fix(openapi): preserve acronyms in generated exception descriptions (#4921)

* fix(openapi): preserve acronyms in generated exception descriptions

The pascal_case_to_text helper split before every capital letter, so
exception names containing acronyms produced unreadable schema
descriptions, e.g. InvalidAPIKeyError became "Invalid A P I Key Error".

Split only where a lowercase letter or digit meets an uppercase letter,
or where an uppercase run is followed by a new word, so consecutive
capitals stay together and the same name now renders as
"Invalid API Key Error".

Fixes #4004

* refactor(openapi): convert word boundary pattern to a verbose regex

Author: Bishwas-py

litestar/_openapi/responses.py

@@ -42,12 +42,19 @@
 
 __all__ = ("create_responses_for_handler",)
 
-CAPITAL_LETTERS_PATTERN = re.compile(r"(?=[A-Z])")
+WORD_BOUNDARY_PATTERN = re.compile(
+    r"""
+    (?<=[a-z0-9])(?=[A-Z])      # a lowercase letter or digit, followed by an uppercase letter
+    |
+    (?<=[A-Z])(?=[A-Z][a-z])    # an uppercase run, followed by a new capitalized word
+    """,
+    re.VERBOSE,
+)
 
 
 def pascal_case_to_text(string: str) -> str:
     """Given a 'PascalCased' string, return its split form- 'Pascal Cased'."""
-    return " ".join(re.split(CAPITAL_LETTERS_PATTERN, string)).strip()
+    return " ".join(re.split(WORD_BOUNDARY_PATTERN, string)).strip()
 
 
 def create_cookie_schema(cookie: Cookie) -> Schema:

tests/unit/test_openapi/test_responses.py

@@ -15,6 +15,7 @@
 from litestar._openapi.responses import (
     ResponseFactory,
     create_error_responses,
+    pascal_case_to_text,
 )
 from litestar._openapi.schema_generation.plugins import openapi_schema_plugins
 from litestar.datastructures import Cookie, ResponseHeader
@@ -151,6 +152,37 @@ class AlternativePetException(HTTPException):
         assert schema.type
 
 
+@pytest.mark.parametrize(
+    ("string", "expected"),
+    [
+        ("PetException", "Pet Exception"),
+        ("InvalidAPIKeyError", "Invalid API Key Error"),
+        ("HTTPException", "HTTP Exception"),
+        ("ValidationException", "Validation Exception"),
+        ("API", "API"),
+        ("Error", "Error"),
+        ("error", "error"),
+        ("HTTP404Error", "HTTP404 Error"),
+        ("Base64Decoder", "Base64 Decoder"),
+        ("", ""),
+    ],
+)
+def test_pascal_case_to_text(string: str, expected: str) -> None:
+    assert pascal_case_to_text(string) == expected
+
+
+def test_create_error_responses_preserves_acronyms_in_description() -> None:
+    class InvalidAPIKeyError(HTTPException):
+        status_code = 401
+
+    _, response = next(create_error_responses(exceptions=[InvalidAPIKeyError]))
+
+    assert response.content
+    schema = response.content[MediaType.JSON].schema
+    assert isinstance(schema, Schema)
+    assert schema.description == "Invalid API Key Error"
+
+
 def test_create_error_responses_with_non_http_status_code() -> None:
     class HouseNotFoundError(HTTPException):
         status_code: int = 420