The typescript build is taking a long time to run so I used generateTrace from https://github.com/microsoft/TypeScript/pull/40063

It showed that most of the time I was comparing complicated classes with their subclasses. For example, one of the classes is the Objection base model (https://github.com/vincit/objection.js ), which is the base class that all my models inherit.

For example, I have code like:

 class User extends Model {} function doSomething(model: typeof Model) {} doSomething(User);

I have ~50 models. I think the first time TS finds each model it's slow, then it caches it. It takes approximately 5 seconds for TS to compare a specific model to the base Model . Model uses types from various libraries. Here is a screenshot of the trace, it takes 5 minutes to compare each model with Model :

Is there a way to make TS skip comparing Model with itself? That is, since the User extends the Model , there is no need to check the fields it inherited.

Edit:

I reduced the time to review all 50 models from 5min to 30s. I have a model map:

 type ModelType = 'user' | ... type ModelsMap = { user: User, ... }; getModel<T extends ModelType>(type: T): ModelsMap[T] {}

This is slow because ModelsMap[T] is a union of all models. It got faster if I return the base model when T is a union of all model types:

 type TypeToModel<T extends ModelType> = ModelType extends T ? Model : ModelsMap[T]; getModel<T extends ModelType>(type: T): TypeToModel<T> {}

However, it would be nice to know if there are any tricks to make the subclass comparison faster. For example, if it is possible to disable structural typing and use nominal for subclasses.