Refactor cabal-install solver config log output

[erikd]

Includes:

• Apply some of @grayjay and @mpickering comments
• Fix Solver "rejecting" message is too verbose #4251

This is the PR #9541 rebased and fixed to build.

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[ulysses4ever]

Any chance you could add examples of what the new output looks like? Say, in the PR description.

[grayjay]

I haven't had a chance to look at the code yet, but, if I remember correctly, #9541 was a followup to #9159. Would it make sense to first update and merge #9159?

[Bodigrim]

This is going to break on boot package names like base-4.14.0.0/installed-4.14.0.0.

[erikd]

Yep, need to fix that.

[erikd]

@Bodigrim Can you give an example of it breaking on boot package names? The cabal-install:unit-tests tests have instances of names like that and the tests pass fine.

[mpickering]

Please implement the rendered using structured types. Taking shortcuts is how bugs manifest.

[erikd]

I haven't had a chance to look at the code yet, but, if I remember correctly, #9541 was a followup to #9159. Would it make sense to first update and merge #9159?

According to this comment this seems like a precursor to #9159 .

[grayjay]

According to this comment this seems like a precursor to #9159 .

The original change in #9159 was split into a refactoring change and a fix for #4251. Now the refactoring change is in #9159, and the fix for #4251 is in #9541. #9541 contains #9159, because the fix depends on the refactoring.

#9560 has also been merged since #9541 was written and helps address #4251. Do you know how this fix compares now?

[erikd]

Current version of this PR aims to minimize the differences in the cabal-install:unit-test output.

Still need to provide a information about how this version improves the solver output compared to the current output.

[erikd]

The changes between the output on master and the output in this PR is mostly incredibly minor (as shown by the tiny patch to the tests).

This is the only difference I could find in the cabal-install:unit-tests output:
master

      minimize conflict set with --minimize-conflict-set:                                                                              FAIL
        tests/UnitTests/Distribution/Solver/Modular/DSL/TestCaseUtils.hs:274:
        Unexpected error:
        Could not resolve dependencies:
        [__0] trying: A-3.0.0 (user goal)
        [__1] next goal: D (dependency of A)
        [__1] rejecting: D-1.0.0 (conflict: A => D==2.0.0)
        [__1] fail (backjumping, conflict set: A, D)
        After searching the rest of the dependency tree exhaustively, these were the goals I've had most trouble fulfilling: A (5), D (4)
        Use -p '/minimize conflict set with --minimize-conflict-set/' to rerun this test only.
      show original conflict set with --no-minimize-conflict-set:                                                                      FAIL
        tests/UnitTests/Distribution/Solver/Modular/DSL/TestCaseUtils.hs:274:
        Unexpected error:
        Could not resolve dependencies:
        [__0] trying: A-3.0.0 (user goal)
        [__1] next goal: B (dependency of A)
        [__1] rejecting: B-1.0.0 (conflict: A => B==2.0.0)
        [__1] fail (backjumping, conflict set: A, B)
        After searching the rest of the dependency tree exhaustively, these were the goals I've had most trouble fulfilling: A (7), B (2), C (2), D (2)
        Try running with --minimize-conflict-set to improve the error message.
        Use -p '/show original conflict set with --no-minimize-conflict-set/' to rerun this test only.

New:

      minimize conflict set with --minimize-conflict-set:                                                                              FAIL
        tests/UnitTests/Distribution/Solver/Modular/DSL/TestCaseUtils.hs:268:
        Unexpected solver log:
        targets: A
        constraints: 
          any.base installed (non-reinstallable package)
          any.ghc-bignum installed (non-reinstallable package)
          any.ghc-internal installed (non-reinstallable package)
          any.ghc-prim installed (non-reinstallable package)
          any.ghc installed (non-reinstallable package)
          any.integer-gmp installed (non-reinstallable package)
          any.integer-simple installed (non-reinstallable package)
          any.template-haskell installed (non-reinstallable package)
        preferences: 
        strategy: PreferLatestForSelected
        reorder goals: False
        count conflicts: True
        fine grained conflicts: True
        minimize conflict set: True
        independent goals: False
        avoid reinstalls: False
        shadow packages: False
        strong flags: False
        allow boot library installs: False
        only constrained packages: OnlyConstrainedNone
        max backjumps: infinite
        [__0] trying: A-3.0.0 (user goal)
        [__1] next goal: B (dependency of A)
        [__1] rejecting: B-1.0.0 (conflict: A => B==2.0.0)
        [__1] fail (backjumping, conflict set: A, B)
        [__0] trying: A-2.0.0
        [__1] trying: B-1.0.0 (dependency of A)
        [__2] next goal: C (dependency of A)
        [__2] rejecting: C-1.0.0 (conflict: A => C==2.0.0)
        [__2] fail (backjumping, conflict set: A, C)
        [__0] trying: A-1.0.0
        [__1] trying: B-1.0.0 (dependency of A)
        [__2] trying: C-1.0.0 (dependency of A)
        [__3] next goal: D (dependency of A)
        [__3] rejecting: D-1.0.0 (conflict: A => D==2.0.0)
        [__3] fail (backjumping, conflict set: A, D)
        [__0] fail (backjumping, conflict set: A, B, C, D)
        Found no solution after exhaustively searching the dependency tree. Rerunning the dependency solver to minimize the conflict set ({A, B, C, D}).
        Trying to remove variable "A" from the conflict set.
        [__0] trying: A-3.0.0 (user goal)
        [__1] next goal: B (dependency of A)
        [__1] rejecting: B-1.0.0 (conflict: A => B==2.0.0)
        [__1] fail (backjumping, conflict set: A, B)
        [__0] trying: A-2.0.0
        [__1] trying: B-1.0.0 (dependency of A)
        [__2] next goal: C (dependency of A)
        [__2] rejecting: C-1.0.0 (conflict: A => C==2.0.0)
        [__2] fail (backjumping, conflict set: A, C)
        [__0] trying: A-1.0.0
        [__1] trying: B-1.0.0 (dependency of A)
        [__2] trying: C-1.0.0 (dependency of A)
        [__3] next goal: D (dependency of A)
        [__3] rejecting: D-1.0.0 (conflict: A => D==2.0.0)
        [__3] fail (backjumping, conflict set: A, D)
        [__0] fail (backjumping, conflict set: A, B, C, D)
        Failed to remove "A" from the conflict set. Continuing with {A, B, C, D}.
        Trying to remove variable "B" from the conflict set.
        [__0] tryingE: A-3.0.0 (user goal)
        [__1] tryingE: C-1.0.0 (dependency of A)
        [__2] next goal: D (dependency of A)
        [__2] rejecting: D-1.0.0 (conflict: A => D==2.0.0)
        [__2] fail (backjumping, conflict set: A, D)
        [__0] skipping: A; 1.0.0, 2.0.0 (has the same characteristics that caused the previous version to fail: depends on 'D' but excludes version 1.0.0)
        [__0] fail (backjumping, conflict set: A, D)
        Successfully removed "B" from the conflict set. Continuing with {A, D}.
        Trying to remove variable "D" from the conflict set.
        [__0] trying: A-3.0.0 (user goal)
        [__1] next goal: D (dependency of A)
        [__1] rejecting: D-1.0.0 (conflict: A => D==2.0.0)
        [__1] fail (backjumping, conflict set: A, D)
        [__0] skipping: A; 1.0.0, 2.0.0 (has the same characteristics that caused the previous version to fail: depends on 'D' but excludes version 1.0.0)
        [__0] fail (backjumping, conflict set: A, D)
        Failed to remove "D" from the conflict set. Continuing with {A, D}.

I suppose the main benefit of this PR is that in the file cabal-install-solver/src/Distribution/Solver/Modular/Message.hs detection of errors is separated from reporting of errors.

[erikd]

I haven't had a chance to look at the code yet, but, if I remember correctly, #9541 was a followup to #9159. Would it make sense to first update and merge #9159?

I have had a look at #9159 (against master from 18 months ago) but its rather difficult what really changes between them. I am studying #9159 more closely to figure out what it actually does.

Update: I am not able find any significant differences between the behavior of the code in this PR and in #9541 .

[grayjay]

Update: I am not able find any significant differences between the behavior of the code in this PR and in #9541 .

Isn't this PR an updated version of #9541? Do you mean #9560?