Now that Array and Dictionary conform to Hashable, we need to make sure that their bridged counterparts provide the same hash values when converted to AnyHashable.
NSString has a stricter concept of equality than Swift’s String, so it is possible to construct NSDictionary/NSSet instances that contain duplicate keys according to Swift’s definition of string equality. This change improves how we handle these cases by coalescing the duplicate keys (keeping a single value).
rdar://problem/35995647
This avoids indirection by making calls directly to the C implementations which prevents potentials of mismatched intent or changes of calling convention of @_silgen. The added benefit is that all of the shims in this case are no longer visible symbols (anyone using them was not authorized out side of the Foundation overlay). Also the callout methods in the headers now all share similar naming shcemes for easier refactoring and searching in the style of __NS<class><action> style. The previous compiled C/Objective-C source files were built with MRR the new headers MUST be ARC by Swift import rules.
The one caveat is that certain functions MUST avoid the bridge case (since they are part of the bridging code-paths and that would incur a recursive potential) which have the types erased up to NSObject * via the macro NS_NON_BRIDGED.
The remaining @_silgen declarations are either swift functions exposed externally to the rest of Swift’s runtime or are included in NSNumber.gyb which the Foundation team has other plans for removing those @_silgen functions at a later date and Data.swift has one external function left with @_silgen which is blocked by a bug in the compiler which seems to improperly import that particular method as an inline c function.
* replace unused closure parameters with '_' in stdlib source
* fold some _ closure arguments into line above
* fold more _ closure arguments into line above
