bug#48978: 28.0.50; native-comp: Error: File error Creating file with prefix

[Andrea Corallo via "Bug reports for GNU Emacs, the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>]

Eli Zaretskii <eliz@gnu.org> writes:

>> From: No Wayman <iarchivedmywholelife@gmail.com>
>> Cc: 48978@debbugs.gnu.org
>> Date: Sun, 13 Jun 2021 08:51:09 -0400
>> 
>> > What happens if you do the following from the shell prompt:
>> >
>> >   $ emacs -batch -l comp -f batch-native-compile
>> > /usr/share/emacs/28.0.50/lisp/progmodes/etags.el
>> 
>> Here we get the rest of the file-error:
>> 
>> Debugger entered--Lisp error: (file-error 
>> "/usr/share/emacs/28.0.50/lisp/progmodes/etags.el" "Creating file 
>> with prefix" "Permission denied" 
>> "/usr/share/emacs/28.0.50/lisp/progmodes/etags.elc")
>>   signal(file-error 
>>   ("/usr/share/emacs/28.0.50/lisp/progmodes/etags.el" "Creating 
>>   file with prefix" "Permission denied" 
>>   "/usr/share/emacs/28.0.50/lisp/progmodes/etags.elc"))
>>   comp--native-compile("/usr/share/emacs/28.0.50/lisp/progmodes/etags.el")
>>   batch-native-compile()
>>   command-line-1(("-l" "comp" "-f" "batch-native-compile" 
>>   "/usr/share/emacs/28.0.50/lisp/progmodes/etags.el"))
>>   command-line()
>>   normal-top-level()
>> 
>> Which is obviously a permissions error.
>> 
>> > Also, is /usr/share/emacs/28.0.50/lisp/progmodes writable by 
>> > your
>> > user?
>>  
>> Permissions for the directory are as follows:
>> 
>> drwxr-xr-x 2 root root 4.0K Jun 13 08:48 
>> /usr/share/emacs/28.0.50/lisp/progmodes/
>> 
>> ^Looks like that's the problem!
>
> Yes, that's what I thought was happening.
>
>> I'm using an AUR script to install Emacs.
>> I see now there was a recent change to that script which modifies 
>> the permissions of directories:
>> 
>> https://aur.archlinux.org/cgit/aur.git/commit/?h=emacs-git&id=dca21d899ec2b1390526a300c7a617a22165dbda
>> 
>> Willing to bet that's the cause of the error here.
>> I'll contact the maintainer of that installation script.
>> Thanks for the response and sorry for the noise (though, I do 
>> think there may be a bug with the way that file-error is being 
>> reported).
>
> It isn't noise: Emacs shouldn't really try creating files in that
> directory, not when native-compiling in the background.
>
> Andrea, this happens because native-compilation calls
> byte-compilation, which then attempts to create the temporary .elc
> file in the same directory where the .el file lives.  I show the
> backtrace which leads to this issue below.
>
> Do we really need that temporary file for the purposes of
> native-compilation, or could we disable its creation?

Agree, I think we can (and should) disable its creation when
`byte+native-compile' is non-nil.

> If the latter,
> I think we should, because in general there's no reason to assume the
> /usr/share tree is writable by unprivileged users.

Right I pushed dc4ac39b26, it should do the job.  Nick could you have a
look if the it solves the problem?

Thanks

  Andrea