[Constraint] Disable "fixed" overload choice by default

Author: xedin

lib/Sema/Constraint.cpp

@@ -169,7 +169,7 @@ Constraint::Constraint(Type type, OverloadChoice choice, DeclContext *useDC,
                        ConstraintFix *fix, ConstraintLocator *locator,
                        ArrayRef<TypeVariableType *> typeVars)
     : Kind(ConstraintKind::BindOverload), TheFix(fix), HasRestriction(false),
-      IsActive(false), IsDisabled(false), RememberChoice(false),
+      IsActive(false), IsDisabled(bool(fix)), RememberChoice(false),
       IsFavored(false),
       NumTypeVariables(typeVars.size()), Overload{type, choice, useDC},
       Locator(locator) {

lib/Sema/Constraint.h

@@ -401,6 +401,7 @@ class Constraint final : public llvm::ilist_node<Constraint>,
                                  ConstraintLocator *locator);
 
   /// Create a bind overload choice with a fix.
+  /// Note: This constraint is going to be disabled by default.
   static Constraint *createFixedChoice(ConstraintSystem &cs, Type type,
                                        OverloadChoice choice,
                                        DeclContext *useDC, ConstraintFix *fix,