feat(core): add support for pnpm as package manager

[AbdelHajou]

stryker init command now has the option to use pnpm instead of npm as package manager.

Resolves #3448 and closes #3221 (duplicates)

[nicojs]

Thanks for the PR! Looks good, also with the additional test 🧡

There is one big showstopper left. We need to explicitly specify plugins here, since the automatic plugin detection fails with pnpm's installation model.

So when the @stryker-mutator/jest-runner gets installed, it should also be added to the plugins array in the stryker.conf.json file. Would you feel comfortable to add that as well?

Actually, this should also be added to troubleshooting.md.

[AbdelHajou]

Thanks for the review @nicojs , I'm working on it. Is it true that during stryker init it's unknown whether the project uses TypeScript, so it can't be added to the plugins array automatically? I guess this is where the Troubleshooting docs will come in handy.

[nicojs]

Thanks a lot, @AbdelHajou. This looks great! You even documented the issue in troubleshooting.md 👍

I've got a remark on the troubleshooting. You can reproduce the issue using these repro steps:

npm i -g pnpm
mkdir tmp && cd tmp
pnpm init --yes
pnpm add -D mocha @stryker-mutator/core @stryker-mutator/mocha-runner
mkdir src
mkdir test
touch src/math.js
# export function add(a, b) {
#  return a + b;
# }

touch test/math.spec.js
# import { add } from '../src/math.js';
# import assert from 'node:assert/strict';
# 
# describe('add', () => {
#    it('should return 42 for 42 and 0', () => {
#        assert.equal(add(42, 0), 42);
#    });
# });

code package.json
# Add "type": "module"
npx mocha

#  add
#    ✔ should return 42 for 42 and 0

touch stryker.conf.json
# {
#     "$schema": "./node_modules/@stryker-mutator/core/schema/stryker-schema.json",
#     "testRunner": "mocha"
# }
npx stryker

# see the error

[nicojs]

The problem isn't that mutation testing takes too long; the problem is this when running Stryker:

Error: Could not inject [class ChildProcessTestRunnerWorker]. Cause: Cannot find TestRunner plugin "mocha". No TestRunner plugins were loaded.

The @stryker-mutator/typescript-checker doesn't improve performance; it dramatically decreases it, in favor of mutation report quality. I wouldn't name typescript at all for this issue.

[AbdelHajou]

Thank you, I've updated the docs. I still mention typescript (in the form of typescript-checker) because this should be the only plugin causing trouble for newer projects. The others should be added by stryker init. If you have any more feedback I'll be happy to process it during the hackathon tomorrow! 🤠