swift234

Implement 'if let' and 'while let' statements.

Allow IfStmts and WhileStmts to have as their condition either an expression, as usual, or a pattern binding introduced by 'var' or 'let', which will conditionally bind to the value inside an optional. Unlike normal pattern bindings, these bindings require an in-line initializer, which will be required to be Optional type. Parse variable bindings in this position, and type-check them by requiring an Optional on the right-hand side and unwrapping it to form the pattern type. Extend SILGen's lowering of if and while statements to handle conditionally binding variables.

Swift SVN r13146