From 0af18c4172d5855547d54f2b09506a5cf8ac69ae Mon Sep 17 00:00:00 2001
From: Sydney Runkle <54324534+sydney-runkle@users.noreply.github.com>
Date: Mon, 7 Oct 2024 11:30:57 -0400
Subject: [PATCH] Add `invalid` schema placeholder (#1469)

---
 python/pydantic_core/core_schema.py | 22 ++++++++++++++++++++++
 src/validators/mod.rs               |  1 +
 tests/test_schema_functions.py      |  8 +++++++-
 3 files changed, 30 insertions(+), 1 deletion(-)

diff --git a/python/pydantic_core/core_schema.py b/python/pydantic_core/core_schema.py
index 922900170..b1c4c13b5 100644
--- a/python/pydantic_core/core_schema.py
+++ b/python/pydantic_core/core_schema.py
@@ -435,6 +435,26 @@ def model_ser_schema(cls: Type[Any], schema: CoreSchema) -> ModelSerSchema:
 ]
 
 
+class InvalidSchema(TypedDict, total=False):
+    type: Required[Literal['invalid']]
+    ref: str
+    metadata: Dict[str, Any]
+
+
+def invalid_schema(ref: str | None = None, metadata: Dict[str, Any] | None = None) -> InvalidSchema:
+    """
+    Returns an invalid schema, used to indicate that a schema is invalid.
+
+        Returns a schema that matches any value, e.g.:
+
+    Args:
+        ref: optional unique identifier of the schema, used to reference the schema in other places
+        metadata: Any other information you want to include with the schema, not used by pydantic-core
+    """
+
+    return _dict_not_none(type='invalid', ref=ref, metadata=metadata)
+
+
 class ComputedField(TypedDict, total=False):
     type: Required[Literal['computed-field']]
     property_name: Required[str]
@@ -3826,6 +3846,7 @@ def definition_reference_schema(
 # union which kills performance not just for pydantic, but even for code using pydantic
 if not MYPY:
     CoreSchema = Union[
+        InvalidSchema,
         AnySchema,
         NoneSchema,
         BoolSchema,
@@ -3882,6 +3903,7 @@ def definition_reference_schema(
 
 # to update this, call `pytest -k test_core_schema_type_literal` and copy the output
 CoreSchemaType = Literal[
+    'invalid',
     'any',
     'none',
     'bool',
diff --git a/src/validators/mod.rs b/src/validators/mod.rs
index 5f88d5dc8..fcd64ebf2 100644
--- a/src/validators/mod.rs
+++ b/src/validators/mod.rs
@@ -479,6 +479,7 @@ macro_rules! validator_match {
             $(
                 <$validator>::EXPECTED_TYPE => build_specific_validator::<$validator>($type, $dict, $config, $definitions),
             )+
+            "invalid" => return py_schema_err!("Cannot construct schema with `InvalidSchema` member."),
             _ => return py_schema_err!(r#"Unknown schema type: "{}""#, $type),
         }
     };
diff --git a/tests/test_schema_functions.py b/tests/test_schema_functions.py
index 6d96678c8..a15adfca5 100644
--- a/tests/test_schema_functions.py
+++ b/tests/test_schema_functions.py
@@ -291,6 +291,7 @@ def args(*args, **kwargs):
     (core_schema.decimal_schema, args(), {'type': 'decimal'}),
     (core_schema.decimal_schema, args(multiple_of=5, gt=1.2), {'type': 'decimal', 'multiple_of': 5, 'gt': 1.2}),
     (core_schema.complex_schema, args(), {'type': 'complex'}),
+    (core_schema.invalid_schema, args(), {'type': 'invalid'}),
 ]
 
 
@@ -299,7 +300,7 @@ def test_schema_functions(function, args_kwargs, expected_schema):
     args, kwargs = args_kwargs
     schema = function(*args, **kwargs)
     assert schema == expected_schema
-    if schema.get('type') in {None, 'definition-ref', 'typed-dict-field', 'model-field'}:
+    if schema.get('type') in {None, 'definition-ref', 'typed-dict-field', 'model-field', 'invalid'}:
         return
 
     v = SchemaValidator(schema)
@@ -354,3 +355,8 @@ def test_expected_serialization_types(return_schema):
             )
         )
     )
+
+
+def test_err_on_invalid() -> None:
+    with pytest.raises(SchemaError, match='Cannot construct schema with `InvalidSchema` member.'):
+        SchemaValidator(core_schema.invalid_schema())