This fixes l-value computation in buildStorageReference when composing property
wrappers.
The l-value-ness required for each instance in a property wrapper chain is
computed through a request and returned as an instance of
PropertyWrapperLValueness.
wrapped value placeholder in an init(wrappedValue:) call that was previously
injected as an OpaqueValueExpr. This commit also restores the old design of
OpaqueValueExpr.
wrapper original wrapped value expression inside of CSApply.
This prevents type checking the synthesized backing storage initializer
twice - once with the original expression and again with the placeholder.
If the 'wrappedValue:' parameter is an escaping autoclosure, and a
struct property is marked with that property wrapper, the memberwise
initializer of the struct is now synthesized with an escaping
autoclosure for that property.
Fixes rdar://problem/53407949 | SR-11138. Previously, we'd only look at the outermost property wrapper to decide whether the wrapped property's getter and setter were `mutating` (or exist at all). In reality, this requires considering the semantics of the composed accesses of each wrapper layer's
`wrappedValue` property. Fixing this systematically addresses a number of issues:
- As SR-11138 reported, composing a nonmutating-get-set wrapper ought to produce a composed wrapper
that's nonmutating.
- We would previously allow a property wrapper with a mutating getter to be nested inside one with
only a getter, even though the resulting implementation was unsound (because there's no mutable
context for the inner wrapper to execute its get on.)
- Similarly, we would construct unsound setters in cases where the setter can't exist, such as when
the nested wrapper isn't settable but the outer wrapper is.
Extend handling of enclosing-self subscripts by differentiating
between the original wrapped property (which now goes through
`subscript(_enclosingInstance:wrapped:storage:)`) and the projected
property (which goes through
`subscript(_enclosingInstance:projected:storage:)`). The new middle
argument provides a key path to the property that was accessed,
allowing one to distinguish the property being updated.
