Re: Merging MPS a.k.a. scratch/igc, yet again

[Pip Cet via "Emacs development discussions." <emacs-devel@gnu.org>]

On Tuesday, December 10th, 2024 at 04:17, Xiyue Deng <manphiz@gmail.com> wrote:
> Óscar Fuentes ofv@wanadoo.es writes:
> If making MPS available in Debian would help Emacs packaging I'm willing
> to work on this (in the coming weeks as igc may not land with the
> upcoming Emacs 30 release so not in a hurry.)

I think that would be great, even if we decide we cannot make do with an unmodified upstream version of MPS.

> * Does igc require only mps.{h,c} or more sources from the MPS source
> package? It looks like there are many sources and it's autotools
> build script fails with GCC 14.2 in Debian Trixie due to several
> "-Werror"s. It may be easier to just compile and ship the required
> subset, though it may require providing a custom build script.

Ravenbrook recommends building the library directly by compiling mps.c, and that's what I usually do. I still ended up having to remove -Werror from the .mk files, at some point...

> * Does igc work with a dynamically linked MPS library?

It definitely does, because that's what we're using on Android. On other systems, statically-linked code may be very slightly faster, but IMHO packaging a statically-linked Emacs+MPS binary is problematic for a few reasons, just as statically linking to libc would be. (It should go without saying that "we always use it" is not sufficient reason for using a statically-linked library)

> Currently I have
> seen people suggesting that directly compiling the source, which is
> effectively like using MPS as a static library.

That works, and it's what I do on GNU/Linux, but we should probably change our approach there.

> It would be less
> useful to package a static-only library in Debian because in case of
> any issues (usually security) updating the library is insufficient and
> its dependencies would need to be rebuilt as well. Using a dynamic
> library would solve this scalability issue, and it would be good to
> know if igc can work with a dynamically linked MPS.

It definitely can work, and I'll look into switching my builds over to using dynamic linking.

> * Does igc work with the latest tagged version (release-1.118.0) or only
> the latest snapshot? Packaging a tagged version would be easier,
> though working with a snapshot may also work with a bit of extra
> efforts.

It's not quite clear to me yet whether we're going to be able to use unpatched MPS on all architectures (that's somewhat unlikely) or on every architecture except for 32-bit x86 (more likely).

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