bug#50733: 28.0.1; project-find-regexp can block Emacs for a long time

[Juri Linkov]

>> Is its command line more complex than etags?
>
> No, it's much more simple.  Assuming you are in the top-level
> directory of the Emacs source tree, the command is just:
>
>      mkid
>
> That produces a file named 'ID' in that directory.

I tried to generate 'ID' with 'mkid', and then xref-find-references
works fine with it.  The only problem is that it finds occurrences
in .elc files.