apt/test/integration/test-release-candidate-switching, branch main

solver3: Use classical watchers for propagation

2026-01-31T16:30:20Z

Instead of tracking dependencies and reverse dependencies, install classical watchers. This vastly streamlines the propagation code and allows us to easily switch to literals in the next step. This implementation watches _all_ solutions rather than using the modern 2-watched literals scheme or the intermediate head/tail watchers. Ultimately a more effective watcher scheme would be interesting but not a significant priority seeing as most of the solver runtime is spent not in propagation but in problem translation. decision trees -------------- The new watchers produce slightly different decision trees, sometimes subtly changing solutions. Notably in various observed examples in Ubuntu 25.04, courier was installed as an MTA instead of postfix: The old decision tree was: apcupsd:amd64 -> mailutils:amd64=1:3.18-1 -> mailutils:amd64 -> postfix:amd64=3.9.1-10ubuntu1 The new decision tree is: lsb:amd64 -> lsb-core:amd64 -> courier-mta:amd64=1.3.13-1 The difference here being that lsb-core declares a mail-transport-agent dependency whereas mailutils depends on `default-mta | mail-transport-agency`; but both are effectively subject to selection at similar time. Further work is needed to optimize selection. A notable choice may also be to deal with broken packages like lsb-core that declare dependencies solely on a virtual package by reconstructing the default provider for that package utilizing default-* dependencies or similar notions. Likewise in the test suite, explanations are different in some uninstallable cases. backtracking ~~~~~~~~~~~~ The following major changes were observed in the 25.04 test suite: -tmp/regression-remove/07f0a068-36c2-11f0-b7c1-fa163e171f02:18 +tmp/regression-remove/07f0a068-36c2-11f0-b7c1-fa163e171f02:3 -tmp/regression-remove/32078f70-3734-11f0-a75a-fa163ec8ca8c:64 +tmp/regression-remove/32078f70-3734-11f0-a75a-fa163ec8ca8c:19 Other test cases showed little deviation, +/- 1, generally the same amount of backtracking. performance ~~~~~~~~~~~ Running Ubuntu's regression test suite resulted in no significant performance difference being observable. Before: 290s user time; 16.66% solver After: 299s user time; 17.36% solver Tests where run with make -j 8 and solver performance extracted perf report --symbol-filter=ResolveExternal --stdio

solver3: Rename decision to assignment

2026-01-05T21:20:24Z

The previous use of decision here conflicted with the use of decision level and the general notion of having made a decision, because the assignment might have been propagated as a matter of fact.

solver3: Sort dependency targets against current alternative

2025-08-26T11:41:35Z

Instead of inadvertently sorting dependency targets against the first alternative in an or group, sort them against the current alternative as we should. Otherwise we ended up sorting gnome-shell | notification-daemon With Package: notification-daemon Package: awesome Provides: notification-daemon into gnome-shell | awesome | notification-daemon <-we sorted this part wrongly-> This fixes a minor difference in test-release-candidate-switching in one case, but not the other where the difference was actually caused by the loss of install argument ordering information in the new solver, so just flip the arguments so both solvers produce the same outcome.

Evaluate and fall back to the 3.0 solver

2025-03-09T12:33:53Z

Always run the 3.0 solver after the internal solver. If the internal solver failed, and the 3.0 solver did not, use the 3.0 result. If 3.0 solver failed or produced a worse result than the internal solver, write an apport crash dump. We exclude situations which we now the solver can't handle, i.e. removals are forbidden and you requested removals, and stuff like that.

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: 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.

test: Fix 7 test cases for 3.0 solver, annotate others

2025-02-14T18:08:45Z

Fix the test cases we can fix directly; add annotations where we know what work is needed, next we'll look at the other bugs.

Give our test packages proper size information

2021-06-10T14:38:09Z

Temporary hacks should be temporary, especially if they hide bugs. After fixing one in the previous commit this is just busy work to add download information to the places which check that output. Gbp-Dch: Ignore

don't auto-switch candidate if installed is good enough

2017-12-13T22:52:07Z

If we perform candidate switching in requests like "apt install foo/bar" we should first check if the dependencies of foo from release bar are already satisfied by what is already installed before checking if the candidate (or switched candidate) would.

do not strip epochs from state version strings

2016-03-16T22:29:45Z

The epoch stripping in this code is done since day one, but in other places we show a version epochs are not stripped. If epochs are present in packages they tend to be an important information which we can't just drop and especially can't drop "sometimes" as that confuses users and tools alike – so even if removing code in use for (close to) 18 years feels wrong, it is probably the right choice for consistency. Closes: 818162