perf: remove ts resolved module cache file

[jsaguet]

Summary

I noticed that running ts-jest was very slow in one of my projects so I dig a little into why and noticed the performance bottleneck comes from the getCacheKey function and in particular the writeFileSync that is being called to store the dependency graph.

Writing this file is what's taking most of the time in this process as the content we write is very heavy : the whole file content and its resolved module names.

I ran a few tests on a project with different configurations and here are the result:

Case	1st run (clean jest cache)	2nd run (with jest cache)
Current ts-jest (Writing dependency graph file)	218s	16s
No cache (--no-cache)	44s	44s
This PR version (No dependency graph file)	47s	14s

As we can see from the results, the fastest way to run ts-jest is by disabling jest cache (--no-cache) but we can get pretty close to that timing when we skip writing the dep graph file.

What's even more interesting is that on subsequent runs, even reading the dep graph file is less performant than recomputing the graph (2s less in this case)

So I'm opening this PR to completely remove the dependency graph file as it seems to only slow down the process without any gain. It should largely improve ts-jest performance when not using isolated modules.

Fixes #2696

Test plan

Does this PR introduce a breaking change?

• Yes
• No

Other information

[ahnpnl]

In the past, we introduced that checking dep graph and includes related files into cache key because we had the issue in watch mode.

You can check #2436 for more information.

Reverting that PR is fine, it will solve problems for some users but introduce past problems for other users.

I haven’t found a way how to do type checking probably either. Apparently doing type checking inside Jest transformer is very poor performant. If we can somehow do it from top level before Jest runs, it would be ideal.

[jsaguet-betclic]

The dep grah itself and how it's computed is not removed or changed with this PR.
It will just be recomputed every time the cache key is computed.

The only change is that it will not be stored on the file system between runs because that's the part that slows ts-jest a lot.

Re-computing it is a lot faster

[ahnpnl]

Ah I see, lgtm

[ahnpnl]

Something is already wrong with the tests on main, we can merge this since it’s not related.

[decline]

Just wanted to leave a big THANK YOU for this fix! We have a very large codebase where we couldn't even run all tests at once anymore, without setting isolatedModules: true because of the long run times. Now everything is super fast and we can have type-safety again by removing the isolatedModules setting. Really happy 🎉