Remove the package instance from D.Solver.Modular.Var (closes #4142).
This change has several effects: - The solver no longer includes the package version in messages that relate to a package's flags, stanzas, or dependencies. However, the solver always chooses the package version before choosing any flags, stanzas, or dependencies for the package, so it should be easy to find the version by looking earlier in the log. - In conflict counting, the solver treats flags with the same name in different versions of a package as the same flag. This change in the conflict counting heuristic can improve the solver's efficiency when the same flag causes the same conflicts in different versions of a package. The same applies to enabling tests or benchmarks. - Each flag or stanza can only appear once in a conflict set. This has no effect on behavior, but it simplifies the message containing the final conflict set. Here is an example of the change in a log message. It only prints hackage-server's version once, when it first chooses the package. The conflict set also has one fewer variable, but that is probably due to the change in conflict counting. Resolving dependencies... cabal: Could not resolve dependencies: trying: hackage-server-0.5.0 (user goal) -trying: hackage-server-0.5.0:+build-hackage-build -trying: unix-22.214.171.124/installed-2.7... (dependency of hackage-server-0.5.0 +trying: hackage-server:+build-hackage-build +trying: unix-126.96.36.199/installed-2.7... (dependency of hackage-server +build-hackage-build) -next goal: aeson (dependency of hackage-server-0.5.0 +build-hackage-build) +next goal: aeson (dependency of hackage-server +build-hackage-build) rejecting: aeson-188.8.131.52, aeson-184.108.40.206, aeson-220.127.116.11, aeson-18.104.22.168, aeson-22.214.171.124, aeson-126.96.36.199, aeson-188.8.131.52, aeson-184.108.40.206, aeson-220.127.116.11, aeson-18.104.22.168, aeson-0.11.3.0, aeson-0.11.2.1, aeson-0.11.2.0, aeson-0.11.1.4, aeson-0.11.1.3, aeson-0.11.1.2, aeson-0.11.1.1, aeson-0.11.1.0, aeson-0.11.0.0, aeson-0.9.0.1, aeson-0.9.0.0, aeson-0.8.1.1, aeson-0.8.1.0, aeson-0.8.0.2, aeson-0.7.0.6, aeson-0.7.0.4, aeson-0.6.2.1, aeson-0.6.2.0 (conflict: hackage-server +build-hackage-build => aeson==0.6.1.*) rejecting: aeson-0.6.1.0 (conflict: unix => time==22.214.171.124/installed-1.6..., aeson => time<1.5) rejecting: aeson-0.6.0.2, aeson-0.6.0.1, aeson-0.6.0.0, aeson-0.5.0.0, aeson-0.4.0.1, aeson-0.4.0.0, aeson-0.3.2.14, aeson-0.3.2.13, aeson-0.3.2.12, aeson-0.3.2.11, aeson-0.3.2.10, aeson-0.3.2.9, aeson-0.3.2.8, aeson-0.3.2.7, aeson-0.3.2.6, aeson-0.3.2.5, aeson-0.3.2.4, aeson-0.3.2.3, aeson-0.3.2.2, aeson-0.3.2.1, aeson-0.3.2.0, aeson-0.3.1.1, aeson-0.3.1.0, aeson-0.3.0.0, aeson-0.2.0.0, aeson-0.1.0.0, aeson-0.10.0.0, aeson-0.8.0.1, aeson-0.8.0.0, aeson-0.7.0.5, aeson-0.7.0.3, aeson-0.7.0.2, aeson-0.7.0.1, aeson-0.7.0.0 (conflict: hackage-server +build-hackage-build => aeson==0.6.1.*) After searching the rest of the dependency tree exhaustively, these were the -goals I've had most trouble fulfilling: aeson, hackage-server, -hackage-server-0.5.0:build-hackage-build, -hackage-server-0.4:build-hackage-mirror, template-haskell +goals I've had most trouble fulfilling: aeson, +hackage-server:build-hackage-build, hackage-server, template-haskell I ran hackage-benchmark to compare this commit with master (two commits earlier). I used --min-run-time-percentage-difference-to-rerun=10 to only rerun packages if the run times differed by more than 10% in the first trial, and defaults for the rest of the options (10 trials, p-value of 0.05, 90 second timeout). The index state was "2017-09-24T03:35:06Z". 1 is master, and 2 is this commit: package result1 result2 mean1 mean2 stddev1 stddev2 speedup CC-delcont-ref Solution Solution 1.467s 1.505s 0.019s 0.100s 0.975 ascii-cows Solution Solution 1.827s 1.758s 0.159s 0.012s 1.040 opaleye-classy NoInstallPlan NoInstallPlan 4.588s 4.070s 0.043s 0.032s 1.127 range-space NoInstallPlan NoInstallPlan 2.642s 2.299s 0.016s 0.016s 1.149 rts PkgNotFound PkgNotFound 1.323s 1.327s 0.032s 0.033s 0.997 servant-auth-docs Solution Solution 1.968s 1.998s 0.017s 0.074s 0.985 thorn BackjumpLimit NoInstallPlan 4.793s 3.141s 0.050s 0.034s 1.526 unordered-intmap Solution Solution 1.502s 1.511s 0.081s 0.047s 0.994 I looked at the solver logs for the three packages with the largest changes in run time, opaleye-classy, range-space, and thorn. Each one showed that the solver started preferring a flag in an older version of a package after it had caused conflicts in a newer version of the package.