bug#66534: 30.0.50; [PATCH] Expand file-name of ~/.emacs before attempt to load it

[Christoph]

On Sat, Oct 14, 2023 at 8:54 AM Eli Zaretskii <eliz@gnu.org> wrote:
>
> > Date: Fri, 13 Oct 2023 20:41:16 +0200
> > From:  Christoph via "Bug reports for GNU Emacs,
> >  the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>
> >
> > I noticed that during startup, emacs tries to load ~/.emacs (with
> > different extensions) many times over.  You can see this by using
> > strace and tracing the openat syscall.  The problem is, that `load'
> > does not expand the ~/ in the filename passed to it.  So it does not
> > recognize the file as being absolute and tries to resolve it using
> > the load-path.
> >
> > While resolving the path in the openp function in lread.c,
> > `expand-file-name' is used with the default directory being the
> > elements of the load-path.  Since for `expand-file-name', ~/.emacs is
> > an absolute path, it returns the path unchanged, and load tries to
> > load ~/.emacs many times over.
>
> I don't understand what you are saying here.  The last sentence is
> incorrect, as evidenced by the following:
>
>   (expand-file-name "~/.emacs" "/tmp")
>    => "/home/eliz/.emacs"
>
> IOW, "~/.emacs" is indeed treated by Emacs as an absolute file name,
> but expand-file-name does NOT return "~/.emacs" unchanged.

What I meant is "unchanged" in the regard to the default
directory. You can give any default directory to expand-file-name and
it will always return the first argument in its expanded form, if the
expanded form of the first argument is an absolute path.

>
> So please explain what exactly is the problem you see here, and in
> particular what issues that problem causes in your case.
>
> Thanks.

If you start Emacs without an ~/.emacs file, and with using .emacs.d
and not .config/emacs, I think there is a difference as well, Emacs
will try to load ~/.emacs `(length load-path)' times.  If I start
Emacs with strace -e openat I see the following lines 147 times:

openat(AT_FDCWD, "/home/chris/.emacs", O_RDONLY|O_CLOEXEC) = -1 ENOENT
(No such file or directory)
openat(AT_FDCWD, "/home/chris/.emacs.gz", O_RDONLY|O_CLOEXEC) = -1
ENOENT (No such file or directory)
openat(AT_FDCWD, "/home/chris/.emacs.so", O_RDONLY|O_CLOEXEC) = -1
ENOENT (No such file or directory)
openat(AT_FDCWD, "/home/chris/.emacs.so.gz", O_RDONLY|O_CLOEXEC) = -1
ENOENT (No such file or directory)
openat(AT_FDCWD, "/home/chris/.emacs.elc", O_RDONLY|O_CLOEXEC) = -1
ENOENT (No such file or directory)
openat(AT_FDCWD, "/home/chris/.emacs.elc.gz", O_RDONLY|O_CLOEXEC) = -1
ENOENT (No such file or directory)
openat(AT_FDCWD, "/home/chris/.emacs.el", O_RDONLY|O_CLOEXEC) = -1
ENOENT (No such file or directory)
openat(AT_FDCWD, "/home/chris/.emacs.el.gz", O_RDONLY|O_CLOEXEC) = -1
ENOENT (No such file or directory)

But Emacs should only try to load the file once.  The problem is that
the path to ~/.emacs is not expanded before it is handed to `load' and
load basically does:

(dolist (path load-path)
  (low-level-load (expand-file-name "~/.emacs" path)))

where low-level-load is some magic function which really loads a file.
There is off course more going on, like iterating over the extension
and such, but I want to keep it simple, since I am not familiar with
it at all.

`load' does check if the given path is absolute and
changes its behavior.  If the path is absolute, `load' does not take the
load-path into account, but paths beginning with "~/" are not recognized as
beeing absolute, hence the paths should be expanded before passing them
to `load'.

Because all the other paths to init files (early-init.el and init.el)
are expanded before they are passed to `load', I think "~/.emacs"
should be expanded as well.

There is also the question if `load' itself should be able to handle
paths that begin with "~/" correctly, or if the user is expected to
expand paths before passing them to `load'.

Regards, Christoph