[Pkg-rust-maintainers] Bug#1102083: Bug#1102083: Bug#1102083: src:rust-rebuildctl: fails to migrate to testing for too long

[Paul Gevers]

Hi,

On 05-04-2025 16:33, Peter Green wrote:
>> Is there something I can improve on this front? In other words, how 
>> can the design become smarter?
> 
> It's hard to answer this because I don't really understand exactly
> how the scheduler works, but what I frequently see is.
> 
> 1. The set of pins that britney chooses don't work.
> 2. The fallback dependency solver is invoked, this successfully
>     installs the packages, but causes a mismatch between the tests
>     (taken from testing) and the package under test (taken from unstable
>     due to the fallback dependency solver).
> 3. The mismatch between tests and package under test causes a failure.
> 
> This often happens in complex dependency graphs, where some but not
> all of the dependencies in the graph are broken by the update.
> or where some dependencies exist in unstable but not in testing
> or vice-versa.
> 
> We can often workaround this by tightening dependencies or adding
> breaks but each time we do that it resets the tests and the migration
> delay time, it can also tie together the testing migration of
> things that do not need to be tied together.
> 
> I don't know how exactly britney choses what packages to pin, but
> it often falls short of the set of "packages that must migrate
> together according to the recursive interpretation of the
> "migrates after"/"blocked by" in the excuses.


I suspect this is related to the heavy use of Provides in the rust 
ecosystem. I suspect that what's missing is the logic (potentially only 
in the autopkgtest policy, but maybe in all policies) to treat a 
src:package that is the sole provider of a certain Provides similar like 
it would treat the source of a real binary of that name.

That indeed is already long time on my TODO list to investigate (and fix 
if I'm right), but I never had the tuits to start on it.

Paul

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