Strange errors of make compile concerning save-excursion/set-buffer

[Makarius]

This is GNU Emacs 23.2.1 on Mac OS.

Byte-compilation via make EMACS=/Applications/Emacs.app/Contents/MacOS/Emacs compile fails with strange errors like this:

coq/coq.el:291:8:Error: `save-excursion' defeated by `set-buffer'

The source in question in this case is

(defun proof-last-locked-span ()
  (save-excursion ;; didn't found a way to avoid buffer switching
    (set-buffer proof-script-buffer)
    (span-at (- (proof-unprocessed-begin) 1) 'type)
    )
  )

The same for isar, lego etc. Maybe this indicates an actual instability that was undetected so far.

[David Aspinall]

No, I don't think there is an instability necessarily. This is a new compiler warning with 23.2, which is quite confusing. It is probably aimed at people who did not properly understand the behaviour of save-excursion anyway. See lengthy discussion here:

​http://thread.gmane.org/gmane.emacs.devel/118710

The usage above is absolutely fine (no move of point in the temp buffer) so the warning is spurious.

Our compile is set to strictly treat warnings as errors so halts.

With newer Emacs API there are cleaner ways of doing this which we can switch to.

Unfortunately at the moment I can't build Emacs 23.2, so I've fixed the cases I found by looking around quickly. (A dump of warnings would be useful if you turn off the strict behaviour of make compile)

[David Aspinall]

OK, struggled a while with library mess and built latest Emacs and patched the remaining cases (I hope correctly, will this get enough testing for PG 4.0?).

The idiom is rife in loads of Emacs lisp as it was a prototypical usage demonstrated in documentation, but =with-current-buffer= is usually what's wanted.

[Makarius]

stderr of "make compile", with (setq byte-compile-error-on-warn nil)

[Makarius]

BTW, GNU Emacs 23.2.1 is available as "no non-sense" Mac OS application from ​http://emacsformacosx.com/

Cygwin 1.7.5 also provides 23.2.1 by default.

[David Aspinall]

Thanks for the log. I forgot to commit the remainder of the fixes. Done now, should compile cleanly without warnings.