PrintAsClang is supposed to emit declarations in the same order regardless of the compiler’s internal state, but we have repeatedly found that our current criteria are inadequate, resulting in non-functionality-affecting changes to generated header content. Add a diagnostic that’s emitted when this happens soliciting a bug report.
Since there *should* be no cases where the compiler fails to order declarations, this diagnostic is never actually emitted. Instead, we test this change by enabling `-verify` on nearly all PrintAsClang tests to make sure they are unaffected.
This did demonstrate a missing criterion that only mattered in C++ mode: extensions that varied only in their generic signature were not sorted stably. Add a sort criterion for this.
Use the `%target-swift-5.1-abi-triple` substitution to compile the tests for
deployment to the minimum OS versions required for use of _Concurrency APIs,
instead of disabling availability checking.
When we printed `async` methods, we did not print a nullability annotation on the `completionHandler` parameter. This commit adds `_Nonnull`, which matches the generated SIL.
Fixes rdar://80989714.
@objc async declarations are mapping into completion-handler-based
methods in Objective-C, so ensure that the result type, parameters,
and attributes reflect that.
