[CSFix] InitAccessors: Add a fix that tracks invalid member references within init accessors

Author: xedin

include/swift/Sema/CSFix.h

@@ -447,6 +447,10 @@ enum class FixKind : uint8_t {
 
   /// Ignore missing 'each' keyword before value pack reference.
   IgnoreMissingEachKeyword,
+
+  /// Ignore the fact that member couldn't be referenced within init accessor
+  /// because its name doesn't appear in 'initializes' or 'accesses' attributes.
+  AllowInvalidMemberReferenceInInitAccessor,
 };
 
 class ConstraintFix {
@@ -3536,6 +3540,39 @@ class IgnoreMissingEachKeyword final : public ConstraintFix {
   }
 };
 
+class AllowInvalidMemberReferenceInInitAccessor final : public ConstraintFix {
+  DeclNameRef MemberName;
+
+  AllowInvalidMemberReferenceInInitAccessor(ConstraintSystem &cs,
+                                            DeclNameRef memberName,
+                                            ConstraintLocator *locator)
+      : ConstraintFix(cs, FixKind::AllowInvalidMemberReferenceInInitAccessor,
+                      locator),
+        MemberName(memberName) {}
+
+public:
+  std::string getName() const override {
+    llvm::SmallVector<char, 16> scratch;
+    auto memberName = MemberName.getString(scratch);
+    return "allow reference to member '" + memberName.str() +
+           "' in init accessor";
+  }
+
+  bool diagnose(const Solution &solution, bool asNote = false) const override;
+
+  bool diagnoseForAmbiguity(CommonFixesArray commonFixes) const override {
+    return diagnose(*commonFixes.front().first);
+  }
+
+  static AllowInvalidMemberReferenceInInitAccessor *
+  create(ConstraintSystem &cs, DeclNameRef memberName,
+         ConstraintLocator *locator);
+
+  static bool classof(const ConstraintFix *fix) {
+    return fix->getKind() == FixKind::AllowInvalidMemberReferenceInInitAccessor;
+  }
+};
+
 } // end namespace constraints
 } // end namespace swift
 

lib/Sema/CSFix.cpp

@@ -2796,3 +2796,16 @@ IgnoreMissingEachKeyword::create(ConstraintSystem &cs, Type valuePackTy,
   return new (cs.getAllocator())
       IgnoreMissingEachKeyword(cs, valuePackTy, locator);
 }
+
+bool AllowInvalidMemberReferenceInInitAccessor::diagnose(
+    const Solution &solution, bool asNote) const {
+  return false;
+}
+
+AllowInvalidMemberReferenceInInitAccessor *
+AllowInvalidMemberReferenceInInitAccessor::create(ConstraintSystem &cs,
+                                                  DeclNameRef memberName,
+                                                  ConstraintLocator *locator) {
+  return new (cs.getAllocator())
+      AllowInvalidMemberReferenceInInitAccessor(cs, memberName, locator);
+}

lib/Sema/CSSimplify.cpp

@@ -10248,7 +10248,8 @@ fixMemberRef(ConstraintSystem &cs, Type baseTy,
       return AllowInvalidStaticMemberRefOnProtocolMetatype::create(cs, locator);
 
     case MemberLookupResult::UR_UnavailableWithinInitAccessor:
-      return nullptr;
+      return AllowInvalidMemberReferenceInInitAccessor::create(cs, memberName,
+                                                               locator);
     }
   }
 
@@ -14674,6 +14675,10 @@ ConstraintSystem::SolutionKind ConstraintSystem::simplifyFixConstraint(
     return recordFix(fix, 100) ? SolutionKind::Error : SolutionKind::Solved;
   }
 
+  case FixKind::AllowInvalidMemberReferenceInInitAccessor: {
+    return recordFix(fix, 5) ? SolutionKind::Error : SolutionKind::Solved;
+  }
+
   case FixKind::ExplicitlyConstructRawRepresentable: {
     // Let's increase impact of this fix for binary operators because
     // it's possible to get both `.rawValue` and construction fixes for