[Pkg-rust-maintainers] Bug#1124769: Bug#1124769: rustc: FTBFS rustc in Debian Bookworm because of conflict in build deps

[Fabian Grünbichler]

Control: reassign -1 src:rustc-web 1.85.0+dfsg3-1~deb12u3

On Tue, Jan 6, 2026, at 8:41 PM, Sergei Semin wrote:
> Fabian, hi!
>
> Thank you for such quick answer!
>
> You wrote:
>
>> that sounds like your repository setup is incomplete? did you maybe
> forget to also add the corresponding main bookworm repository?
>
> I think my repository setup is complete. [..]

I haven't tried your exact steps, since I don't use docker in any fashion.
But I can reproduce the issue in a plain bookworm chroot as well, it's
just that sbuild (the official way to build packages) uses a different
(build-)dependency resolver than `apt build-dep`.

The actual problem is that rustc-web and cargo-web both have a Provides:
for regular rustc and cargo, but cargo-web's one is unversioned, and thus
a versioned build-dependency on both rustc and cargo (which rustc has)
potentially only picks up rustc-web, but not cargo-web, which is an
invalid combination because of the Conflicts.

Reassigning accordingly, pochu/adilinger feel free to provide further
input, I think the correct solution here is to add a version to cargo-web's
Provides line as well, or drop the version from rustc-web's?

@Sergey: I think you can work around the issue by first installing rustc
and cargo, then running `apt build-dep` again - at least that works in my
reproducer environment.

Fabian