Prevent Typescript compiler from checking entire classes to save time?

Question

Typescript compilation 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 was comparing complicated classes with their subclasses. E.g. one of the classes is the base Objection model (https://github.com/vincit/objection.js), which is the base class that all my models inherit.

E.g. 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 encounters each model is slow, then it caches it. It takes about 5s for TS to compare a specific model with the base Model. Model uses types from several libraries. Here's a screenshot of the trace, it takes 5min just to compare each model with Model:

Is there a way to get TS to skip comparing Model with itself? I.e. since User extends Model, there's no need to check the fields it inherited.

Edit:

I reduced the time to check the 50 models from 5min to 30s. I have a map of models:

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 the models. It became faster if I return the base model when T is an union of all the model types:

type TypeToModel<T extends ModelType> = ModelType extends T ? Model : ModelsMap[T];

getModel<T extends ModelType>(type: T): TypeToModel<T> {}

However, it would still be nice to know if there are hacks to make comparing subclass faster. E.g. if it's possible to disable structural typing and use nominal for subclasses.

Reginaldreginauld

Could you please provide more information how you measure it? I did not know that it is possible to debug ts in chrome. Thank you – Turk

The author of generateTrace has instructions here: github.com/microsoft/TypeScript/pull/… The trace shows that each comparison between the base model class and a subclass takes a few seconds. – Reginaldreginauld

I imagine you've already taken a look at the compiler API, but if not, then this is a great time. You could use incremental compilation and cache AST outputs (e.g. according to a digest of each module's contents). I don't know if a project like that already exists, but I can't be the first one to imagine wanting to cache compilation results. – Katinka

For others coming across this question, Typescript performance has generally been causing issues for Objection since at least TS 4.4, worsening with 4.5. 1 2 3. Since this issue has to do with the internal typings of Objection (other ORMs and libraries aren't having this problem) I recommend opening an issue. – Availability

I would like to know how you traced this process. – Pipsqueak

Answer 1

I'm not sure it will be very helpful in your case, but you can dramatically speed up the process by allowing the incremental flag to your tsc command:

// package.json
"tsc": "tsc -v && tsc --noEmit --skipLibCheck --incremental",

This will create a tsconfig.tsbuildinfo file, that is actually a graph of your codebase. Typescript will then only compare the entries you have changed. The first compilation will be slow, because it will generate the graph, but afterwards, the compilation time will be cut by 3 at least.

Anywise

Answer 2

Some tsc flags that can help with typescript compilation speed are skipLibCheck and incremental

If that is still not fast enough, consider using a different compiler than tsc (at least in-dev). Some examples of what you could use:

• ts-node-dev
• ts-node
• swc

Decline