Fix enum member names conflicting with builtin type methods (#2660)

* Fix enum member name conflicts with built-in str methods by adding underscore suffixes

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

---------

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

Author: koxudaxi

src/datamodel_code_generator/reference.py

@@ -358,7 +358,92 @@ def _validate_field_name(cls, field_name: str) -> bool:
 
 
 class EnumFieldNameResolver(FieldNameResolver):
-    """Field name resolver for enum members with special handling for 'mro'."""
+    """Field name resolver for enum members with special handling for reserved names.
+
+    When using --use-subclass-enum, enums inherit from types like str or int.
+    Member names that conflict with methods of these types cause type checker errors.
+    This class detects and handles such conflicts by adding underscore suffixes.
+
+    The _BUILTIN_TYPE_ATTRIBUTES set is intentionally static (not using hasattr)
+    to avoid runtime Python version differences affecting code generation.
+    Based on Python 3.8-3.14 method names (union of all versions for safety).
+    Note: 'mro' is handled explicitly in get_valid_name for backward compatibility.
+    """
+
+    _BUILTIN_TYPE_ATTRIBUTES: ClassVar[frozenset[str]] = frozenset({
+        "as_integer_ratio",
+        "bit_count",
+        "bit_length",
+        "capitalize",
+        "casefold",
+        "center",
+        "conjugate",
+        "count",
+        "decode",
+        "denominator",
+        "encode",
+        "endswith",
+        "expandtabs",
+        "find",
+        "format",
+        "format_map",
+        "from_bytes",
+        "from_number",
+        "fromhex",
+        "hex",
+        "imag",
+        "index",
+        "isalnum",
+        "isalpha",
+        "isascii",
+        "isdecimal",
+        "isdigit",
+        "isidentifier",
+        "islower",
+        "isnumeric",
+        "isprintable",
+        "isspace",
+        "istitle",
+        "isupper",
+        "is_integer",
+        "join",
+        "ljust",
+        "lower",
+        "lstrip",
+        "maketrans",
+        "numerator",
+        "partition",
+        "real",
+        "removeprefix",
+        "removesuffix",
+        "replace",
+        "rfind",
+        "rindex",
+        "rjust",
+        "rpartition",
+        "rsplit",
+        "rstrip",
+        "split",
+        "splitlines",
+        "startswith",
+        "strip",
+        "swapcase",
+        "title",
+        "to_bytes",
+        "translate",
+        "upper",
+        "zfill",
+    })
+
+    @classmethod
+    def _validate_field_name(cls, field_name: str) -> bool:
+        """Check field name doesn't conflict with subclass enum base type attributes.
+
+        When using --use-subclass-enum, enums inherit from types like str or int.
+        Member names that conflict with methods of these types (e.g., 'count' for str)
+        cause type checker errors. This method detects such conflicts.
+        """
+        return field_name not in cls._BUILTIN_TYPE_ATTRIBUTES
 
     def get_valid_name(
         self,

tests/data/expected/main/openapi/enum_builtin_conflict.py

@@ -0,0 +1,14 @@
+# generated by datamodel-codegen:
+#   filename:  enum_builtin_conflict.yaml
+#   timestamp: 1985-10-26T08:21:00+00:00
+
+from __future__ import annotations
+
+from enum import Enum
+
+
+class StringMethodEnum(str, Enum):
+    count_ = 'count'
+    index_ = 'index'
+    format_ = 'format'
+    normal_value = 'normal_value'

tests/data/openapi/enum_builtin_conflict.yaml

@@ -0,0 +1,14 @@
+openapi: "3.0.0"
+info:
+  title: Test API
+  version: "1.0.0"
+paths: {}
+components:
+  schemas:
+    StringMethodEnum:
+      type: string
+      enum:
+        - count
+        - index
+        - format
+        - normal_value

tests/main/openapi/test_main_openapi.py

@@ -3569,3 +3569,16 @@ def test_main_openapi_x_enum_names(output_file: Path) -> None:
         assert_func=assert_file_content,
         expected_file="x_enum_names.py",
     )
+
+
+def test_main_enum_builtin_conflict(output_file: Path) -> None:
+    """Test enum member names that conflict with str methods get underscore suffix."""
+    with freeze_time(TIMESTAMP):
+        run_main_and_assert(
+            input_path=OPEN_API_DATA_PATH / "enum_builtin_conflict.yaml",
+            output_path=output_file,
+            input_file_type="openapi",
+            assert_func=assert_file_content,
+            expected_file="enum_builtin_conflict.py",
+            extra_args=["--use-subclass-enum"],
+        )