On 12/10/23 11:28, Stefan Monnier via Bug reports for GNU Emacs, the 
Swiss army knife of text editors wrote:
 >> +(defun etags--ensure-file (file)
 >> +  "Ensure FILE can be visited.
 >> +
 >> +FILE should be an expanded file name.
 >> +This function tries to locate FILE, possibly adding it a suffix
 >> +present in `tags-compression-info-list'.  If the file can't be found,
 >> +signals an error.
 >> +Else, returns the filename that can be visited for sure."
 >> +  (let ((f (locate-file file nil tags-compression-info-list)))
 >> +    (unless f
 >> +      (signal 'file-missing (list "Cannot locate file in TAGS" file)))
 >> +    f))
 >
 > The patch looks pretty good, but other parts of the code use
 > check `auto-compression-mode` before using `tags-compression-info-list`,
 > so we should probably do the same here.

Thank you!  Yes, I should've added that check.  I attach a patch that
incorporates the check.

 > As other comments mention in the file, this arrangement is suboptimal
 > because the search for compressed filenames should probably be moved to
 > jka-compr's code (e.g. using `jka-compr-compression-info-list` rather
 > than `tags-compression-info-list`).

Yes, but I opted to go with this simpler patch for a 24 year-old bug
report.

 > Historical side note: jka-compr used to have the ability to do what we
 > want here "transparently" (it changed things like `find-file-noselect`
 > to look for compressed versions of the file, among other things).
 > IIRC it was removed when it got integrated into Emacs (don't know why
 > but I assumed it was too hackish/ugly/costly/brittle).
 >
 > We should arguably re-add this feature, tho maybe not transparent,
 > i.e. let packages who need that request that feature explicitly (like
 > here).
 >

That's good to know, thank you.  And I agree that the feature would be
good to have, but I hope that in the meantime we can go with the updated
patch.