Slava Pestov 18f216c581 Sema: Fix re-entrant call to ensureRequirementsAreSatisfied() when resolving associated conformances ...

ConformanceChecker::ensureRequirementsAreSatisfied() modifies the
conformance as it resolves each one of its associated conformances,
so a re-entrant call can end up corrupting state by adding too
many elements to the buffer, or adding elements at the wrong
offsets.

If TypeChecker::checkConformanceRequirements() was called before
ConformanceChecker::resolveTypeWitnesses(), we could re-entrantly call
ConformanceChecker::ensureRequirementsAreSatisfied():

TypeChecker::checkConformanceRequirements()
=> ConformanceChecker::ensureRequirementsAreSatisfied()
   => Type::subst(), etc
      => ConformanceChecker::resolveTypeWitnesses()
         => ConformanceChecker::ensureRequirementsAreSatisfied()

The code in SubstitutionMap::lookupConformance() worked around
this by checking the failure condition and calling
resolveTypeWitness() first, before calling getAssociatedConformance().

Instead, remove this and call resolveTypeWitness() from inside
NormalProtocolConformance::getAssociatedConformance().

2019-05-28 22:08:31 -04:00

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