This patch fixed the unlink() issue for us.
However, the cache folder is never deleted and it contains a lot of files, so if you run drupal-check a lot, you should take care of clearing /tmp/ or you might run out of inodes.

Interesting. This sounds like it should also affect phpstan in general. I'll see how they generate the tmpDir. Because we should fix this upstream

So it doesn't handle it there either: https://github.com/phpstan/phpstan-src/blob/a1c7572a7be6251f2ef2265a97c75a26427f8741/src/Command/CommandHelper.php#L244

		if (!isset($tmpDir)) {
			$tmpDir = sys_get_temp_dir() . '/phpstan';
			$createDir($tmpDir);
		}

We should make sure to create a follow up there.

Sorry, I'm wrong. I realize this is about the custom configuration generated when running drupal-check and its clean up. Not the caches and such made by PHPStan

Thanks for having a look at this.

I agree that our CI is not isolated enough (and as a workaround we ended up having a cron job to clean the /tmp/phpstan_* folders).
We were just a bit surprised when we started running out of inodes after applying this patch because our /tmp/ folder was full of phpstan_15415/, phpstan_15890/, etc.

When using phpstan directly (or drupal-check without this patch), this is not a problem because the folder is always /tmp/phpstan/ and is reused by each run.
With this patch, the folder is different for every process so it does not make a lot of sense to keep it after the run because it will never be reused (unless another uses the same PID but it should not happen often).

To say the temp folder uses a lot of space is an understatement. I ran this twice on 2 different D8 and D9 sites and the result was below:

$ du -hs /tmp/phpstan/
939M    /tmp/phpstan/

Seriously? Rather than changing the folder name, would it make sense to create subdirectories with the pid instead? Something like /tmp/phpstan/123, /tmp/phpstan/234, etc. That way simply runningrm -rf /tmp/phpstan would clear everything out.

If you have these problems, use PHPStan directly and customize the tmpDir. I'm not going to rebuild features in PHPStan for this tool.

An easy workaround is to use the TMPDIR environment variable:

TMPDIR=./foo/ ./vendor/bin/drupal-check