bug#52773: Master and (probably) emacs-28: locate-library hides .eln files.

[Alan Mackenzie]

Hello, Emacs and Andrea.

With a native compiled recent master branch, do:

    emacs -Q
    M-x locate-library <RET> files <RET>

The result in the echo area is something like:


    Library is file ~/emacs/emacs.git/sub-master-5/lisp/files.el
                                                             ^^^

..  This is wrong.  The Emacs is _NOT_ running uncompiled Lisp, it's
running native compiled files.  The reply should be a file name ending
in ".eln".

This problem is surely also in the emacs-28 branch.

#########################################################################

The cause of the problem is in `locate-file' in files.el.  There, if a
..eln file is found, it's corresponding .el source is looked up in a hash
table, and the .el name returned instead.

This mechanism was inserted by the following patch:

commit 3224a443060a5f21bb910064fc06fe4432810355
Author: Andrea Corallo <akrl@sdf.org>
Date:   Sun Jul 19 10:46:24 2020 +0200

    Move eln files into dedicated cache directories

    When loading a elc file search for a corresponding eln one into
    `comp-eln-load-path' directories and load it if available.
    `comp-eln-load-path' contains by default two directory (user and
    system one).

It seems there is some use case for which returning the .el file name in
place of the .eln is appropriate.  It isn't appropriate for
locate-library.

I would suggest moving the hash table mechanism out of locate-file, and
into the other function which calls locate-file, where the substitution
is wanted.

-- 
Alan Mackenzie (Nuremberg, Germany).