`proc_macro::SourceFile::path()` returns a non-public type

[mystor]

This function currently returns a syntax_pos::FileName, which is not exported from the proc_macro crate.

A good solution may be to export a struct FileName(syntax_pos::FileName) object which implements Display.

cc @jseyfried

[dtolnay]

Still a problem. proc_macro::SourceFile::path

[abonander]

Caused by d732da8

[inquisitivecrystal]

I believe that this was fixed by #52552.