Cache keys are hashed absolute paths, so the cache can never be reused across checkouts (CI → local, git worktrees)

[webard]

Subject	Details
Rector version	2.6.6
Installed as	composer dependency

ChangedFilesDetector keys every cache entry on the absolute path of the file:

private function getFilePathCacheKey(string $filePath): string
{
    return $this->fileHasher->hash($this->resolvePath($filePath) . $this->scopeSuffix);
}

private function resolvePath(string $filePath): string
{
    $realPath = realpath($filePath);
    // ...
    return $realPath;
}

The path is hashed into the cache file's name, so the cache is bound to one location on disk. Move the project - a second git worktree, a CI checkout, a container mount - and the cache is 100% misses while containing nothing that could be rewritten to fix it.

Measurements

A 12 762-file project, 14 cores, PHP 8.5.10.

Scenario	Wall time
fresh checkout, empty cache	224 s
same checkout, warm cache	5 s
fresh checkout, cache copied from another checkout of the same commit	247 s (291 MB copied for nothing)

For comparison, the same experiment with the other two tools in the same toolchain, copying their caches into the same fresh checkout:

Tool	cold	seeded from another checkout
Pint (PHP-CS-Fixer)	105 s	2.7 s
PHPStan	43 s	4.4 s
Rector	224 s	247 s

Rector's cache records nothing about the environment. Grepping all 12 761 entries of a populated tmp/rector finds zero references to a PHP version, an extension list or an OS - each entry is just a content hash. The absolute path is the only thing standing between that cache and reuse somewhere else.

Proposal

Key on the path relative to the project root and re-absolutize on read, as PHPStan does.
Two honest caveats:

1. Existing caches invalidate once on upgrade.
2. Files outside the project root (if any can reach the detector) need a defined behaviour - PHPStan's transformer leaves an already-absolute path untouched, which also keeps old-format caches readable.

I am happy to send a PR if you agree with the direction. I would rather hear which shape you want (anchor directory as a constructor dependency vs resolving it from the config) than guess and have it rewritten.

[TomasVotruba]

Thanks for the proposal 👍 I'd like to see numbers for your idea :)

Can you send PR so we can test it out?