[CSGen] Avoid failing on invalid declarations

include/swift/AST/Types.h

@@ -5736,19 +5736,19 @@ DEFINE_EMPTY_CAN_TYPE_WRAPPER(TypeVariableType, Type)
 /// because the expression is ambiguous. This type is only used by the
 /// constraint solver and transformed into UnresolvedType to be used in AST.
 class HoleType : public TypeBase {
-  using OriginatorType =
-      llvm::PointerUnion<TypeVariableType *, DependentMemberType *>;
+  using Originator = llvm::PointerUnion<TypeVariableType *,
+                                        DependentMemberType *, VarDecl *>;
 
-  OriginatorType Originator;
+  Originator O;
 
-  HoleType(ASTContext &C, OriginatorType originator,
+  HoleType(ASTContext &C, Originator originator,
            RecursiveTypeProperties properties)
-      : TypeBase(TypeKind::Hole, &C, properties), Originator(originator) {}
+      : TypeBase(TypeKind::Hole, &C, properties), O(originator) {}
 
 public:
-  static Type get(ASTContext &ctx, OriginatorType originatorType);
+  static Type get(ASTContext &ctx, Originator originator);
 
-  OriginatorType getOriginatorType() const { return Originator; }
+  Originator getOriginator() const { return O; }
 
   static bool classof(const TypeBase *T) {
     return T->getKind() == TypeKind::Hole;

lib/AST/ASTContext.cpp

@@ -2400,13 +2400,9 @@ Type ErrorType::get(Type originalType) {
   return entry = new (mem) ErrorType(ctx, originalType, properties);
 }
 
-Type HoleType::get(ASTContext &ctx, OriginatorType originator) {
+Type HoleType::get(ASTContext &ctx, Originator originator) {
   assert(originator);
-  auto properties = reinterpret_cast<TypeBase *>(originator.getOpaqueValue())
-                        ->getRecursiveProperties();
-  properties |= RecursiveTypeProperties::HasTypeHole;
-
-  auto arena = getArena(properties);
+  auto arena = getArena(RecursiveTypeProperties::HasTypeHole);
   return new (ctx, arena)
       HoleType(ctx, originator, RecursiveTypeProperties::HasTypeHole);
 }

lib/AST/ASTDumper.cpp

@@ -3512,12 +3512,14 @@ namespace {
 
     void visitHoleType(HoleType *T, StringRef label) {
       printCommon(label, "hole_type");
-      auto originatorTy = T->getOriginatorType();
-      if (auto *typeVar = originatorTy.dyn_cast<TypeVariableType *>()) {
+      auto originator = T->getOriginator();
+      if (auto *typeVar = originator.dyn_cast<TypeVariableType *>()) {
         printRec("type_variable", typeVar);
+      } else if (auto *VD = originator.dyn_cast<VarDecl *>()) {
+        VD->dumpRef(PrintWithColorRAII(OS, DeclColor).getOS());
       } else {
         printRec("dependent_member_type",
-                 originatorTy.get<DependentMemberType *>());
+                 originator.get<DependentMemberType *>());
       }
       PrintWithColorRAII(OS, ParenthesisColor) << ')';
     }

lib/AST/ASTPrinter.cpp

@@ -3822,8 +3822,15 @@ class TypePrinter : public TypeVisitor<TypePrinter> {
   void visitHoleType(HoleType *T) {
     if (Options.PrintTypesForDebugging) {
       Printer << "<<hole for ";
-      auto originatorTy = T->getOriginatorType();
-      visit(Type(reinterpret_cast<TypeBase *>(originatorTy.getOpaqueValue())));
+      auto originator = T->getOriginator();
+      if (auto *typeVar = originator.dyn_cast<TypeVariableType *>()) {
+        visit(typeVar);
+      } else if (auto *VD = originator.dyn_cast<VarDecl *>()) {
+        Printer << "decl = ";
+        Printer << VD->getName();
+      } else {
+        visit(originator.get<DependentMemberType *>());
+      }
       Printer << ">>";
     } else {
       Printer << "<<hole>>";

lib/Sema/CSGen.cpp

@@ -1241,19 +1241,20 @@ namespace {
       if (auto *VD = dyn_cast<VarDecl>(E->getDecl())) {
         knownType = CS.getTypeIfAvailable(VD);
         if (!knownType)
-          knownType = VD->getType();
+          knownType = CS.getVarType(VD);
 
         if (knownType) {
-          assert(!knownType->isHole());
           // If the known type has an error, bail out.
           if (knownType->hasError()) {
             if (!CS.hasType(E))
               CS.setType(E, knownType);
             return nullptr;
           }
 
-          // Set the favored type for this expression to the known type.
-          CS.setFavoredType(E, knownType.getPointer());
+          if (!knownType->hasHole()) {
+            // Set the favored type for this expression to the known type.
+            CS.setFavoredType(E, knownType.getPointer());
+          }
         }
 
         // This can only happen when failure diagnostics is trying
@@ -2016,7 +2017,7 @@ namespace {
 
           Type externalType;
           if (param->getTypeRepr()) {
-            auto declaredTy = param->getType();
+            auto declaredTy = CS.getVarType(param);
             externalType = CS.openUnboundGenericTypes(declaredTy, paramLoc);
           } else {
             // Let's allow parameters which haven't been explicitly typed
@@ -3884,7 +3885,7 @@ bool ConstraintSystem::generateConstraints(
                                                getConstraintLocator(typeRepr));
     setType(typeRepr, backingType);
 
-    auto propertyType = wrappedVar->getType();
+    auto propertyType = getVarType(wrappedVar);
     if (propertyType->hasError())
       return true;
 

lib/Sema/CSSimplify.cpp

@@ -7016,7 +7016,7 @@ ConstraintSystem::SolutionKind ConstraintSystem::simplifyMemberConstraint(
       // type but a hole.
       auto shouldRecordFixForHole = [&](HoleType *baseType) {
         auto *originator =
-            baseType->getOriginatorType().dyn_cast<TypeVariableType *>();
+            baseType->getOriginator().dyn_cast<TypeVariableType *>();
 
         if (!originator)
           return false;

lib/Sema/ConstraintSystem.cpp

@@ -5213,3 +5213,21 @@ void ConstraintSystem::recordFixedRequirement(ConstraintLocator *reqLocator,
         std::make_tuple(GP, reqKind, requirementTy.getPointer()));
   }
 }
+
+// Replace any error types encountered with holes.
+Type ConstraintSystem::getVarType(const VarDecl *var) {
+  auto type = var->getType();
+
+  // If this declaration is used as part of a code completion
+  // expression, solver needs to glance over the fact that
+  // it might be invalid to avoid failing constraint generation
+  // and produce completion results.
+  if (!isForCodeCompletion())
+    return type;
+
+  return type.transform([&](Type type) {
+    if (!type->is<ErrorType>())
+      return type;
+    return HoleType::get(Context, const_cast<VarDecl *>(var));
+  });
+}

lib/Sema/ConstraintSystem.h

@@ -1293,6 +1293,11 @@ enum class ConstraintSystemFlags {
   /// Don't try to type check closure bodies, and leave them unchecked. This is
   /// used for source tooling functionalities.
   LeaveClosureBodyUnchecked = 0x20,
+
+  /// If set, we are solving specifically to determine the type of a
+  /// CodeCompletionExpr, and should continue in the presence of errors wherever
+  /// possible.
+  ForCodeCompletion = 0x40,
 };
 
 /// Options that affect the constraint system as a whole.
@@ -2834,6 +2839,11 @@ class ConstraintSystem {
     return known->second;
   }
 
+  /// Retrieve type type of the given declaration to be used in
+  /// constraint system, this is better than calling `getType()`
+  /// directly because it accounts of constraint system flags.
+  Type getVarType(const VarDecl *var);
+
   /// Cache the type of the expression argument and return that same
   /// argument.
   template <typename T>
@@ -3057,6 +3067,12 @@ class ConstraintSystem {
     return Options.contains(ConstraintSystemFlags::ReusePrecheckedType);
   }
 
+  /// Whether we are solving to determine the possible types of a
+  /// \c CodeCompletionExpr.
+  bool isForCodeCompletion() const {
+    return Options.contains(ConstraintSystemFlags::ForCodeCompletion);
+  }
+
   /// Log and record the application of the fix. Return true iff any
   /// subsequent solution would be worse than the best known solution.
   bool recordFix(ConstraintFix *fix, unsigned impact = 1);

lib/Sema/TypeCheckCodeCompletion.cpp

@@ -1012,7 +1012,7 @@ sawSolution(const constraints::Solution &S) {
       return S.simplifyType(completionTy.transform([&](Type type) {
         if (auto *hole = type->getAs<HoleType>()) {
           if (auto *typeVar =
-                  hole->getOriginatorType().dyn_cast<TypeVariableType *>()) {
+                  hole->getOriginator().dyn_cast<TypeVariableType *>()) {
             if (auto *GP = typeVar->getImpl().getGenericParameter()) {
               // Code completion depends on generic parameter type being
               // represented in terms of `ArchetypeType` since it's easy