[5.0] Fix lookupDirect() use-after-scope bugs #20603
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In swiftlang#7530, NominalTypeDecl::lookupDirect() started returning TinyPtrVector instead of ArrayRef so that it wouldn’t be returning a pointer into a mutable data structure. Unfortunately, some callees assigned its return value into an ArrayRef; C++ happily converted the TinyPtrVector to an ArrayRef and then treated the TinyPtrVector as out-of-scope, so the ArrayRef would now point to an out-of-scope object. Oops.
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Cherry-picking the ASAN fix from #20557 to swift-5.0-branch.
@eeckstein We might close this without merging it since we're planning to branch again soon, but if not, we can push this PR forward.
In #7530, NominalTypeDecl::lookupDirect() started returning TinyPtrVector instead of ArrayRef. Unfortunately, some callees assigned its return value to a variable explicitly declared to be an ArrayRef; C++ happily converted the TinyPtrVector to an ArrayRef and then treated the TinyPtrVector as out-of-scope, so the ArrayRef would now point to an out-of-scope stack object.
This PR should fix ASan stack-use-after-scope test failures whose backtraces include one of:
There may still be other ASan failures after this PR. There should not be any normal test failures.
Resolves rdar://46031343.