Fix assertion failure when a package constrains itself#230
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This is admittedly a strange thing to do, but here was the rationale: https://gitlab.com/redhat/centos-stream/rpms/centos-stream-release/-/commit/ce231c10b48cb4ddde860bfc9d6f79c76ba92e0a I believe the semantics here are basically "if this package is installed, you must not install another provider, and if another provider is installed, you cannot install this package". |
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Let me know the ideal way to provide tests, unless you want to do it |
baszalmstra
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The constraint introduces a tautology. I think a more technically correct approach would be to (not crash and) block the package from being installable using an assertion. This would be the same as when this is done through a transitive dependency (e.g. A depending on B, which constrains A). I don't think skipping the clause is the right approach. But maybe I misunderstand the use-case?
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So, it's a package that is installed and can be updated (on my CentOS Stream dev container it's at release 21)
I haven't tracked down exactly what libsolv is doing to handle this scenario, but libsolv / DNF must be handling it somehow. Probably it's doing something similar. |
dralley
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When a package both provides and conflicts with the same capability (example: in CentOS Stream, "centos-stream-release" provides "system-release" and also conflicts with "system-release"), the constrains clause would try to forbid the package from coexisting with itself. This caused WatchedLiterals::constrains to panic with "both literals cannot be false" because both watched literals referred to the same variable. Skip self-referential constrains entries: a package that is already in the solution obviously cannot constrain itself out of it. Assisted-By: Claude Opus 4.6 <noreply@anthropic.com>
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Ah, so here's some libsolv documentation: So, libsolv does indeed do basically the same thing as this patch, but it's behind a solver configuration flag, because the desired behavior varies by ecosystem. Would you want to do something similar (or is there already a mechanism for solver config options)? Unrelated: looks like the multiversion code is right there as well. And that might need a similar solution as well |
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Is that then something we should not just solve in the dependency provider itself? Simply dont return self-referential constraints? We should still solve the crash of course, but I think we should backtrack in that case. |
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When a package both provides and conflicts with the same capability (example: in CentOS Stream, "centos-stream-release" provides "system-release" and also conflicts with "system-release"), the constrains clause would try to forbid the package from coexisting with itself. This caused WatchedLiterals::constrains to panic with "both literals cannot be false" because both watched literals referred to the same variable.
Skip self-referential constrains entries: a package that is already in the solution obviously cannot constrain itself out of it.
Assisted-By: Claude Opus 4.6 noreply@anthropic.com