[REVERTED] Prune polymorphic implicits more aggressively#7067
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adriaanm merged 1 commit intoSep 7, 2018
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In rankImplicits, before we attempt to fully typecheck the pending candidate implicit, we first attempt to partially instantiate type variables in both the candidate and the target type and check for compatibility. If the compatibility check fails we can immediately prune the the candidate without having to fully typecheck it. In the kinds of implicit searches typical of the inductive style found in shapeless and related libraries this can result in a drastic reduction in the search space and a corresponding reduction in compile times. As an added bonus users of shapeless and shapeless based libraries which use shapeless's Lazy type will see benefits immediately without needing to wait for and port to byname implicit arguments.
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Rebased ... |
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Awesome 🙂 |
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@milessabin this regressed a usage of specs2, discovered while running the community build on 2.12.7: I confirmed that reverting this PR (and the undoLog changes from 6ea993a) makes it compile again. I'm not sure it's the same instance of the problem that you saw in the 2.13.x version. Thoughts? |
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Given how far past the 2.12.7 deadline we are, I decided to revert as much as needed to get the community build to go green. We'll have to save these improvements for 2.13 |
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This is a backport of #6580 targetting 2.12.7.
In
rankImplicits, before we attempt to fully typecheck the pending candidate implicit, we first attempt to partially instantiate type variables in both the candidate and the target type and check for compatibility. If the compatibility check fails we can immediately prune the the candidate without having to fully typecheck it.In the kinds of implicit searches typical of the inductive style found in shapeless and related libraries this can result in a drastic reduction in the search space and a corresponding reduction in compile
times.
As an added bonus users of shapeless and shapeless based libraries which use shapeless's
Lazytype will see benefits immediately without needing to wait for and port to byname implicit arguments.