apt, branch 2.9.29

Release 2.9.29

2025-02-14T18:42:49Z

Merge branch 'solver3' into 'main'

2025-02-14T18:30:53Z

Get 3.0 solver mostly in shape See merge request apt-team/apt!451

solver3: Store clauses as the reasons for decisions

2025-02-14T18:08:45Z

So far we only stored the last reason why something was decided, for example, if "A depends B | C" and we assigned B=false, C=false, we'd store "(not) C" as the reason for "(not) A". This gives us only a partial implication graph; after all "C" was not the *sole* reason for not installing A. This has two implications: 1. We cannot do conflict-driven clause learning 2. We cannot print excellent information about why packages cannot be installed (or removed) This commit is incomplete in addressing both; in particular, we always store a clause as a reason for something that is not a root object; whereas MiniSAT would only store a clause on propagation. That is, if A depends B | C, and we install A, then we have to make a choice between B|C. Let's say we pick B, we store 'A depends B|C' as the reason whereas MiniSAT would not store a reason (because it picked the "next best" unassigned literal). Hopefully this is not going to be an issue. The reason is used to calculate the assignments that caused the decision in MiniSAT, but the idea is that we can just treat reason clauses with unassigned values as "no reason". The conflict explanation (WhyStr) has been changed to print the strongest reason; which produces the same result as the previous solution for the test suite. What does this mean? If we look at A depends B|C, let's analyse: Why not A? We return the first assigned value for B|C, likely B. We might have returned C here before as it was the last assignment, but we might also return C here, if B is not assigned. Why B? We return A. If we look at A conflicts B: Why not A? Well B Why not B? Well A Thanks to the structure of the implication graph this is quite simple, but also generalizing this to the CNF format should not be hard. A future version will extend clauses with backlinks to pkgCache::Dependency*, allowing us to print useful information to uses such as "A Depends B | C | D (>= 2)" in the real form, rather than the expanded form which may be "A -> B | C | D=3 | D=2".

solver3: Only enqueue shared dependencies at the package level

2025-02-14T18:08:45Z

Dependencies shared by all versions are enqueued at the package level, so avoid enqueuing duplicates at the version level. This presumably has no meaningful impact on performance, potentially a negative performance impact on some workloads as we now need to find the duplicates again; it can become useful when there is a lot of backtracking. More importantly though this improves error messages, because now we can say that "all versions of foo depend on X", rather than saying "foo=1 depends on X" and you are left wondering why we did not select "foo=2". In this commit though, improved error messages are not implemented, they depend on redesigning the reason tracking to use clauses. Also the rationale tracking includes a lot more dependencies of the form "pkg:arch=version -> pkg:arch" which are annoying. Improved error messages should fold them into one node.

solver3: Remove work rescoring in favor of unit propagation

2025-02-14T18:08:45Z

Instead of expensive rescoring of all outstanding items, use unit propagation to find new units after conflicts. We still count the items when adding them; but unless they are 0 or 1, which they should not be, they don't have any effect: The size field is now effectively static. If the size of an optional clause changed to 1, it is inserted a second time, and then moves up to the top of the optional items per the Work::operator< rules.

solver3: Refactor a debug message

2025-02-14T18:08:45Z

Use Var::toString() to print the variable, instead of duplicating the code :D

test: Remove long obsolete FIXME for solver3

2025-02-14T18:08:45Z

test: Annotate the broken test cases

2025-02-14T18:08:45Z

test-ubuntu-bug-614993: Avoid implicit upgrade-by-source requirement

2025-02-14T18:08:45Z

This allows it to work with solver3 before that feature is implemented. This essentially reverts the change to that test made in 119a8d0ed19a4e946591b9aef7d662e14ca7ece5

ResolveByKeep: Do not pass UPGRADE_ALL to EDSP solver

2025-02-14T18:08:45Z

When we call an EDSP solver from ResolveByKeep(), we are not in an upgrade context: In an upgrade context, we call the solver directly from upgrade.cc instead of doing any Resolve() or ResolveByKeep() calls. This fixes the test-bug-602412-dequote-redirect test case, where ResolveByKeep() was called as part of --fix-missing