Avoid leaking constraints in typer states #12333
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owningState weak reference can be reset to null. This was observed when compiling scalatest.
When we replace a type lambda in a constraint by another, the type variables associated with the old lambda changed their origin to point to the new lambda. But that means that the same type variables in predecessor typestates do not point to their associated lambda anymore. To fix this, we have to do the same renaming of type lambdas also in predecessor typestates.
I verified that with the previous commit all compilation tests except two neg tests pass this check.
Besides the constraint, we also need to reset any instantiated type variables. This is necessary for correctness and also to avoid uncollected garbage in constraints when an entry is never dropped since the associated type variables are no longer owned by the constraint.
It is not enough to reset the constraint only, since type variables might have gotten instantiated during matchtype reduction. With that change we now test in -Ycheck that constraints are empty after each phase.
odersky
changed the title
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test performance please |
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performance test scheduled: 1 job(s) in queue, 1 running. |
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I also ran the scalatest, stdlib213, and shapeless builds from CB. The maximal constraint was in each case smaller than 30 entries. |
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Performance test finished successfully: Visit https://dotty-bench.epfl.ch/12333/ to see the changes. Benchmarks is based on merging with master (69c800b) |
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The set of fixes here together makes sure that the constraint of the typerstate at the end of each phase is empty. This is now tested under -Ycheck.