[CSFix] Add a skeleton of weak pattern with non-optional type fix

Author: xedin

include/swift/Sema/CSFix.h

@@ -331,7 +331,10 @@ enum class FixKind : uint8_t {
 
   /// Specify a type for an explicitly written placeholder that could not be
   /// resolved.
-  SpecifyTypeForPlaceholder
+  SpecifyTypeForPlaceholder,
+
+  /// Allow `weak` declarations to be bound to a non-optional type.
+  AllowNonOptionalWeak,
 };
 
 class ConstraintFix {
@@ -2424,6 +2427,21 @@ class AllowInvalidStaticMemberRefOnProtocolMetatype final
   create(ConstraintSystem &cs, ConstraintLocator *locator);
 };
 
+class AllowNonOptionalWeak final : public ConstraintFix {
+  AllowNonOptionalWeak(ConstraintSystem &cs, ConstraintLocator *locator)
+      : ConstraintFix(cs, FixKind::AllowNonOptionalWeak, locator) {}
+
+public:
+  std::string getName() const override {
+    return "allow `weak` with non-optional type";
+  }
+
+  bool diagnose(const Solution &solution, bool asNote = false) const override;
+
+  static AllowNonOptionalWeak *create(ConstraintSystem &cs,
+                                      ConstraintLocator *locator);
+};
+
 } // end namespace constraints
 } // end namespace swift
 

lib/Sema/CSFix.cpp

@@ -1989,3 +1989,13 @@ AllowInvalidStaticMemberRefOnProtocolMetatype::create(
   return new (cs.getAllocator())
       AllowInvalidStaticMemberRefOnProtocolMetatype(cs, locator);
 }
+
+bool AllowNonOptionalWeak::diagnose(const Solution &solution,
+                                    bool asNote) const {
+  return false;
+}
+
+AllowNonOptionalWeak *AllowNonOptionalWeak::create(ConstraintSystem &cs,
+                                                   ConstraintLocator *locator) {
+  return new (cs.getAllocator()) AllowNonOptionalWeak(cs, locator);
+}

lib/Sema/CSSimplify.cpp

@@ -11544,7 +11544,8 @@ ConstraintSystem::SolutionKind ConstraintSystem::simplifyFixConstraint(
   case FixKind::AllowInvalidStaticMemberRefOnProtocolMetatype:
   case FixKind::AllowWrappedValueMismatch:
   case FixKind::RemoveExtraneousArguments:
-  case FixKind::SpecifyTypeForPlaceholder: {
+  case FixKind::SpecifyTypeForPlaceholder:
+  case FixKind::AllowNonOptionalWeak: {
     return recordFix(fix) ? SolutionKind::Error : SolutionKind::Solved;
   }