Re: How does Emacs load a non-existent .el file?

[Konstantin Kharlamov <Hi-Angel@yandex.ru>]

On Fri, 2024-03-01 at 14:22 +0200, Eli Zaretskii wrote:
> > From: Konstantin Kharlamov <Hi-Angel@yandex.ru>
> > Date: Fri, 01 Mar 2024 13:52:30 +0300
> > 
> > I was just looking whether it's too hard to add an option for
> > reading
> > from stdin (a very requested feature¹). Long story short, I presume
> > command line parsing happens in `lisp/startup.el`, function
> > `(command-
> > line-1)`. That's where the weirdness starts. Since it is an ELisp
> > file,
> > I figured to avoid recompiling I can move its `.elc` file out of
> > the
> > way and just do edits to `startup.el` directly. Turned out though,
> > not
> > only Emacs does not notice these edits, it somehow manages to load
> > the
> > file when it does not exist!
> > 
> > So e.g. I did a `sudo rm /usr/share/emacs/30.0.50/lisp/startup*`,
> > so no
> > .el or elc files. But starting up `emacs -Q` and asking it `C-h f
> > command-line-1` still results in Emacs answering that such function
> > exists, except the help buffer doesn't have a link to it.
> > 
> > I am thoroughly confused. Any idea what's going on here?
> 
> Yes: startup.el is preloaded, see lisp/loadup.el.  So if you change
> it, you need to rebuild Emacs to let the changes have their effect at
> startup.  You can also load startup.el manually into a running
> session, and then invoke functions you've changed, but that will only
> be useful if what you are changing is not some special behavior that
> happens only at startup.

Okay, I see, so the `startup.el` is a dummy file that's not being read.
I wonder if it's too hard to add to `*Help*` buffer mention that
certain functions are not being read from the file where the buffer
claims that they reside.

> > https://superuser.com/questions/31404/how-to-make-emacs-read-buffer-from-stdin-on-start
> 
> There are a few answers there that solve the problem, so I'm not sure
> what else are you trying to do, and why.

I see only one answer that is more or less convenient, which is `emacs
--insert <(echo 123)`. The problem with this one is that `--insert` is
not supported in `emacsclient`; and in the context of the problem such
support would be useless anyway because it would make `emacsclient`
paste the text to a random buffer which is not at all something a user
expects.

The rest of answers require jumping through the hoops with either
writing separate scripts or using a temporary file.

I agree with the opinion of one of the commenters here: this is
absolutely basic feature that most editors have. Not having it in Emacs
is very strange.