[Pkg-rust-maintainers] Bug#1069687: librust-bitflags-1-dev: fails to co-install

[Helmut Grohne]

Hi Matthias,

On Mon, Apr 22, 2024 at 10:34:11PM +0200, Matthias Geiger wrote:
> This is the same situation as in #1040477. This is an issue wrt how we
> generate the semvers. I image rust-proc-macro-crate-1 would pose the same
> problem. Quoting you from 1040477:

Right!

> Is the only workaround dropping Ma:same here ?

I see very little alternatives. We must choose:

 * Do not combine M-A:same + Provides: foo + Breaks: foo.
 * Fix dose/apt/dpkg to agree on what this means.

If we were to adapt dose and apt, they's simply arrive at the conclusion
that M-A:same would not work here so that really is not what you'd want
here. This amounts to fixing dpkg to allow this very combination in the
same way that apt and dose allow it. So yeah, changing dpkg could be an
option. Ccing dpkg-devel about it.

The first alternative means that we must not combine them at the same
time. As we very much want M-A:same, we must not have this combination
of Provides and Brekas. Keep in mind that they serve slightly different
purposes. We have Breaks + Replaces and you can only replace a real
package but Provides introduce a virtual package. In effect we're
dealing with a package that sometimes is virtual and other times is
real. We can choose different names for these uses. The real package
could be renamed and also provide the virtual facility. All of them
would now provide the virtual one as virtual only and none of them would
have the virtual name. The Breaks and Replaces would be updated to match
the real name.

This may not work for the in-archive situations right now as Breaks and
Replaces may still be necessary for upgrades, but it is something that
may work in future situations of the same kind.

In the mean time, consider that M-A:same presently is a lie. Removing it
is better than continuing to lie. It's not like we must have everything
in perfect multiarch. Even for cross compilation, we often can get away
without M-A:same by only requiring a package for the host architecture.
M-A:same is not the goal. It's a tool and way may consider using other
tools.

Helmut