[Pkg-rust-maintainers] Bug#1034939: librust-<crate>-<semver>-dev: missing Breaks+Replaces for librust-mio-dev when upgrading from bullseye

[Peter Green]

On 28/04/2023 18:58, Fabian Grünbichler wrote:
> I see no practical issue with 2 meaning we can't have multiple semver
> suffix packages variants of a single crate installed - having the
> unversioned and one semver suffix package in one suite at any given time
> should already be the exception, having more than that should be even
> more rare,

In an ideal world I would agree, the transition from semver
"n" to semver "n+1" would be complete before the transition
from semver "n+1" to semver "n+2" starts.

I've certainly seen cases where that didn't happen though.
clap springs to mind as a currently ongoing one where we
have versions 2, 3 and 4 of clap in bookworm and clap 2
still has more users than clap 3 and 4 combined.

 >and there should be no need to have them *installed* at the
 >same time since these packages are only used as build deps.

More than one semver of the same crate can be used in the same
build process. Also collapse_features means that crates often end
up in the transitive build-dependency graph of a package even
though they are not actually used in the build.

I feel this is the kind of thing that would rarely cause problems,
but when it does cause problems they would be of the
"painted into a corner" type that are very difficult to deal with.