Expose regex_engine flag

pydantic/_internal/_config.py

@@ -80,6 +80,7 @@ class ConfigWrapper:
     json_schema_serialization_defaults_required: bool
     json_schema_mode_override: Literal['validation', 'serialization', None]
     coerce_numbers_to_str: bool
+    regex_engine: Literal['rust-regex', 'python-re']
 
     def __init__(self, config: ConfigDict | dict[str, Any] | type[Any] | None, *, check: bool = True):
         if check:
@@ -248,6 +249,7 @@ def _context_manager() -> Iterator[None]:
     json_schema_serialization_defaults_required=False,
     json_schema_mode_override=None,
     coerce_numbers_to_str=False,
+    regex_engine='rust-regex',
 )
 
 

pydantic/config.py

@@ -787,5 +787,29 @@ class Model(BaseModel):
     ```
     """
 
+    regex_engine: Literal['rust-regex', 'python-re']
+    """
+    The regex engine to used for pattern validation
+
+    - `rust-regex` uses the [`regex`](https://docs.rs/regex) Rust crate,
+      which is non-backtracking and therefore more DDoS resistant, but does not support all regex features.
+    - `python-re` use the [`re`](https://docs.python.org/3/library/re.html) module,
+      which supports all regex features, but may be slower.
+
+    By default, the `rust-regex` engine will work.
+
+    ```py
+    from pydantic import BaseModel, ConfigDict, Field
+
+    class Model(BaseModel):
+        model_config = ConfigDict(regex_engine='python-re')
+
+        value: str = Field(pattern=r'^abc(?=def)')
+
+    print(Model(value='abcdef').value)
+    #> "abc"
+    ```
+    """
+
 
 __getattr__ = getattr_migration(__name__)