Immediately before invoking the ObjC API, get the current continuation, capture it into a block to
pass as the completion handler, and then await the continuation, whose resume/error successors
serve as the semantic return/throw result of the call. This should complete the caller-side part
of SILGen; the completion handler block implementation is however still only a stub.
I am going to be cleaning up some of the code here so that I can move the
creation of a temporary needed for foreign error handling earlier and move the
handling of the error parameter in general into ResultPlanBuilder.
Otherwise, the temporary is cleaned up when I pop a soon to be committed patch
that creates scopes around call sites.
rdar://30955427
ResultPlan and related constructs have already been written in a type erased
fashion. This commit takes advantage of this by moving the details of the code
to ResultPlan.{cpp,h}.
This slims down SILGenApply.cpp in a NFC way and ensures that other code in
SILGenApply can not depend on the details of ResultPlan. Also it is my hope that
this can become the beginning of the merging of the ResultPlan from SILGenApply
and from SILGenPoly. We should only have 1 way in SILGen to build applies and
create apply results.
rdar://29791263
