[ConstraintSystem] Avoid recording duplicate fixes for contextual type mismatch

Author: xedin

lib/Sema/CSSimplify.cpp

@@ -3877,6 +3877,11 @@ bool ConstraintSystem::repairFailures(
     if (lhs->isTypeVariableOrMember() || rhs->isTypeVariableOrMember())
       break;
 
+    // If there is already a fix for contextual failure, let's not
+    // record a duplicate one.
+    if (hasFixFor(getConstraintLocator(locator)))
+      return true;
+
     auto purpose = getContextualTypePurpose(anchor);
     if (rhs->isVoid() &&
         (purpose == CTP_ReturnStmt || purpose == CTP_ReturnSingleExpr)) {