Previously, whether a declaration is unavailable because it is obsolete was
determined based solely on the deployment target and not based on contextual
availability. Taking contextual availability into account makes availability
checking more internally consistent and allows library authors to evolve APIs
by obsoleting the previous declaration while introducing a new declaration in the
same version:
```
@available(macOS, obsoleted: 15)
func foo(_ x: Int) { }
@available(macOS, introduced: 15)
func foo(_ x: Int, y: Int = 0) { }
foo(42) // unambiguous, regardless of contextual version of macOS
```
This change primarily accepts more code that wasn't accepted previously, but it
could also be source breaking for some code that was previously allowed to use
obsoleted declarations in contexts that will always run on OS versions where
the declaration is obsolete. That code was clearly taking advantage of an
availabilty loophole, though, and in practice I don't expect it to be common.
Resolves rdar://144647964.
Get rid of the boolean arguments for unavailability in AvailabilityQuery's
constructors and introduce a `asUnavailable()` modifier that can be used
instead in the contexts where unavailability is relevant.
Use these queries to replace some duplicated code. Also, move the
`attr_inlinable_available.swift` test to the `Availability` sub-directory since
the test has more to do with availability checking than it has to do
specifically with the `@inlinable` attr.
Inverted availability queries were mis-compiled for zippered libraries because
the code that emits calls to `isOSVersionAtLeastOrVariantVersionAtLeast()` was
not updated when the `if #unavailable` syntax was introduced (at that time
support for zippered libraries had not yet been upstreamed). The result of
these calls is now inverted when appropriate.
To make it easier to manage the growing complexity of supporting availability
queries, Sema now models the relevant information about an availability query
with the new `AvailabilityQuery` type. It encapsulates the domain for the
query, the result if it is known at compile time, and the version tuple
arguments to pass to a runtime invocation if applicable.
Resolves rdar://147929876.
Expand the special-cased ASTWalker behavior for folded SequenceExprs
such that we always walk the folded expression when available. This
ensures that we don't attempt to add the same node multiple times
when expanding ASTScopes during pre-checking.
rdar://147751795
