bug#61880: Native compilation fails to generate trampolines on certain scenarios

[Eli Zaretskii]

> From: Sergio Durigan Junior <sergiodj@sergiodj.net>
> Date: Tue, 28 Feb 2023 19:13:58 -0500
> 
> While investigating a few bugs affecting Debian's and Ubuntu's Emacs
> packages (for example,
> https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1028725), I stumbled
> upon a problem that's affecting native compilation on Emacs 28.1+,
> currently reproducible with git master as well.
> 
> I haven't been able to fully understand why the problem is happening,
> but when there are two primitive functions (that would become
> trampolines) being used sequentially, Emacs doesn't generate the
> corresponding .eln file for the second function.
> 
> I spent some time investigating the problem and came up with a "minimal"
> reproducer:
> 
> --8<---------------cut here---------------start------------->8---
> (require 'cl-lib)
> 
> (defmacro foo--flet (funcs &rest body)
>   "Like `cl-flet' but with dynamic function scope."
>   (declare (indent 1))                                                        
>                                                                               
>                               
>   (let* ((names (mapcar #'car funcs))
>          (lambdas (mapcar #'cdr funcs))
>          (gensyms (cl-loop for name in names
>                            collect (make-symbol (symbol-name name)))))
>     `(let ,(cl-loop for name in names
>                     for gensym in gensyms
>                     collect `(,gensym (symbol-function ',name)))
>        (unwind-protect
>            (progn
>              ,@(cl-loop for name in names
>                         for lambda in lambdas
>                         for body = `(lambda ,@lambda)
>                         collect `(setf (symbol-function ',name) ,body))
>              ,@body)
>          ,@(cl-loop for name in names
>                     for gensym in gensyms
>                     collect `(setf (symbol-function ',name) ,gensym))))))
> 
> (defun bar (file)
>   (and (file-exists-p file) (file-readable-p file)))
> 
> (defun test ()
>   (foo--flet ((file-exists-p (file) t)
>               (file-readable-p (file) nil))
>     (message "%s" (bar "/home/sergio/.lesshst"))))
> --8<---------------cut here---------------end--------------->8---
> 
> When I run it using the following Emacs:
> 
> --8<---------------cut here---------------start------------->8---
> GNU Emacs 30.0.50
> Development version 68cc286c0495 on master branch; build date 2023-02-28.
> --8<---------------cut here---------------end--------------->8---
> 
> here is the output I see:
> 
> --8<---------------cut here---------------start------------->8---
> $ emacs -batch -Q -l t.el -f test -L .
> Error: native-lisp-load-failed ("file does not exists" 
> "/home/sergio/.emacs.d/eln-cache/30.0.50-23de7b18/subr--trampoline-66696c652d7265616461626c652d70_file_readable_p_0.eln")
>   debug-early-backtrace()
>   debug-early(error (native-lisp-load-failed "file does not exists" 
> "/home/sergio/.emacs.d/eln-cache/30.0.50-23de7b18/subr--trampoline-66696c652d7265616461626c652d70_file_readable_p_0.eln"))
>   
> native-elisp-load("/home/sergio/.emacs.d/eln-cache/30.0.50-23de7b18/subr--trampoline-66696c652d7265616461626c652d70_file_readable_p_0.eln")
>   comp-trampoline-search(file-readable-p)
>   comp-subr-trampoline-install(file-readable-p)
>   fset(file-readable-p (lambda (file) nil))
>   (progn (fset 'file-exists-p #'(lambda (file) t)) (fset 'file-readable-p 
> #'(lambda (file) nil)) (message "%s" (bar "/home/sergio/.lesshst")))
>   (unwind-protect (progn (fset 'file-exists-p #'(lambda (file) t)) (fset 
> 'file-readable-p #'(lambda (file) nil)) (message "%s" (bar 
> "/home/sergio/.lesshst"))) (fset 'file-exists-p file-exist
> s-p) (fset 'file-readable-p file-readable-p))
>   (let ((file-exists-p (symbol-function 'file-exists-p)) (file-readable-p 
> (symbol-function 'file-readable-p))) (unwind-protect (progn (fset 
> 'file-exists-p #'(lambda (file) t)) (fset 'file-re
> adable-p #'(lambda (file) nil)) (message "%s" (bar "/home/sergio/.lesshst"))) 
> (fset 'file-exists-p file-exists-p) (fset 'file-readable-p file-readable-p)))
>   test()
>   command-line-1(("-l" "t.el" "-f" "test" "-L" "."))
>   command-line()
>   normal-top-level()
> Native elisp load failed: "file does not exists", 
> "/home/sergio/.emacs.d/eln-cache/30.0.50-23de7b18/subr--trampoline-66696c652d7265616461626c652d70_file_readable_p_0.eln"
> --8<---------------cut here---------------end--------------->8---
> 
> Do note that this is already affecting a few packages, like buttercup
> (see https://github.com/jorgenschaefer/emacs-buttercup/issues/230) and
> emacs-web-server, for example.
> 
> Please let me know if you need more information regarding the problem.

Thanks.

Andrea, can you please look into this?  I guess if this happens in
Emacs 28 and on master, it also affects Emacs 29, so I hope this can
be fixed quickly and safely.  TIA.