Sema: Ban references to protocol extension members with opaque result types on an existential base #34499
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… types on an existential base The substituted type of the member reference is an OpaqueTypeArchetypeType whose substitution map sends Self to the opened existential type for the base value. Sema erases opened existential types to their upper bound, but this is not a valid transformation in this case, because the 'Self' type reference is invariant. Calling this member on two different existential values would produce the same erased type, but this is wrong, because it actually depends on the concrete type stored in the existential. Fixes <https://bugs.swift.org/browse/SR-13419>, <rdar://problem/67451810>.
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The substituted type of the member reference is an OpaqueTypeArchetypeType
whose substitution map sends Self to the opened existential type for the
base value. Sema erases opened existential types to their upper bound, but
this is not a valid transformation in this case, because the 'Self' type
reference is invariant. Calling this member on two different existential
values would produce the same erased type, but this is wrong, because
it actually depends on the concrete type stored in the existential.
Fixes https://bugs.swift.org/browse/SR-13419, rdar://problem/67451810.