Avoid infinite loop in type variable instantiation #9030
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test performance please |
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performance test scheduled: 1 job(s) in queue, 0 running. |
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Performance test finished successfully: Visit http://dotty-bench.epfl.ch/9030/ to see the changes. Benchmarks is based on merging with master (59587ba) |
Rename `checkNonCyclic` to `occursAtToplevel` and refactor it to return a boolean, use it in `ConstraintHandling#instanceType` to make sure we do not introduce a cycle when instantiating a type variable. Some alternatives I considered: - Run `widenInferred` inside frozen constraints: this prevents `Set[A] | Set[Int]` to be widened to `Set[Int]` after instantiating `A := Int` - Run `widenInferred` with the upper bound of `param` instead of `param` itself as a bound: I think this is still not safe because the upper bound of `param` might recursively refer to `param`, it also breaks type inference of one expression in ZIO.
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Rename
checkNonCyclictooccursAtTopleveland refactor it to returna boolean, use it in
ConstraintHandling#instanceTypeto make sure wedo not introduce a cycle when instantiating a type variable.
Some alternatives I considered:
widenInferredinside frozen constraints: this preventsSet[A] | Set[Int]to be widened toSet[Int]after instantiatingA := IntwidenInferredwith the upper bound ofparaminstead ofparamitself as a bound: I think this is still not safe because the upper
bound of
parammight recursively refer toparam, it also breakstype inference of one expression in ZIO.