6.0: [MoveOnly] Call borrowing methods on existentials. #73895
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It's a pass-through for FSPL's purposes.
Bail on non-consuming existential values which are move-only. Existential specialization requires creating a copy in such cases and that's illegal for move-only values.
rdar://125864434
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@swift-ci please test |
DougGregor
approved these changes
May 24, 2024
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@swift-ci please test macos platform |
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@swift-ci please test macos platform |
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Explanation: Fix a diagnostic-on-valid in the move-checker.
Previously, calling a borrowing method on a non-copyable existential failed with
error: usage of a noncopyable type that compiler can't verify. Here, this is fixed.The move-only address-checker relies on switching on opcodes to determine what part of a value is used by an instruction. It uses a bitmap consisting of atoms which can each be consumed at most once. An existential is a single "atom" from that perspective. Here, the
open_existential_addropcode is treated as a pass-through. This makes sense because it produces an instance of an archetype which is also an "atom", and it's "the same" "atom".Fixing the diagnostic exposed an issue in the existential specializer where it would create copies of non-copyable values when the argument was
@in_guaranteed. The existential specializer is fixed to bail out to avoid such illegal copies.Scope: Affects non-copyable code.
Issue: rdar://125864434
Original PR: #73857
Risk: Low. The fix is small and targeted.
Testing: Added regression test.
Reviewer: Andrew Trick ( @atrick )