[core] Allow XPath rules to access the current file name

[oowekyala]

Discussed in #3444

^{Originally posted by rsoesemann August 6, 2021}
I want to use XPath rules to check whether files name comply with certain naming rules? Is that possible in PMD?

-> not currently supported, we can add an attribute to apex root nodes in PMD 6. In PMD 7 we can add an attribute to all RootNodes

[rsoesemann]

@oowekyala would it be hard to make that work for arbitrary languages or at least XML? I need it for the hundreds of different XML metadata files that exist in the Salesforce ecosystem.

[oowekyala]

For xml ideally we'd use an xpath function, since we wouldn't want to add attributes that don't exist... I'll look into whether that's possible, if so, maybe we can make that language-independent