[Diagnostics] Add a tailored fix when ternary is associated with return

If it has been detected that there is an attempt to return a value
from a function without result type, let's diagnose that specifically
in cases when ternary operator is involved.

Author: xedin

lib/Sema/CSSimplify.cpp

@@ -4224,6 +4224,12 @@ bool ConstraintSystem::repairFailures(
         if (hasFixFor(loc, FixKind::ContextualMismatch))
           return true;
 
+        if (contextualType->isVoid() &&
+            getContextualTypePurpose(anchor) == CTP_ReturnStmt) {
+          conversionsOrFixes.push_back(RemoveReturn::create(*this, lhs, loc));
+          break;
+        }
+
         conversionsOrFixes.push_back(
             ContextualMismatch::create(*this, lhs, rhs, loc));
         break;

test/Constraints/diagnostics.swift

@@ -207,7 +207,7 @@ func r17020197(_ x : Int?, y : Int) {
 
 // <rdar://problem/20714480> QoI: Boolean expr not treated as Bool type when function return type is different
 func validateSaveButton(_ text: String) {
-  return (text.count > 0) ? true : false  // expected-error {{unexpected non-void return value in void function}}
+  return (text.count > 0) ? true : false  // expected-error {{unexpected non-void return value in void function}} expected-note {{did you mean to add a return type?}}
 }
 
 // <rdar://problem/20201968> QoI: poor diagnostic when calling a class method via a metatype