But I'm wondering, what was the purpose of creating new instances, if every attribute was being passed in?

Apart fromfield_name_stack where a new instance is created. By the way, doesn't that break anything?

The purpose of creating new instances was to give the model a change to inject its custom core schema generator (some subclass ofGenerateSchema).

Refield_name_stack - I believe it continues to operate as expected.

In theory this can lead to inconsistent state, where in the process of generating a core schema for a field (and thus having one field name in the stack), we end up generating something else. However, the field names are only used when generating schema for*Validator classes, that can only be used when defining a field (meaning a new field name will be added to the stack, so it doesn't matter if the stack was reset or not).

Hmm. Interesting. Not sure I follow entirely - happy to take a closer look together and potentially refactor that structure.

For instance:

classSub(BaseModel):f:'Forward'Forward=intclassModel(BaseModel):sub:Sub

WhenSub is defined, schema generation fails becauseForward isn't defined. whenModel.sub is being defined, the field name stack is['sub']. We try to get the core schema ofSub but it needs to be rebuilt. Previous to your change, we would create a newGenerateSchema instance with an empty field name stack. But now, we build the core schema ofSub with the same instance. When we try to build the core schema ofSub.f, the field name stack is['sub', 'f'], so it is still valid. It can be inconsistent if we try to build somethingnot related to a field inSub (e.g. evaluating the type annotation of__pydantic_extra__, etc), but anyway the field name stack is only used by*Validator classes and such classes could only be used (in our example) in the context of fieldf, so the field name stack would be['sub', 'f'] so all good.

In theory this can lead to inconsistent state, where in the process of generating a core schema for a field (and thus having one field name in the stack), we end up generating something else. However, the field names are only used when generating schema for*Validator classes, that can only be used when defining a field (meaning a new field name will be added to the stack, so it doesn't matter if the stack was reset or not).