Not sure if we need this feature. But in this case I'd prefer a new parameter instead of a new resource type.

I'm not sure about adding a parameter.

The current behavior is to check that the file still exists before evaluating freshness and returnfalse if it doesn't. So it already detects when a file is removed, despite being more of a side-effect than something truly desired, I guess. A parameter would toggle the detection of the file creation, but would have no effect on the detection of its removal because we can't evaluate freshness against a missing file anyway.

Or maybeFileResource should throw an exception (or deprecation notice to keep BC) when the file is removed and said parameter does not allow it, but I'm not sure such strictness would make sense.

Maybe aCombined[File]Resource (or a better name) where you can add multiple[File]Resources and check until one gives false.

Combined[File]Resource([newFileExistenceResource('phpunit.xml'),newFileResource('phpunit.xml')]);

That would still require changes toFileResource as it currently throws an exception if the file does not exist.

Furthermore, having such resource class to combine other resources would be superfluous: the container is recompiled as soon as at least one of its resources is updated, we can simply add both resources from your example to the container directly.

Closing in favor of#21408 which wraps the required logic and should be the way to go now.
Thanks for the PR.