)