Jest runs out of memory when producing coverage for a large file

[sandersn]

🐛 Bug Report

Jest runs out of memory when producing coverage for a test file that is supposed to exercise the typescript compiler, which is 7.2 MB.

Background: I'm experimenting with switching Typescript to jest in order to get coverage-based testing. My first attempt is to create a small prototype that imitates our current tests in mocha. But it fails when I request a coverage report.

To Reproduce

Clone this repo: https://github.com/sandersn/jest-typescript-oomemory

1. npm install
2. npx jest --coverage

There are only two files that matter, though:

// @Filename: jest.config.js
module.exports = {}

// @Filename: x.test.js
var ts = require('./typescript.js')

Expected behavior

A coverage report. In my original code, I wanted to see how well Typescript's tests covered the typescript compiler.

Link to repl or repo (highly encouraged)

https://github.com/sandersn/jest-typescript-oomemory

Run npx envinfo --preset jest

Paste the results here:

✔ jest-typescript-oomemory  [master|…1]$ npx envinfo --preset jest
npx: installed 1 in 0.725s

  System:
    OS: Linux 4.15 Ubuntu 18.04.2 LTS (Bionic Beaver)
    CPU: (8) x64 Intel(R) Core(TM) i7-6700 CPU @ 3.40GHz
  Binaries:
    Node: 11.14.0 - ~/.nvm/versions/node/v11.14.0/bin/node
    Yarn: 1.16.0 - ~/.nvm/versions/node/v11.14.0/bin/yarn
    npm: 6.7.0 - ~/.nvm/versions/node/v11.14.0/bin/npm
  npmPackages:
    jest: ^24.8.0 => 24.8.0 

[thymikee]

We use Istanbul to generate coverege, which works as a Babel plugin so I suppose it's mostly because of that. Not sure how much we can do currently to mitigate that.

But, there's an open issue on migrating our coverage system to built-in V8 coverage: #7062 which should speed it up significantly.

We'd love some help in the area. cc @bcoe

[SimenB]

Could we maybe write coverage data to disk as we go to free up memory, and load it back up when we're done running tests to write the reports?

EDIT: Oh, it's one gigantic file. hmmm

EDIT2: And I see now running it that it fails in @babel/traverse and not from keeping actual coverage in memory, so using v8 coverage could indeed help

[SimenB]

I'm getting somewhere with v8 coverage, btw. Horribly, horribly hacky, but a sneak peak:

(this is just requiring the file, like in your reproduction)

[SimenB]

@sandersn v8 coverage is out with jest 25, would love it if you could give it a whirl

[github-actions]

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