We used to diagnose references to unavailable declarations in
two places:
- inside Exprs, right after type checking the expression
- inside TypeReprs, from resolveType()
In broad terms, resolveType() is called with TypeReprs
stored inside both Stmts and Decls.
To handle the first case, I added a new overload of
diagAvailability() that takes a Stmt, to be called from
typeCheckStmt(). This doesn't actually walk into any Exprs
stored inside the statement; this means it only walks
Patterns and such.
For the second case, a new DeclAvailabilityChecker is
now defined in TypeCheckAccess.cpp. It's structure is
analogous to the other three walkers there:
- AccessControlChecker
- UsableFromInlineChecker
- ExportabilityChecker
The new implementation of availability checking for types
introduces a lot more code than the old online logic
it replaces. However, I hope to consolidate some of the
code duplication among the four checkers that are defined
in TypeCheckAccess.cpp, and do some other cleanups that
will make the benefit of the new approach apparent.
CharacterView is now entirely redundant in Swift 4. Deprecate its
use. This also allows us to schedule the unbreaking of
String.CharacterView leakiness without a hard source break.
Collection's popFirst is only present when the Collection is its own
SubSequence type. String and String's views are no longer their own
SubSequenes, so popFirst is no longer present. Unfortunately, this
breaks code in swift-version 3 and it also gives a terrible diagnostic
to users. This change introduces an implementation for swift-version 3
mode and better diagnostics for Swift 4 code. Tests included.
