[CSFix] Introduce a fix for inaccessible members

If there are no other choices, let's attempt to
use any available inaccessible candidates.

Author: xedin

lib/Sema/CSFix.cpp

@@ -384,3 +384,13 @@ MoveOutOfOrderArgument *MoveOutOfOrderArgument::create(
   return new (cs.getAllocator())
       MoveOutOfOrderArgument(cs, argIdx, prevArgIdx, bindings, locator);
 }
+
+bool AllowInaccessibleMember::diagnose(Expr *root, bool asNote) const {
+  return false;
+}
+
+AllowInaccessibleMember *
+AllowInaccessibleMember::create(ConstraintSystem &cs, ValueDecl *member,
+                                ConstraintLocator *locator) {
+  return new (cs.getAllocator()) AllowInaccessibleMember(cs, member, locator);
+}

lib/Sema/CSFix.h

@@ -132,6 +132,10 @@ enum class FixKind : uint8_t {
 
   /// If there is out-of-order argument, let's fix that by re-ordering.
   MoveOutOfOrderArgument,
+
+  /// If there is a matching inaccessible member - allow it as if there
+  /// no access control.
+  AllowInaccessibleMember,
 };
 
 class ConstraintFix {
@@ -713,6 +717,26 @@ class MoveOutOfOrderArgument final : public ConstraintFix {
                                         ConstraintLocator *locator);
 };
 
+class AllowInaccessibleMember final : public ConstraintFix {
+  ValueDecl *Member;
+
+  AllowInaccessibleMember(ConstraintSystem &cs, ValueDecl *member,
+                          ConstraintLocator *locator)
+      : ConstraintFix(cs, FixKind::AllowInaccessibleMember, locator),
+        Member(member) {}
+
+public:
+  std::string getName() const override {
+    return "allow inaccessible member reference";
+  }
+
+  bool diagnose(Expr *root, bool asNote = false) const override;
+
+  static AllowInaccessibleMember *create(ConstraintSystem &cs,
+                                         ValueDecl *member,
+                                         ConstraintLocator *locator);
+};
+
 } // end namespace constraints
 } // end namespace swift
 

lib/Sema/CSSimplify.cpp

@@ -4160,10 +4160,12 @@ fixMemberRef(ConstraintSystem &cs, Type baseTy,
     case MemberLookupResult::UR_TypeMemberOnInstance:
       return AllowTypeOrInstanceMember::create(cs, baseTy, memberName, locator);
 
+    case MemberLookupResult::UR_Inaccessible:
+      return AllowInaccessibleMember::create(cs, decl, locator);
+
     case MemberLookupResult::UR_MutatingMemberOnRValue:
     case MemberLookupResult::UR_MutatingGetterOnRValue:
     case MemberLookupResult::UR_LabelMismatch:
-    case MemberLookupResult::UR_Inaccessible:
     case MemberLookupResult::UR_UnavailableInExistential:
       break;
     }
@@ -4187,9 +4189,9 @@ ConstraintSystem::SolutionKind ConstraintSystem::simplifyMemberConstraint(
 
   auto locator = getConstraintLocator(locatorB);
   MemberLookupResult result =
-    performMemberLookup(kind, member, baseTy, functionRefKind, locator,
-                        /*includeInaccessibleMembers*/false);
-  
+      performMemberLookup(kind, member, baseTy, functionRefKind, locator,
+                          /*includeInaccessibleMembers*/ shouldAttemptFixes());
+
   switch (result.OverallResult) {
   case MemberLookupResult::Unsolved:
     // If requested, generate a constraint.
@@ -6195,6 +6197,7 @@ ConstraintSystem::SolutionKind ConstraintSystem::simplifyFixConstraint(
   case FixKind::AllowInvalidInitRef:
   case FixKind::AllowClosureParameterDestructuring:
   case FixKind::MoveOutOfOrderArgument:
+  case FixKind::AllowInaccessibleMember:
     llvm_unreachable("handled elsewhere");
   }