[Bug]: [mutate] Windows: @pest-mutate-ignore comments land on line 1 in files with LF line endings

What Happened

On Windows, // @pest-mutate-ignore comments don't apply in files with LF line endings, which is what a .gitattributes with eol=lf produces. The mutants they should suppress are still generated and reported.

MutationGenerator::generate() locates the comments by splitting the source on PHP_EOL:

foreach (explode(PHP_EOL, $contents) as $lineNumber => $line) {

On Windows PHP_EOL is "\r\n", so an LF file isn't split at all. The whole file becomes line 1, and every ignore comment is recorded for line 1 instead of its own line.

Expected: ignore comments apply to their own line, whatever the file's line endings or the OS.

How to Reproduce

On Windows, take any LF file with a // @pest-mutate-ignore comment on a line that has a surviving mutant, and run pest --mutate.

This is currently hidden by #1927, which makes every mutant count as killed on Windows anyway. With that one patched locally (quotes removed from --filter), the sample repository's composer test:mutate on Windows reports the 2 mutants on the two lines of src/Tty.php marked // @pest-mutate-ignore: RemoveArrayItem as untested (94.87%). Replacing PHP_EOL with "\n" in that explode() as well gives 100%, the same as on Linux.

Suggested fix: preg_split('/\R/', $contents), which handles LF and CRLF files on any OS.

Sample Repository

https://github.com/Shoxcie/composer-tty

Pest Version

5.2.1 (pestphp/pest-plugin-mutate v5.0.2)

PHP Version

8.5.10

Operation System

Windows

Notes

Filed here because issues are disabled on pestphp/pest-plugin-mutate. Related Windows issues: #1927, #1916, #1313.

Start at MutationGenerator::generate(), where ignore comments are split from the source using PHP_EOL. Reproduce the issue with an LF-ended file on Windows, then run the sample repository's composer test:mutate command; done means ignore comments apply to their own lines for both LF and CRLF files.