Make mypy ignore CoreSchema's typing (#528)

* Make mypy ignore CoreSchema's typing

* add comment

---------

Co-authored-by: Samuel Colvin <[email protected]>

Author: adriangb

pydantic_core/core_schema.py

@@ -3283,52 +3283,59 @@ def definition_reference_schema(
     return dict_not_none(type='definition-ref', schema_ref=schema_ref, metadata=metadata, serialization=serialization)
 
 
-CoreSchema = Union[
-    AnySchema,
-    NoneSchema,
-    BoolSchema,
-    IntSchema,
-    FloatSchema,
-    StringSchema,
-    BytesSchema,
-    DateSchema,
-    TimeSchema,
-    DatetimeSchema,
-    TimedeltaSchema,
-    LiteralSchema,
-    IsInstanceSchema,
-    IsSubclassSchema,
-    CallableSchema,
-    ListSchema,
-    TuplePositionalSchema,
-    TupleVariableSchema,
-    SetSchema,
-    FrozenSetSchema,
-    GeneratorSchema,
-    DictSchema,
-    AfterValidatorFunctionSchema,
-    BeforeValidatorFunctionSchema,
-    WrapValidatorFunctionSchema,
-    PlainValidatorFunctionSchema,
-    WithDefaultSchema,
-    NullableSchema,
-    UnionSchema,
-    TaggedUnionSchema,
-    ChainSchema,
-    LaxOrStrictSchema,
-    TypedDictSchema,
-    ModelSchema,
-    DataclassArgsSchema,
-    DataclassSchema,
-    ArgumentsSchema,
-    CallSchema,
-    CustomErrorSchema,
-    JsonSchema,
-    UrlSchema,
-    MultiHostUrlSchema,
-    DefinitionsSchema,
-    DefinitionReferenceSchema,
-]
+MYPY = False
+# See https://github.com/python/mypy/issues/14034 for details, in summary mypy is extremely slow to process this
+# union which kills performance not just for pydantic, but even for code using pydantic
+if not MYPY:
+    CoreSchema = Union[
+        AnySchema,
+        NoneSchema,
+        BoolSchema,
+        IntSchema,
+        FloatSchema,
+        StringSchema,
+        BytesSchema,
+        DateSchema,
+        TimeSchema,
+        DatetimeSchema,
+        TimedeltaSchema,
+        LiteralSchema,
+        IsInstanceSchema,
+        IsSubclassSchema,
+        CallableSchema,
+        ListSchema,
+        TuplePositionalSchema,
+        TupleVariableSchema,
+        SetSchema,
+        FrozenSetSchema,
+        GeneratorSchema,
+        DictSchema,
+        AfterValidatorFunctionSchema,
+        BeforeValidatorFunctionSchema,
+        WrapValidatorFunctionSchema,
+        PlainValidatorFunctionSchema,
+        WithDefaultSchema,
+        NullableSchema,
+        UnionSchema,
+        TaggedUnionSchema,
+        ChainSchema,
+        LaxOrStrictSchema,
+        TypedDictSchema,
+        ModelSchema,
+        DataclassArgsSchema,
+        DataclassSchema,
+        ArgumentsSchema,
+        CallSchema,
+        CustomErrorSchema,
+        JsonSchema,
+        UrlSchema,
+        MultiHostUrlSchema,
+        DefinitionsSchema,
+        DefinitionReferenceSchema,
+    ]
+elif False:
+    CoreSchema: TypeAlias = Dict[str, Any]
+
 
 # to update this, call `pytest -k test_core_schema_type_literal` and copy the output
 CoreSchemaType = Literal[