bug#2807: Subject: 23.0.90; etags can't access .el.gz files

[Francesco Potortì]

>MON KEY <monkey@sandpframing.com> writes:
>
>> in dir /usr/share/emacs/23.0.90/lisp
>> M-x shell:
>> bash-3.1$ etags ./*.el.gz
>>
>> when true:
>> (equal tags-file-name "/usr/share/emacs/23.0.90/lisp/TAGS")
>>
>> M-x tags-search
>> tags-search
>>
>> I get this error:
>> `next-file: Opening input file: no such file or directory,
>> /usr/share/emacs/23.0.90/lisp/abbrev.el'
>
>I can confirm that this bug is still present in Emacs 24.
>
>The problem is simply that etags puts the non-gz file name in the TAGS
>file.  Like this:
>
>font-core.el,502
>
>Which means that Emacs isn't able to find the font-core.el.gz file.

Etags manages compressed files so that the generated TAGS file contains
the uncompressed file name, independently of whether the file on disk is
compressed or not.

The rationale for this behaviour is that the TAGS file does not contain
info about the compression status of a file.  This makes sense in the
case that when you use an editor you either have an uncompressed file on
disk or your editor is capable of finding the compressed version given
the uncompressed name.

I seem to remember that in past times Emacs was able to do that when
jka-compr was loaded, but I may be wrong.  I think that the solution
should be that etags.el cares about looking for possible compressed
versions of file names contained in TAGS file.

By the way, the xz compressor should be added to the list of known
compressors in etags.c, and the doc strings, man page and info updated
accordingly.