swift234

Sema: Suppress explicit unavailability diagnostics in unavailable synthesized functions.

Suppress diagnostics about references to unavailable declarations when all
of the following conditions are met:

(1) the reference is in synthesized code;
(2) the reference is in a synthesized method; and
(3) the reference is inside a declaration marked as unavailable.

This, combined with prior work to infer availability annotations for synthesized
methods should eliminate the spurious diagnostics we have seen (e.g.,
rdar://problem/20154926) for references to unavailable types without the hammer
of suppressing all references to unavailable declarations in synthesized
functions. The right thing to do here is to not synthesize the bodies of these
functions in the first place. I've filed <rdar://problem/20491640> to track
this.

We will continue to emit an error for references to unavailable declarations
in non-implicit code, even if the reference is inside a declaration marked
unavailable.

Swift SVN r27197