bug#60996: 29.0.60; Native compile fails to remove temp file for trampoline

[Eli Zaretskii <eliz@gnu.org>]

> Cc: 60996@debbugs.gnu.org
> Date: Tue, 24 Jan 2023 14:56:00 +0200
> From: Eli Zaretskii <eliz@gnu.org>
> 
> But first, I'd like to understand whether indeed it could happen that
> we are deleting a temporary .eln file for a trampoline we just
> compiled when we are still using that .eln file.  If this happens,
> we'd need to find a way to delay the deletion till Emacs is about to
> exit or something.

I keep looking at the backtraces you provided, this:

> Debugger entered--Lisp error: (permission-denied "Removing old name" 
> "Permission denied" "c:/Users/ajm/AppData/Local/Temp/comp-lambda-MTAMbr...")
> delete-file("c:/Users/ajm/AppData/Local/Temp/comp-lambda-MTAMbr...")
>    #f(compiled-function () #<bytecode 0xb2aa5c0c9e24501>)()
>    comp--native-compile((lambda (arg0 &optional arg1 arg2 arg3) (let ((f 
> #'format-mode-line)) (funcall f arg0 arg1 arg2 arg3))) nil nil)
>    comp-trampoline-compile(format-mode-line)
>    comp-subr-trampoline-install(format-mode-line)
>    advice--add-function(:around (#f(compiled-function () #<bytecode 
> 0x3c5d8019df7e91>) . #f(compiled-function (gv--val) #<bytecode 
> 0x8fdecbbba7cb3c2>)) delight--format-mode-line nil)
>    advice-add(format-mode-line :around delight--format-mode-line)
>    require(delight nil t)

And this:

> delete file("path/to/comp-lambda-XXXXX.eln")
> comp--native-compile((lambda (...) ...))
> comp-trampoline-compile(function-name)
> comp-subr-trampoline-install(function-name)
> advice--add-function(...)
> advice-add(function-name ...)

and I still don't have a clear picture regarding which code calls
delete-file and why.  For example, the first backtrace above says that
comp--native-compile calls delete-file via some byte-compiled
function, not directly.  But what is that byte-compiled function? can
you figure that out?

There is a direct call to delete-file in comp--native-compile, but is
that the call which fails?  And if so, why does it fail?  Which code
created the .eln file that comp--native-compile tries to delete?

Andrea, can you please describe in detail what happens, step by step,
when comp-subr-trampoline-install is called like above, to compile a
trampoline for an advised function?  What is that file which
comp--native-compile is deleting at the end?

Thanks.