[6.0][Conformance] Always downgrade redundant conformances to marker protocols to a warning. #75426
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…cols to a warning. Previous compiler versions allowed this, so we should stage the change in as a warning. This was already a warning across modules, so this change only impacts redundant conformances to marker protocols within a module. This code also isn't particularly harmful, because marker protocols don't have requirements, so there isn't the same risk of unexpected behavior as other redundant conformances. (cherry picked from commit 5eb16ad)
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@swift-ci please test |
DougGregor
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Jul 23, 2024
(cherry picked from commit 286bdeb)
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Explanation: Compiler versions <= 6.0 allowed redundant conformances to marker protocols within the same module. To diagnose attempts to change the un-availability of a conformance to
Sendable, [6.0][ConformanceLookup] Don't allow skipping inherited unavailable conformances in favor of explicit available ones. #75223 made a change to not allow superseding marker protocol conformances, which inadvertently broke cases where a redundant conformance toCopyablewas written within a module.To avoid a source break, this change downgrades redundant conformances to marker protocols to warnings always. This code also isn't particularly harmful, because marker protocols don't have requirements, so there isn't the same risk of unexpected behavior as other redundant conformances. There's no particular need for this diagnostic to be an error.
Scope: Only impacts redundant conformances to marker protocols within the same module.
Issues: rdar://132346903
Original PRs: [Conformance] Always downgrade redundant conformances to marker protocols to a warning. #75425
Risk: Low; this change only opts more cases into the "downgrade to warning" path for redundant conformance diagnostics. Specifically, it replaces a check for
Sendableto a check that the protocol is a marker protocol.Testing: Added a new test case.
Reviewers: @DougGregor