Fixed issue with amibguity error with partialApply function.

Author: kavon

include/swift/Sema/CSFix.h

@@ -2032,6 +2032,10 @@ class MustBeCopyable final : public ConstraintFix {
 
   bool diagnose(const Solution &solution, bool asNote = false) const override;
 
+  bool diagnoseForAmbiguity(CommonFixesArray commonFixes) const override {
+    return diagnose(*commonFixes.front().first);
+  }
+
   static MustBeCopyable *create(ConstraintSystem &cs,
                              Type noncopyableTy,
                              ConstraintLocator *locator);

lib/Sema/CSSimplify.cpp

@@ -4201,7 +4201,7 @@ ConstraintSystem::matchTypesBindTypeVar(
     }
   }
 
-  // If the type variable cannot bind to a move-only type, fail.
+  // If the type variable can't bind to a move-only type, diagnose and fail.
   if (!typeVar->getImpl().canBindToMoveOnly() && type->isPureMoveOnly()) {
     if (shouldAttemptFixes()) {
       auto *fix = MustBeCopyable::create(*this, type,