Re: Speeding up the bootstrap build - a quick hack.

[Eli Zaretskii]

> From: Robert Pluim <rpluim@gmail.com>
> Date: Tue, 18 Jan 2022 16:13:23 +0100
> Cc: Alan Mackenzie <acm@muc.de>, emacs-devel@gnu.org
> 
> >>>>> On Tue, 18 Jan 2022 15:35:42 +0100, Robert Pluim <rpluim@gmail.com> 
> >>>>> said:
>     Stefan> In an ideal world the second rule would not have `bytecomp.elc` 
> as its
>     Stefan> target but would have something like `bytecomp.eln` instead, but 
> we have
>     Stefan> not yet been able to teach Make how to compute the name of the 
> generated
>     Stefan> `.eln` file (it's not just `bytecomp.eln` but includes some hash 
> of the
>     Stefan> Emacs binary).
> 
>     Robert> Thereʼs no other file or directory name that contains that hash? 
> Could
>     Robert> we do a dummy compile of an empty .el using the native compiler 
> and
>     Robert> derive the hash from that? (and then compile the native compiler 
> with
>     Robert> the byte compiler).
> 
> Answering my own question:
> 
> src/emacs -batch --eval '(message "%s" (comp-el-to-eln-filename \
> "./lisp/emacs-lisp/bytecomp.el" (car (last \
> native-comp-eln-load-path))))' 2>&1
> 
> seems to give the right answer.

Yes, and that needs the working Emacs binary, so it doesn't come for
free.  On top of that, some of the COMPILE_FIRST targets end up in
that directory, others it its preloaded/ subdirectory: something else
that only Emacs knows about.