Doug Gregor ab576b31a7 Always supersede conformances implied by pre-macro-expansion conformances ...

Pre-macro-expansion conformances are introduced at the point where an
attached extension macro is attached to a particular nominal type, and
can imply other conformances. Once the macro is expanded, they are
expected to be replaced by the real conformance from the extension
produced by the macro. This includes any other conformances that are
implied by that conformances. Ensure that the real conformance---and
every conformances it implies---are considered "better" than the
pre-expansion conformances.

Fixes a bug where we would pick the wrong (pre-expansion)
conformances, which would then fail to get fully type-checked prior to
serialization. This could accept invalid code that then crashed the
compiler, as in rdar://112916159.

2023-08-20 09:27:38 -07:00

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