apt/apt-pkg/solver3.h, branch 2.9.33

solver3: Fix Recommends/Suggests vs Enhances confusion

2025-03-12T17:52:16Z

We accidentally considered an Enhances a reason to keep a package installed, which of course it is not, fix the determination of "existing soft dependency" to only include soft dependencies that should keep a package installed in the autoremover to solve the issue. This also fixes edsp/mantic-upgrade-rel-to-2024-05-29.edsp to not install llvm-13-dev for clang-13 which is an installed package with no upgrade. Also ensure we stop after the first match; the DependsList() is ordered by decreasing priority and we don't want to override Recommends by Suggests in case a package declares both... LP: #2101800

solver3: Do not prefer new installs over manually installed obsoletes

2025-03-09T13:53:53Z

Only move obsolete packages last that are automatically installed, as we don't want to remove manually installed obsolete packages. Add some missing const annotations to the operator[] arguments as well that were needed. LP: #2100247

solver3: Verbose error messages

2025-03-08T22:18:05Z

Introduce a new function, LongWhyStr() that returns a longer reason for why something is being installed (or not). This does the same path walk as the other function does, but it renders the clauses at each level, and one per line, so the whole output is a lot more informative. It is a separate function to keep the existing debug messages use the simple single line implication graph We remove the other special case in AddWork() for empty solutions to mke use of the general case in Solve() instead, and then adapt the case in Solve() to the same case as in Enqueue(). This also happens to fix the bug that when we encountered an empty clause we just printed the clause had no solution, but not how we got to install the package with the clause. Adapt the test suite for the changes which is an annoying amount of paperwork.

solver3: Support pretty printing clauses

2025-03-06T19:07:00Z

This will print the underlying dependency which is nicer to read.

solver3: cleanup operators for Var

2025-03-06T19:06:40Z

Particularly, use single line and implement operator!=

solver3: refactor: Return inserted Clause in AddWork()

2025-03-06T19:06:40Z

This avoids relying on the inserted clause being at the back of the clauses vector.

solver3: Simplify Var pointer tagging

2025-03-06T19:06:40Z

Use an integer and tag the lowest bit manually. This makes it much easier to next convert this into a literal. Add some constexpr and remove an unnecessary assertion on CastPkg().

Add missing #include

2025-02-15T15:54:38Z

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: 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.