Add test case for backjumping when dependencies are not linked

[grayjay]

This is another test for the issue described in #3327. The previous test started passing after #3221 was merged. I found this test case with QuickCheck and tried to clean it up, but, unfortunately, it's still messy. The failure only occurs with a specific goal order.

The solver must backtrack to avoid linking 1.D. However, none of the conflict sets at level 6 contain 1.D. 1.D should be added on the line with the message "dependencies not linked".

targets: C, A, B
constraints:
  stanzas A test (unknown source)
  stanzas B test (unknown source)
  stanzas C test (unknown source)
  stanzas D test (unknown source)
  stanzas D test (unknown source)
preferences:
strategy: PreferLatestForSelected
reorder goals: False
independent goals: True
avoid reinstalls: False
shadow packages: False
strong flags: False
max backjumps: infinite
[__0] trying: 0.C-1.0.0 (user goal)
[__1] trying: 0.D-2.0.0 (dependency of 0.C-1.0.0)
[__2] trying: 1.A-1.0.0 (user goal)
[__3] trying: 1.B-1.0.0 (dependency of 1.A-1.0.0)
[__4] trying: 1.D~>0.D-2.0.0 (dependency of 1.B-1.0.0)
[__5] trying: 2.B~>1.B-1.0.0 (user goal)
[__6] trying: 2.D~>1.D-2.0.0 (dependency of 2.B-1.0.0)
[__7] rejecting: 2.B-1.0.0:!test (constraint from unknown source requires opposite flag selection)
[__7] rejecting: 2.B-1.0.0:*test (conflict: 2.D==2.0.0, 2.B-1.0.0:test => 2.D==1.0.0)
[__7] fail (backjumping, conflict set: 2.B, 2.D, 2.B-1.0.0:test)
[__6] trying: 2.D~>0.D-2.0.0
[__7] rejecting: 2.B-1.0.0:!test (constraint from unknown source requires opposite flag selection)
[__7] rejecting: 2.B-1.0.0:*test (conflict: 2.D==2.0.0, 2.B-1.0.0:test => 2.D==1.0.0)
[__7] fail (backjumping, conflict set: 2.B, 2.D, 2.B-1.0.0:test)
[__6] rejecting: 2.D-2.0.0 (multiple instances; conflict set: 0.C, 0.D, 2.B, 2.D)
[__6] rejecting: 2.D-1.0.0 (dependencies not linked: cannot make 2.D canonical member of {*0.D-2.0.0,1.D-2.0.0,2.D-2.0.0}; conflict set: 2.B, 2.D)
[__6] fail (backjumping, conflict set: 0.C, 0.D, 2.B, 2.D, 2.B-1.0.0:test)
[__5] rejecting: 2.B-1.0.0 (multiple instances; conflict set: 1.A, 1.B, 2.B)
[__2] fail (backjumping, conflict set: 0.C, 0.D, 1.A, 1.B, 2.B, 2.D, 2.B-1.0.0:test)
[__1] rejecting: 0.D-1.0.0 (conflict: 0.C => 0.D==2.0.0)
[__0] fail (backjumping, conflict set: 0.C, 0.D, 1.A, 1.B, 2.B, 2.D, 2.B-1.0.0:test)
Unit Tests
  UnitTests.Distribution.Client.Dependency.Modular.Solver
    Independent goals
      indepGoals4: FAIL (expected)
        Unexpected error:
        Could not resolve dependencies:
        trying: 2.B~>1.B-1.0.0 (user goal)
        trying: 2.D~>1.D-2.0.0 (dependency of 2.B-1.0.0)
        rejecting: 2.B-1.0.0:!test (constraint from unknown source requires opposite flag selection)
        rejecting: 2.B-1.0.0:*test (conflict: 2.D==2.0.0, 2.B-1.0.0:test => 2.D==1.0.0)
        Dependency tree exhaustively searched.
        (expected failure)

[edsko]

Great! Thanks.

[kosmikus]

Yes, thanks a lot.