[Pkg-rust-maintainers] Bug#1126584: Bug#1126584: rustc: build stage0 orig tarball from Debian builds

[Fabian Grünbichler]

On Thu, Jan 29, 2026, at 9:32 AM, Emilio Pozuelo Monfort wrote:
> Package: rustc
> Version: 1.91.1+dfsg1-1
> Severity: normal
>
> Hi,
>
> rustc includes a script, debian/make_orig-stage0_tarball.sh, to create a
> stage0.orig.tar.xz that can be used to bootstrap rustc. I don't think that's
> used much, since new updates in Debian sid will use X-1 from sid to build.
> However, when uploading a (much newer) version to (old)stable, we don't have
> X-1, so we need to create and use a -stage0 tarball.

It is mainly used for rebootstrapping when ports/archs get out of sync. But I
guess that might also have fallen out of favor with cross builds mostly working
nowadays.

> The issue I find is that upstream doesn't support some of our release
> architectures, so when doing these backports, we lack a way to bootstrap the
> new version on those architectures. See for example [1].

Yes.

> One possibility would be to create the -stage0 tarballs using Debian 
> sid packages
> for X-1. I haven't looked in detail, but perhaps we would need 
> statically linked
> binaries, which could be done in an extra build and placed in a 
> rust-static .deb.
> Then make_orig-stage0_tarball could look for those .debs from 
> snapshot.debian.org.
>
> Thoughts?

I think for builds using those stage0 tarballs targeting stable we have three
options:
- build a static variant on every unstable upload
- provide a script that cross-builds the missing stage0 targets (either using upstream build, or using an arch that has an upstream stage0 as starting point by doing a cross package build?)
- use backports packages as stage0 input

I think I'd favor the latter, since I already do the work for those ;)

In recent history I think libgit2 was the only library pulled in that I had
to backport as well (that was for Bookworm and for unofficial backports).
It maybe would have been possible to avoid that by patching more aggressively.

Of course, that would *only* help for Trixie, not Bookworm or older. If you
need to support those, only the static or cross build variants would work at
at the moment.

Fabian