Sema: Score function conversions.

Break an ambiguity when overloads for e.g. [() -> ()] and [() throws -> ()] exist.

Author: jckarter

Diff for: lib/Sema/CSSimplify.cpp

@@ -913,6 +913,8 @@ ConstraintSystem::matchFunctionTypes(FunctionType *func1, FunctionType *func2,
 
   unsigned subFlags = flags | TMF_GenerateConstraints;
 
+  increaseScore(ScoreKind::SK_FunctionConversion);
+
   // Input types can be contravariant (or equal).
   SolutionKind result = matchTypes(func2->getInput(), func1->getInput(),
                                    subKind, subFlags,

Diff for: test/Constraints/collection-of-function.swift

@@ -0,0 +1,10 @@
+// RUN: %target-swift-frontend -parse -verify %s
+
+func foo(_:[() -> ()]){}
+func foo(_:[() throws -> ()]){}
+
+func x() {}
+
+var bs = [x]
+
+foo(bs)