Postfix operators can further be chained within an optional binding
chain, so we need to make sure they're handled in
`getMemberChainSubExpr`. Unresolved member chains still don't allow
them, so we need to add a new `kind` parameter to differentiate the
behavior here.
rdar://147826988
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
Since availability scopes may be built at arbitrary times, the builder may
encounter ASTs where SequenceExprs still exist and have not been folded, or it
may encounter folded SequenceExprs that have not been removed from the AST.
To avoid a double visit, track whether a SequenceExpr is folded and then
customize how ASTVisitor handles folded sequences.
Resolves rdar://142824799 and https://github.com/swiftlang/swift/issues/78567.
FunctionRefKind was originally designed to represent
the handling needed for argument labels on function
references, in which the unapplied and compound cases
are effectively the same. However it has since been
adopted in a bunch of other places where the
spelling of the function reference is entirely
orthogonal to the application level.
Split out the application level from the
"is compound" bit. Should be NFC. I've left some
FIXMEs for non-NFC changes that I'll address in a
follow-up.
