Re: builds are getting slower?

[Glenn Morris]

>> >> And why exactly this code needs to run when we need to byte-compile
>> >> Lisp files, btw?

It's run whenever Emacs visits a file, thus making code efficiency very
important.

>> Not really.  It loads the files, and loading the files sets the
>> directory-local variables.  I don't think it is a good idea to use them
>> for byte compilation even though I have to admit that a directory-wide
>> setting of `lexical-binding' would seem less ugly than putting it in
>> every file manually.  But it sounds like a recipe for trouble.
>
> We can disable that.

IIRC, Stefan was against this kind of thing; ie, making tweaks to the
build process to work around an issue that would otherwise be present
in normal Emacs usage. The feeling was that we should fix issues
properly, for everyone, rather than hiding them. The context in which
it came up before was VC, which, like dir-locals, is another operation
that runs every time Emacs visits a file, so also needs careful
treatment. I think I agree with him more now then I did back then.

(Outside of that general principle, I can actually see dir-locals
possibly being wanted during byte-compilation in future.)

Irrespective of the details, personally I'd like to see this code
rewritten to avoid requiring seq (which it does whenever Emacs visits a
file) and map (which it does whenever a dir-locals is present); ie avoid
non-preloaded libraries.

But you are right that actually profiling things is the place to start.