Fix default witness checking [4.1] #13365
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Otherwise, we'll never get a chance to drain the TypeChecker's UsedConformances list. Fixes <https://bugs.swift.org/browse/SR-6565>, <rdar://problem/35949729>.
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@swift-ci Please test |
slavapestov
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Description: Fixes a type checker bug where SILGen would try to use an incomplete conformance due to a subtle phase ordering issue. Since the problem was with default witness tables and those are not used unless building a resilient module, go further and don't emit them at all unless resilience is enabled.
Scope of the issue: Reported by a user on Twitter who was hitting this with a real project.
Risk: Low, we're basically just disabling a code path for normal users.
Origination: Probably the specific crash was introduced in 4.0 when conformance access paths came along. Default witness tables have been broken in this way since first added in 3.0 or 3.1.
Tested: New test case added.
Radar: rdar://problem/35949729
Reviewed by: @jckarter