bug#67005: 30.0.50; improve nadivce/comp/trampoline handling

[Andrea Corallo <acorallo@gnu.org>]

Stefan Monnier <monnier@iro.umontreal.ca> writes:

>>  (defcustom native-comp-never-optimize-functions
>> -  '(eval
>> -    ;; The following two are mandatory for Emacs to be working
>> -    ;; correctly (see comment in `advice--add-function'). DO NOT
>> -    ;; REMOVE.
>> -    macroexpand rename-buffer)
>> +  ;; Do not include functions `macroexpand' or `rename-buffer' as
>> +  ;; default values here.  Despite the previous "DO NOT REMOVE"
>> +  ;; warnings these are no longer needed.  See also the comment on
>> +  ;; `advice--add-function' and bug#67005.  FIXME: But do include
>> +  ;; `eval' as temporary (?) remedy for bug#67141.
>> +  '(eval)
>>    "Primitive functions to exclude from trampoline optimization.
>
> I'm not sure I like the idea of keeping the whole history in comments.
> I suggest you try and trim it down to the part that seems likely
> to reoccur, like "We used to list those functions that were advised
> during preload but we now prefer to disallow them in `advice-add`".
>
>> In `addvice--add-function' I wanted to at least preserve the comment
>> from my initial patch (see attachment to
>> https://yhetil.org/emacs-bugs/874jhv9921.fsf@sappc2.fritz.box/).  I
>> think it might help historical research if for that removal there is
>> something that a "git blame" could be hooked onto.
>
> `C-x v h` is your friend.  It was weird in the fist place to put the
> trampoline stuff there (e.g. it's specific to functions stored in symbols so
> it would have been more logical to put it into `advice-add` instead), so
> it doesn't seem very likely that this will re-occur.
>
>>  <<>>"
>> +  ;; Actively disallow function advices (here) and advices in general
>> +  ;; on primitives (in `comp--install-trampoline') during bootstrap
>> +  ;; for the following reasons:
>> +  ;; - Advices in Emacs' core are generally considered bad style.
>> +  ;; - `Snarf-documentation' looses docstrings of advised dumped
>> +  ;;   functions (bug#66032#20).
>> +  ;; - Native compilation does not generate trampolines for advised
>> +  ;;   primitives while loadup.el executes.
>
> I don't think this last point is true/relevant, is it?
> IIUC it would use a "normal funcall", which doesn't need a trampoline.
>
>>    ;; TODO:
>>    ;; - record the advice location, to display in describe-function.
>> -  ;; - change all defadvice in lisp/**/*.el.
>> -  ;; - obsolete advice.el.
>> +  (when purify-flag
>> +    (error "Invalid pre-dump advice on %s" symbol))
>>    (let* ((f (symbol-function symbol))
>>
>> What do you think?
>
> Beside the comments about the comments, it's a +1 from me.

I agree with all the comments made by Stefan, with those implemented +1
for me as well.

Thanks

  Andrea