The `_SwiftConcurrencyShims` module was imported `@_implementationOnly` which
was causing warnings to be emitted during the stdlib build. The module
currently serves no purpose; the only declaration it contains is a defunct
`_SwiftContext` struct which is not referenced by anything. The module needs to
continue to exist for source compatibility, though, since it is part of the
toolchain and imported publicly from other modules.
Supported older compilers don't enable this feature by default, so it can't be
omitted from the `_Concurrency` module's flags (regression from
https://github.com/swiftlang/swift/pull/74543).
Additionally, remove `@_allowFeatureSuppression(IsolatedAny)` from all
declarations. We no longer need to support compilers that don't have the
`IsolatedAny` feature, so the suppression is superfluous and the alternative
branches didn't actually build anyways. _Additionally_, the suppressible
feature logic could not handle suppressing `IsolatedAny` simultaneously with
`SendingArgsAndResults`, resulting in a broken interface because `sending` was
used outside `#if $SendingArgsAndResults` guards.
While the new parameter is added in a compatible way where code which
does not refer to it will get a defaulted nil value; since we refer to a
new parameter name in source, we need to guard it with a language
feature -- as old compilers will not have this new name available.
This should prevent a potential condfail issue.
Concurrency runtime expects discarding task operation entrypoint
function not to have result type, but the current SILGen
implementation generates reabstraction thunk to convert `() -> Void`
to `() -> T` for the operation function.
Since the `T` is always `Void` for DiscardingTG, the mismatch of result
type expectation does not cause any problem on most platforms, but the
signature mismatch causes a problem on WebAssembly.
This patch introduces new builtin operations for creating discarding
task, which always takes `() -> Void` as the operation function type.
