Re: MPS inclusion in IGC branch - Re: License ramifications of distributing MPS with Emacs

[Eli Zaretskii]

> From: Stefan Monnier <monnier@iro.umontreal.ca>
> Cc: jb@jeremybryant.net,  pipcet@protonmail.com,  emacs-devel@gnu.org,
>   eller.helmut@gmail.com,  gerd.moellmann@gmail.com,
>   stefankangas@gmail.com,  acorallo@gnu.org
> Date: Wed, 21 May 2025 15:12:08 -0400
> 
> >> >> Hmm... So we're thinking of "vendoring" MPS?
> >> >> I'm not very favorable to vendoring.  It's often attractive in the short
> >> >> term, but it dumps extra work on distributions like Debian which will
> >> >> need to "unvendor" the library, and also can bring long-term maintenance
> >> >> cost to sync with other versions.
> >> > Why would they need to "unvendor" it, whatever that means?
> >> That's the principles/conventions they follow.  As part of packaging,
> >> the "DM" has to make sure they don't end up with "hidden copies" of
> >> a library.
> > What is a "hidden copy" of a library?
> 
> A copy of a library (such as MPS) bundled inside another package.

And why is that a problem for the distro, why do they have to make
sure it doesn't happen?

> >> >> So, I'd vote for "keep it as a separate library for now".
> >> > What do we do in that case with the platform-specific patches that
> >> > Emacs needs to apply to the library?
> >> Can we get them integrated upstream?
> > Unlikely.
> 
> Why not?

Because patches submitted to them never got into the upstream, and bug
reports are still open.  And because the last release was 2 years ago,
and the one before that 7 years ago.  Look at their Issues: I see 10
issues there opened by Gerd, Pip, and others on behalf of Emacs since
more than a year ago, and they are still open.  Can we live with such
level of support in a library that implements GC, which is one of the
most important functionalities in Emacs?

IMO, if we don't fork the library, we will need to maintain patches
and workarounds for it in the tree, which all but makes the advantages
of using an external library irrelevant.

> [ Side note: even if we don't vendor that library, it would make sense
>   to host a copy of it on another service than Github, both because
>   I don't think we should advertise Github and because Microsoft seems
>   to want to reduce Github's access for anonymous users.  ]

I don't see how Github is relevant, since using MPS as an external
library means people will use what their distro provides or (rarely)
download and build the release tarballs.  Also, we don't do anything
like that for tree-sitter and its grammar libraries, for example,
although they are all on Github.  Anyway, this is a tangent, and very
minor compared to the above serious (IMO) problems.