Fix breaking change in to_snake from v2.7 -> v2.8 (#9812)

Author: sydney-runkle

pydantic/alias_generators.py

@@ -49,13 +49,14 @@ def to_snake(camel: str) -> str:
     Returns:
         The converted string in snake_case.
     """
-    # `(?<=[a-zA-Z])(?=[0-9])` matches the space between a letter and a digit
-    # `(?<=[a-z0-9])(?=[A-Z])` matches the space between a lowercase letter / digit and uppercase letter
-    # `(?<=[A-Z])(?=[A-Z][a-z])` matches the space between two uppercase letters when the latter is followed by a lowercase letter
-    # `-` matches a hyphen in order to convert kebab case strings
-    snake = re.sub(
-        r'(?<=[a-zA-Z])(?=[0-9])|(?<=[a-z0-9])(?=[A-Z])|(?<=[A-Z])(?=[A-Z][a-z])|-',
-        '_',
-        camel,
-    )
+    # Handle the sequence of uppercase letters followed by a lowercase letter
+    snake = re.sub(r'([A-Z]+)([A-Z][a-z])', lambda m: f'{m.group(1)}_{m.group(2)}', camel)
+    # Insert an underscore between a lowercase letter and an uppercase letter
+    snake = re.sub(r'([a-z])([A-Z])', lambda m: f'{m.group(1)}_{m.group(2)}', snake)
+    # Insert an underscore between a digit and an uppercase letter
+    snake = re.sub(r'([0-9])([A-Z])', lambda m: f'{m.group(1)}_{m.group(2)}', snake)
+    # Insert an underscore between a lowercase letter and a digit
+    snake = re.sub(r'([a-z])([0-9])', lambda m: f'{m.group(1)}_{m.group(2)}', snake)
+    # Replace hyphens with underscores to handle kebab-case
+    snake = snake.replace('-', '_')
     return snake.lower()

pyproject.toml

@@ -246,3 +246,10 @@ skip = '.git,env*,pydantic/v1/*'
 # `ser` - abbreviation for "ser"ialisation
 # `crate` - a rust crate
 ignore-words-list = 'gir,ser,crate'
+
+[tool.codeflash]
+module-root = "pydantic"
+tests-root = "tests"
+test-framework = "pytest"
+ignore-paths = []
+formatter-cmd = ["ruff check --exit-zero --fix $file", "ruff format $file"]

tests/test_utils.py

@@ -542,6 +542,7 @@ def test_snake2pascal(value: str, result: str) -> None:
         ('Kebab-Snake', 'kebab_snake'),
         ('PascalToSnake', 'pascal_to_snake'),
         ('snake_to_snake', 'snake_to_snake'),
+        ('snakeV2', 'snake_v2'),
     ],
 )
 def test_to_snake(value: str, result: str) -> None: