swift234

reapply r22223 with a testcase update:

Dramatically improve DI diagnostics in initializers fixing rdar://18414728.

As one small example of the improvement, where an initializer like this:

class Foo {
    var path:String? {
        return "boo"
    }
    
    let aaaaa:String
    
    init() {
        if let p1 = path {

used to  produce the error: "error: variable 'self.aaaaa' used before being initialized" on path,
we now produce:

x.swift:9:21: error: use of 'self' in property access 'path' before all stored properties are initialized
        if let p1 = path {
                    ^
x.swift:6:9: note: 'self.aaaaa' not initialized
    let aaaaa:String
        ^

which is more useful.





Swift SVN r22238