fix: catch re.error in re.Pattern compilation to raise ValidationError instead

apischema/std_types.py

@@ -24,7 +24,7 @@
 from typing import Deque, List, TypeVar
 from uuid import UUID
 
-from apischema import deserializer, schema, serializer, type_name
+from apischema import ValidationError, deserializer, schema, serializer, type_name
 from apischema.conversions import Conversion, as_str, catch_value_error
 
 T = TypeVar("T")
@@ -88,10 +88,17 @@ def to_base64(b: bytes) -> str:
 
 # =================== pattern ===================
 
-Pattern = type(re.compile(r""))
-deserializer(Conversion(catch_value_error(re.compile), source=str, target=Pattern))
-serializer(Conversion(operator.attrgetter("pattern"), source=Pattern, target=str))
-type_name(None)(Pattern)
+
+@deserializer
+def _compile(pattern: str) -> re.Pattern:
+    try:
+        return re.compile(pattern)
+    except re.error as err:
+        raise ValidationError(str(err))
+
+
+serializer(Conversion(operator.attrgetter("pattern"), source=re.Pattern, target=str))
+type_name(None)(re.Pattern)
 
 # ==================== uuid =====================
 

tests/integration/test_pattern_deserialization.py

@@ -0,0 +1,16 @@
+import re
+
+import pytest
+
+from apischema import ValidationError, deserialize
+
+
+def test_valid_pattern():
+    pattern = deserialize(re.Pattern, "(a|b)")
+    assert isinstance(pattern, re.Pattern)
+    assert pattern.pattern == "(a|b)"
+
+
+def test_invalid_pattern():
+    with pytest.raises(ValidationError):
+        deserialize(re.Pattern, "(a")