[VM] Be more defensive against constants coming from vmservice library (if we skip it)

Change-Id: I23900daadf030dcf46cec11008ec15e43245040f
Reviewed-on: https://dart-review.googlesource.com/52804
Commit-Queue: Martin Kustermann <kustermann@google.com>
Reviewed-by: Vyacheslav Egorov <vegorov@google.com>
Reviewed-by: Alexander Markov <alexmarkov@google.com>

runtime/vm/compiler/frontend/kernel_binary_flowgraph.cc

@@ -10852,8 +10852,13 @@ const Array& ConstantHelper::ReadConstantTable() {
         break;
       }
       case kInstanceConstant: {
-        temp_class_ =
-            H.LookupClassByKernelClass(builder_.ReadCanonicalNameReference());
+        const NameIndex index = builder_.ReadCanonicalNameReference();
+        if (ShouldSkipConstant(index)) {
+          temp_instance_ = Instance::null();
+          break;
+        }
+
+        temp_class_ = H.LookupClassByKernelClass(index);
         temp_object_ = temp_class_.EnsureIsFinalized(H.thread());
         ASSERT(temp_object_.IsNull());
 
@@ -10889,16 +10894,19 @@ const Array& ConstantHelper::ReadConstantTable() {
         const intptr_t entry_index = builder_.ReadUInt();
         temp_object_ = constants.At(entry_index);
 
+        // Happens if the tearoff was in the vmservice library and we have
+        // [skip_vm_service_library] enabled.
+        if (temp_object_.IsNull()) {
+          temp_instance_ = Instance::null();
+          break;
+        }
+
         const intptr_t number_of_type_arguments = builder_.ReadUInt();
-        if (temp_class_.NumTypeArguments() > 0) {
-          temp_type_arguments_ =
-              TypeArguments::New(number_of_type_arguments, Heap::kOld);
-          for (intptr_t j = 0; j < number_of_type_arguments; ++j) {
-            temp_type_arguments_.SetTypeAt(j, type_translator_.BuildType());
-          }
-        } else {
-          ASSERT(number_of_type_arguments == 0);
-          temp_type_arguments_ = TypeArguments::null();
+        ASSERT(number_of_type_arguments > 0);
+        temp_type_arguments_ =
+            TypeArguments::New(number_of_type_arguments, Heap::kOld);
+        for (intptr_t j = 0; j < number_of_type_arguments; ++j) {
+          temp_type_arguments_.SetTypeAt(j, type_translator_.BuildType());
         }
 
         // Make a copy of the old closure, with the delayed type arguments
@@ -10916,12 +10924,7 @@ const Array& ConstantHelper::ReadConstantTable() {
       }
       case kTearOffConstant: {
         const NameIndex index = builder_.ReadCanonicalNameReference();
-        NameIndex lib_index = index;
-        while (!H.IsLibrary(lib_index)) {
-          lib_index = H.CanonicalNameParent(lib_index);
-        }
-        ASSERT(H.IsLibrary(lib_index));
-        if (lib_index == skip_vmservice_library_) {
+        if (ShouldSkipConstant(index)) {
           temp_instance_ = Instance::null();
           break;
         }
@@ -10960,6 +10963,19 @@ void ConstantHelper::InstantiateTypeArguments(const Class& receiver_class,
   *type_arguments = temp_type_.arguments();
 }
 
+// If [index] has `dart:vm_service` as a parent and we are skipping the VM
+// service library, this method returns `true`, otherwise `false`.
+bool ConstantHelper::ShouldSkipConstant(NameIndex index) {
+  if (index == NameIndex::kInvalidName) {
+    return false;
+  }
+  while (!H.IsLibrary(index)) {
+    index = H.CanonicalNameParent(index);
+  }
+  ASSERT(H.IsLibrary(index));
+  return index == skip_vmservice_library_;
+}
+
 }  // namespace kernel
 }  // namespace dart
 

runtime/vm/compiler/frontend/kernel_binary_flowgraph.h

@@ -1704,6 +1704,10 @@ class ConstantHelper {
   void InstantiateTypeArguments(const Class& receiver_class,
                                 TypeArguments* type_arguments);
 
+  // If [index] has `dart:vm_service` as a parent and we are skipping the VM
+  // service library, this method returns `true`, otherwise `false`.
+  bool ShouldSkipConstant(NameIndex index);
+
   NameIndex skip_vmservice_library_;
   ActiveClass* active_class_;
   StreamingFlowGraphBuilder& builder_;

runtime/vm/kernel.h

@@ -16,7 +16,9 @@ namespace dart {
 namespace kernel {
 class NameIndex {
  public:
-  NameIndex() : value_(-1) {}
+  static const int kInvalidName = -1;
+
+  NameIndex() : value_(kInvalidName) {}
   explicit NameIndex(int value) : value_(value) {}
 
   operator int() const { return value_; }