bug#43725: 28.0.50; Include feature/native-comp into master

[Eli Zaretskii]

If I do this:

   $ touch lisp/emacs-lisp/comp.el
   $ ./src/emacs -Q
   C-h f apropos RET

then I see that Emacs starts natively-compiling comp.el, even though I
already have a comp.eln file in the eln-cache.

This is unlike what happens with the .elc files, where Emacs will
never byte-compile a file without my say-so.  I could perhaps
understand the automatic compilation if there was no .eln file
anywhere in sight, but why should Emacs automatically compile Lisp
files it loads when a .eln file for them does exist?

Does this happen with any .el file, or is comp.el special in some
sense?

One situation where this gets in the way is when I make some changes
in a .el file because I'm testing something or debugging some problem.
In those cases I usually load a .el file manually and later either
undo the changes or make them permanent, and re-byte-compile at that
time.  But with natively-compilation it sounds like I've lost control
on when the file is compiled and which version of it is compiled.

Is this a reasonable default behavior?  Maybe it is reasonable for
users who just use Emacs.  But for developers that constantly make
changes in .el files this could be a nuisance, at least sometimes.