[Docs]: Mention "rootDir" points to a different directory when using "projects"

[kettanaito]

Version

27.0.6

Steps to reproduce

Consider the following root-level configuration:

// jest.config.js
module.exports = {
  projects: ['<rootDir>/packages/*'],
  collectCoverageFrom: ['<rootDir>/src/*'}
}

Expected behavior

This needs to be mentioned in the documentation for projects. I've spent two days trying to understand why Jest doesn't pick up correct glob patterns in collectCoverageFrom just to find out that rootDir doesn't mean what I expect it to mean.

I've checked both projects and collectCoverageFrom sections of the documentation and found no mention whatsoever that would've helped me save time debugging.

Actual behavior

The values of rootDir in those two configuration options point to different paths:

• For projects the rootDir points to CWD, effectively.
• For collectCoverageFrom the rootDir points to each project's root directory.

This is confusing because the same placeholder is written in the same module but means different things.

Why this happens

This happens because when using projects Jest appends configurations like collectCoverageFrom to each individual project's configuration. In other words, the rootDir in collectCoverageFrom gets evaluated on each individual project's run, while the rootDir in projects is evaluated when the root-level config is parsed.

Additional context

No response

Environment

System:
    OS: macOS 12.1
    CPU: (8) arm64 Apple M1 Pro
  Binaries:
    Node: 16.13.2 - ~/.nvm/versions/node/v16.13.2/bin/node
    Yarn: 1.22.17 - /opt/homebrew/bin/yarn
    npm: 8.1.2 - ~/.nvm/versions/node/v16.13.2/bin/npm
  npmPackages:
    jest: ^27.0.6 => 27.3.1

[kettanaito]

A mention like this in the docs would be extremely helpful:

Note that when using projects, each option in the root-level configuration will be copied to each project's configuration upon test runs. This means that any <rootDir> values in the options will resolve to each project's root directory.

There's certainly a more straightforward explanation than this.

[SimenB]

PR very much welcome!

[kettanaito]

Hey, @SimenB. Awesome! I'll open a pull request as soon as I have a minute.

[github-actions]

This issue is stale because it has been open 30 days with no activity. Remove stale label or comment or this will be closed in 30 days.

[kettanaito]

I've opened a pull request that addresses this change to the documentation. Would appreciate a review!

[github-actions]

This issue is stale because it has been open 30 days with no activity. Remove stale label or comment or this will be closed in 30 days.

[github-actions]

This issue is stale because it has been open 30 days with no activity. Remove stale label or comment or this will be closed in 30 days.

[kettanaito]

The pull request is opened since a few months back: #12871
I'd appreciate some final review from the team to have it merged.

[github-actions]

This issue is stale because it has been open 30 days with no activity. Remove stale label or comment or this will be closed in 30 days.

[github-actions]

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