[Type checker] Downgrade some "redundant conformance" errors to warnings. #9160
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A cross-reference in a module cannot refer to a parsed entity, because the parsed entity couldn’t have been seen when the module was built. Filter these out, which prevents a crash in the subsequent commit. (cherry picked from commit 905b6b1)
…ngs. When an extension introduces a conformance that already exists, the type checker will reject the conformance and then ignore it. In cases where the original conformance is in the same module as the type or protocol (but the new, redundant conformance is in some other module), downgrade this error to a warning. This helps with library-evolution cases where a library omitted a particular conformance for one of its own types/protocols in a previous version, then introduces it in a new version. The specific driver for this is the conformance of String to Collection, which affects source compatibility. Fixes rdar://problem/31104415. (cherry picked from commit f7bccb0)
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@swift-ci please test |
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@swift-ci please clean test Linux |
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When an extension introduces a conformance that already exists, the
type checker will reject the conformance and then ignore it. In cases
where the original conformance is in the same module as the type or
protocol (but the new, redundant conformance is in some other module),
downgrade this error to a warning. This helps with library-evolution
cases where a library omitted a particular conformance for one of its
own types/protocols in a previous version, then introduces it in a new
version.
The specific driver for this is the conformance of String to
Collection, which affects source compatibility. Fixes
rdar://problem/31104415.