Nested calls to importBaseMemberDecl() subvert its cache and compromise its idempotence, causing the semantic checker to spuriously report ambiguous member lookups when multiple ClangRecordMemberLookup requests are made (e.g., because of an unrelated missing member lookup).
One such scenario is documented as a test case: test/Interop/Cxx/class/inheritance/inherited-lookup-typechecker.swift fails without this patch because of the expected error from the missing member. Meanwhile, test/Interop/Cxx/class/inheritance/inherited-lookup-executable.swift works because it does not attempt to access a missing member.
This patch fixes the issue by only calling importBaseMemberDecl() in the most derived class (where the ClangRecordMemberLookup originated, i.e., not in recursive requests).
As a consequence of my patch, synthesized member accessors in the derived class directly invoke the member from the base class where the member is inherited from, rather than incurring an indirection at each level of inheritance. As such, the synthesized symbol names are different (and shorter). I've taken this opportunity to update the relevant tests to // CHECK for more of the mangled symbol, rather than only the synthesized symbol prefix, for more precise testing and slightly better readability.
rdar://141069984
This test does not produce consistent SIL across various test
configurations. We have a discrepancy on whether an argument is
@in_guaranteed vs. @guaranteed.
Tracked in rdar://128424443.
We haven't yet solved the underlying issue in rdar://128013193 and the
workaround to make it conditionally use the better importing strategy of
Unsafe{Mutable}Pointer no longer will apply, since NoncopyableGenerics
is here.
