Fix --base-class-map and --enum-field-as-literal-map long inline json support (#3075)

* Create test

* Fix base-class-map and enum-field-as-literal-map long inline json support

* Improve explanatory comment

* Create test

* Fix formatting

---------

Co-authored-by: Antonio Spadaro <9268789+ilovelinux@users.noreply.github.com>
Co-authored-by: Koudai Aono <koxudaxi@gmail.com>

Author: ilovelinux

src/datamodel_code_generator/arguments.py

@@ -88,14 +88,26 @@ def _external_ref_mapping(value: str) -> str:
 def _json_value_or_file(value: str) -> dict[str, object]:
     """Parse a JSON value or load it from a JSON file path."""
     path = Path(value).expanduser()
-    if path.is_file():
+
+    # In Python<=3.13, long json values would cause `path.is_file()` to raise an OSError exception
+    # because the string is too long to be interpreted as a filename.
+    # This changed in Python>=3.14 since now `path.is_file()` catches OSError and returns `false` instead.
+    # Therefore we are going to catch OSError exception raised in Python<=3.13 to replicate Python>=3.14 behavior.
+    is_file: bool
+    try:
+        is_file = path.is_file()
+    except OSError:
+        is_file = False
+
+    if is_file:
         try:
             json_input = path.read_text(encoding=DEFAULT_ENCODING)
         except (OSError, UnicodeDecodeError) as e:
             msg = f"Unable to read JSON file {value!r}: {e}"
             raise ArgumentTypeError(msg) from e
     else:
         json_input = value
+
     try:
         result = json.loads(json_input)
     except json.JSONDecodeError as e:

tests/main/jsonschema/test_main_jsonschema.py

@@ -2,6 +2,7 @@
 
 from __future__ import annotations
 
+import itertools
 import json
 import os
 import tempfile
@@ -3143,6 +3144,21 @@ def test_main_jsonschema_base_class_map_empty_list(output_file: Path) -> None:
     )
 
 
+def test_main_jsonschema_base_class_map_long_json(output_file: Path) -> None:
+    """Test base_class_map with very long json string."""
+    run_main_and_assert(
+        input_path=JSON_SCHEMA_DATA_PATH / "base_class_map_empty_list.json",
+        output_path=output_file,
+        input_file_type="jsonschema",
+        assert_func=assert_file_content,
+        expected_file="base_class_map_empty_list.py",
+        extra_args=[
+            "--base-class-map",
+            '{"User": [' + ",".join(itertools.repeat('""', 100)) + "]}",
+        ],
+    )
+
+
 def test_long_description(output_file: Path) -> None:
     """Test long description handling."""
     run_main_and_assert(
@@ -4659,6 +4675,22 @@ def test_main_enum_field_as_literal_map_from_file(output_file: Path, tmp_path: P
     )
 
 
+def test_main_enum_field_as_literal_map_long_json(output_file: Path) -> None:
+    """Test enum_field_as_literal_map with very long json string."""
+    long_inline_mapping = '{"status": "literal",' + ",".join(f'"unused_field_{i}": "enum"' for i in range(100)) + "}"
+    run_main_and_assert(
+        input_path=JSON_SCHEMA_DATA_PATH / "enum_field_as_literal_map.json",
+        output_path=output_file,
+        input_file_type=None,
+        assert_func=assert_file_content,
+        expected_file="enum_field_as_literal_map.py",
+        extra_args=[
+            "--enum-field-as-literal-map",
+            long_inline_mapping,
+        ],
+    )
+
+
 def test_main_enum_field_as_literal_map_override_global(output_file: Path) -> None:
     """Test --enum-field-as-literal-map overrides global --enum-field-as-literal."""
     run_main_and_assert(