Reverting problematic fix from 2.6 release, fixing schema building bug (

#8718)

pydantic/_internal/_generate_schema.py

@@ -438,8 +438,6 @@ def clean_schema(self, schema: CoreSchema) -> CoreSchema:
         if collect_invalid_schemas(schema):
             raise self.CollectedInvalid()
         schema = validate_core_schema(schema)
-        if 'definitions' in schema:
-            schema['definitions'] = list(reversed(schema['definitions']))
         return schema
 
     def collect_definitions(self, schema: CoreSchema) -> CoreSchema:

tests/test_discriminated_union.py

@@ -1700,6 +1700,7 @@ class DiscriminatedModel(BaseModel):
         assert exc_info.code == 'callable-discriminator-no-tag'
 
 
+@pytest.mark.xfail(reason='Issue not yet fixed, see: https://github.com/pydantic/pydantic/issues/8271.')
 def test_presence_of_discriminator_when_generating_type_adaptor_json_schema_definitions() -> None:
     class ItemType(str, Enum):
         ITEM1 = 'item1'

tests/test_json_schema.py

@@ -5879,3 +5879,31 @@ class Model(BaseModel):
         x: BaseModel
 
     assert 'description' not in Model.model_json_schema()['$defs']['BaseModel']
+
+
+def test_recursive_json_schema_build() -> None:
+    """
+    Schema build for this case is a bit complicated due to the recursive nature of the models.
+    This was reported as broken in https://github.com/pydantic/pydantic/issues/8689, which was
+    originally caused by the change made in https://github.com/pydantic/pydantic/pull/8583, which has
+    since been reverted.
+    """
+
+    class AllowedValues(str, Enum):
+        VAL1 = 'Val1'
+        VAL2 = 'Val2'
+
+    class ModelA(BaseModel):
+        modelA_1: AllowedValues = Field(..., max_length=60)
+
+    class ModelB(ModelA):
+        modelB_1: typing.List[ModelA]
+
+    class ModelC(BaseModel):
+        modelC_1: ModelB
+
+    class Model(BaseModel):
+        b: ModelB
+        c: ModelC
+
+    assert Model.model_json_schema()