Revert "[vm] Check prefix.loadLibrary is called and returns before prefix members are used."

This reverts commit f049a410e5.

Reason for revert: Broke reload bots.

Original change's description:
> [vm] Check prefix.loadLibrary is called and returns before prefix members are used.
> 
> Not loading is actually deferred.
> 
> Bug: https://github.com/dart-lang/sdk/issues/41974
> Change-Id: I62688007bd36dbcb2e8ffb4a1fd2dceb1775b1c8
> Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/149053
> Commit-Queue: Ryan Macnak <rmacnak@google.com>
> Reviewed-by: Siva Annamalai <asiva@google.com>

TBR=rmacnak@google.com,alexmarkov@google.com,asiva@google.com

Change-Id: I923e339465fdf13199efc11a9cef4a842abebd67
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: https://github.com/dart-lang/sdk/issues/41974
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/149423
Reviewed-by: Aske Simon Christensen <askesc@google.com>
Commit-Queue: Aske Simon Christensen <askesc@google.com>

runtime/lib/object.cc

@@ -196,19 +196,6 @@ DEFINE_NATIVE_ENTRY(Type_equality, 0, 2) {
   return Bool::Get(type.IsEquivalent(other, TypeEquality::kSyntactical)).raw();
 }
 
-DEFINE_NATIVE_ENTRY(LibraryPrefix_isLoaded, 0, 1) {
-  const LibraryPrefix& prefix =
-      LibraryPrefix::CheckedHandle(zone, arguments->NativeArgAt(0));
-  return Bool::Get(prefix.is_loaded()).raw();
-}
-
-DEFINE_NATIVE_ENTRY(LibraryPrefix_setLoaded, 0, 1) {
-  const LibraryPrefix& prefix =
-      LibraryPrefix::CheckedHandle(zone, arguments->NativeArgAt(0));
-  prefix.set_is_loaded(true);
-  return Instance::null();
-}
-
 DEFINE_NATIVE_ENTRY(Internal_inquireIs64Bit, 0, 0) {
 #if defined(ARCH_IS_64_BIT)
   return Bool::True().raw();

runtime/vm/bootstrap_natives.h

@@ -31,8 +31,6 @@ namespace dart {
   V(AbstractType_toString, 1)                                                  \
   V(Type_getHashCode, 1)                                                       \
   V(Type_equality, 2)                                                          \
-  V(LibraryPrefix_isLoaded, 1)                                                 \
-  V(LibraryPrefix_setLoaded, 1)                                                \
   V(Identical_comparison, 2)                                                   \
   V(Integer_bitAndFromInteger, 2)                                              \
   V(Integer_bitOrFromInteger, 2)                                               \

runtime/vm/clustered_snapshot.cc

@@ -3248,7 +3248,6 @@ class LibraryPrefixDeserializationCluster : public DeserializationCluster {
       ReadFromTo(prefix);
       prefix->ptr()->num_imports_ = d->Read<uint16_t>();
       prefix->ptr()->is_deferred_load_ = d->Read<bool>();
-      prefix->ptr()->is_loaded_ = false;
     }
   }
 };

runtime/vm/compiler/backend/il.cc

@@ -1099,8 +1099,7 @@ ConstantInstr::ConstantInstr(const Object& value, TokenPosition token_pos)
     // tables used for certain character classes are represented as TypedData,
     // and so those values are also neither immutable (as there are no immutable
     // TypedData values) or canonical.
-    ASSERT(value.IsTypeParameter() || value.IsArray() || value.IsTypedData() ||
-           value.IsLibraryPrefix());
+    ASSERT(value.IsTypeParameter() || value.IsArray() || value.IsTypedData());
   }
 #endif
 }

runtime/vm/compiler/frontend/kernel_binary_flowgraph.cc

@@ -1363,9 +1363,9 @@ Fragment StreamingFlowGraphBuilder::BuildExpression(TokenPosition* position) {
     case kInstantiation:
       return BuildPartialTearoffInstantiation(position);
     case kLoadLibrary:
-      return BuildLibraryPrefixAction(position, Symbols::LoadLibrary());
     case kCheckLibraryIsLoaded:
-      return BuildLibraryPrefixAction(position, Symbols::CheckLoaded());
+      ReadUInt();  // skip library index
+      return BuildFutureNullValue(position);
     case kConstStaticInvocation:
     case kConstConstructorInvocation:
     case kConstListLiteral:
@@ -4067,26 +4067,6 @@ Fragment StreamingFlowGraphBuilder::BuildPartialTearoffInstantiation(
   return instructions;
 }
 
-Fragment StreamingFlowGraphBuilder::BuildLibraryPrefixAction(
-    TokenPosition* position,
-    const String& selector) {
-  const intptr_t dependency_index = ReadUInt();
-  const Library& current_library = Library::Handle(
-      Z, Class::Handle(Z, parsed_function()->function().Owner()).library());
-  const Array& dependencies = Array::Handle(Z, current_library.dependencies());
-  const LibraryPrefix& prefix =
-      LibraryPrefix::CheckedZoneHandle(Z, dependencies.At(dependency_index));
-  const Function& function =
-      Function::ZoneHandle(Z, Library::Handle(Z, Library::CoreLibrary())
-                                  .LookupFunctionAllowPrivate(selector));
-  ASSERT(!function.IsNull());
-  Fragment instructions;
-  instructions += Constant(prefix);
-  instructions +=
-      StaticCall(TokenPosition::kNoSource, function, 1, ICData::kStatic);
-  return instructions;
-}
-
 Fragment StreamingFlowGraphBuilder::BuildExpressionStatement() {
   Fragment instructions = BuildExpression();  // read expression.
   instructions += Drop();

runtime/vm/compiler/frontend/kernel_binary_flowgraph.h

@@ -335,8 +335,6 @@ class StreamingFlowGraphBuilder : public KernelReaderHelper {
   Fragment BuildFutureNullValue(TokenPosition* position);
   Fragment BuildConstantExpression(TokenPosition* position, Tag tag);
   Fragment BuildPartialTearoffInstantiation(TokenPosition* position);
-  Fragment BuildLibraryPrefixAction(TokenPosition* position,
-                                    const String& selector);
 
   Fragment BuildExpressionStatement();
   Fragment BuildBlock();

runtime/vm/compiler/runtime_offsets_extracted.h

@@ -442,7 +442,7 @@ static constexpr dart::compiler::target::word Integer_InstanceSize = 4;
 static constexpr dart::compiler::target::word KernelProgramInfo_InstanceSize =
     64;
 static constexpr dart::compiler::target::word LanguageError_InstanceSize = 28;
-static constexpr dart::compiler::target::word Library_InstanceSize = 80;
+static constexpr dart::compiler::target::word Library_InstanceSize = 76;
 static constexpr dart::compiler::target::word LibraryPrefix_InstanceSize = 20;
 static constexpr dart::compiler::target::word LinkedHashMap_InstanceSize = 28;
 static constexpr dart::compiler::target::word LocalVarDescriptors_InstanceSize =
@@ -927,7 +927,7 @@ static constexpr dart::compiler::target::word Integer_InstanceSize = 8;
 static constexpr dart::compiler::target::word KernelProgramInfo_InstanceSize =
     128;
 static constexpr dart::compiler::target::word LanguageError_InstanceSize = 48;
-static constexpr dart::compiler::target::word Library_InstanceSize = 152;
+static constexpr dart::compiler::target::word Library_InstanceSize = 144;
 static constexpr dart::compiler::target::word LibraryPrefix_InstanceSize = 40;
 static constexpr dart::compiler::target::word LinkedHashMap_InstanceSize = 56;
 static constexpr dart::compiler::target::word LocalVarDescriptors_InstanceSize =
@@ -1404,7 +1404,7 @@ static constexpr dart::compiler::target::word Integer_InstanceSize = 4;
 static constexpr dart::compiler::target::word KernelProgramInfo_InstanceSize =
     64;
 static constexpr dart::compiler::target::word LanguageError_InstanceSize = 28;
-static constexpr dart::compiler::target::word Library_InstanceSize = 80;
+static constexpr dart::compiler::target::word Library_InstanceSize = 76;
 static constexpr dart::compiler::target::word LibraryPrefix_InstanceSize = 20;
 static constexpr dart::compiler::target::word LinkedHashMap_InstanceSize = 28;
 static constexpr dart::compiler::target::word LocalVarDescriptors_InstanceSize =
@@ -1890,7 +1890,7 @@ static constexpr dart::compiler::target::word Integer_InstanceSize = 8;
 static constexpr dart::compiler::target::word KernelProgramInfo_InstanceSize =
     128;
 static constexpr dart::compiler::target::word LanguageError_InstanceSize = 48;
-static constexpr dart::compiler::target::word Library_InstanceSize = 152;
+static constexpr dart::compiler::target::word Library_InstanceSize = 144;
 static constexpr dart::compiler::target::word LibraryPrefix_InstanceSize = 40;
 static constexpr dart::compiler::target::word LinkedHashMap_InstanceSize = 56;
 static constexpr dart::compiler::target::word LocalVarDescriptors_InstanceSize =
@@ -2366,7 +2366,7 @@ static constexpr dart::compiler::target::word Integer_InstanceSize = 4;
 static constexpr dart::compiler::target::word KernelProgramInfo_InstanceSize =
     64;
 static constexpr dart::compiler::target::word LanguageError_InstanceSize = 28;
-static constexpr dart::compiler::target::word Library_InstanceSize = 80;
+static constexpr dart::compiler::target::word Library_InstanceSize = 76;
 static constexpr dart::compiler::target::word LibraryPrefix_InstanceSize = 20;
 static constexpr dart::compiler::target::word LinkedHashMap_InstanceSize = 28;
 static constexpr dart::compiler::target::word LocalVarDescriptors_InstanceSize =
@@ -2845,7 +2845,7 @@ static constexpr dart::compiler::target::word Integer_InstanceSize = 8;
 static constexpr dart::compiler::target::word KernelProgramInfo_InstanceSize =
     128;
 static constexpr dart::compiler::target::word LanguageError_InstanceSize = 48;
-static constexpr dart::compiler::target::word Library_InstanceSize = 152;
+static constexpr dart::compiler::target::word Library_InstanceSize = 144;
 static constexpr dart::compiler::target::word LibraryPrefix_InstanceSize = 40;
 static constexpr dart::compiler::target::word LinkedHashMap_InstanceSize = 56;
 static constexpr dart::compiler::target::word LocalVarDescriptors_InstanceSize =
@@ -3316,7 +3316,7 @@ static constexpr dart::compiler::target::word Integer_InstanceSize = 4;
 static constexpr dart::compiler::target::word KernelProgramInfo_InstanceSize =
     64;
 static constexpr dart::compiler::target::word LanguageError_InstanceSize = 28;
-static constexpr dart::compiler::target::word Library_InstanceSize = 80;
+static constexpr dart::compiler::target::word Library_InstanceSize = 76;
 static constexpr dart::compiler::target::word LibraryPrefix_InstanceSize = 20;
 static constexpr dart::compiler::target::word LinkedHashMap_InstanceSize = 28;
 static constexpr dart::compiler::target::word LocalVarDescriptors_InstanceSize =
@@ -3796,7 +3796,7 @@ static constexpr dart::compiler::target::word Integer_InstanceSize = 8;
 static constexpr dart::compiler::target::word KernelProgramInfo_InstanceSize =
     128;
 static constexpr dart::compiler::target::word LanguageError_InstanceSize = 48;
-static constexpr dart::compiler::target::word Library_InstanceSize = 152;
+static constexpr dart::compiler::target::word Library_InstanceSize = 144;
 static constexpr dart::compiler::target::word LibraryPrefix_InstanceSize = 40;
 static constexpr dart::compiler::target::word LinkedHashMap_InstanceSize = 56;
 static constexpr dart::compiler::target::word LocalVarDescriptors_InstanceSize =
@@ -4307,7 +4307,7 @@ static constexpr dart::compiler::target::word
     AOT_KernelProgramInfo_InstanceSize = 64;
 static constexpr dart::compiler::target::word AOT_LanguageError_InstanceSize =
     28;
-static constexpr dart::compiler::target::word AOT_Library_InstanceSize = 76;
+static constexpr dart::compiler::target::word AOT_Library_InstanceSize = 72;
 static constexpr dart::compiler::target::word AOT_LibraryPrefix_InstanceSize =
     20;
 static constexpr dart::compiler::target::word AOT_LinkedHashMap_InstanceSize =
@@ -4833,7 +4833,7 @@ static constexpr dart::compiler::target::word
     AOT_KernelProgramInfo_InstanceSize = 128;
 static constexpr dart::compiler::target::word AOT_LanguageError_InstanceSize =
     48;
-static constexpr dart::compiler::target::word AOT_Library_InstanceSize = 144;
+static constexpr dart::compiler::target::word AOT_Library_InstanceSize = 136;
 static constexpr dart::compiler::target::word AOT_LibraryPrefix_InstanceSize =
     40;
 static constexpr dart::compiler::target::word AOT_LinkedHashMap_InstanceSize =
@@ -5363,7 +5363,7 @@ static constexpr dart::compiler::target::word
     AOT_KernelProgramInfo_InstanceSize = 128;
 static constexpr dart::compiler::target::word AOT_LanguageError_InstanceSize =
     48;
-static constexpr dart::compiler::target::word AOT_Library_InstanceSize = 144;
+static constexpr dart::compiler::target::word AOT_Library_InstanceSize = 136;
 static constexpr dart::compiler::target::word AOT_LibraryPrefix_InstanceSize =
     40;
 static constexpr dart::compiler::target::word AOT_LinkedHashMap_InstanceSize =
@@ -5880,7 +5880,7 @@ static constexpr dart::compiler::target::word
     AOT_KernelProgramInfo_InstanceSize = 64;
 static constexpr dart::compiler::target::word AOT_LanguageError_InstanceSize =
     28;
-static constexpr dart::compiler::target::word AOT_Library_InstanceSize = 76;
+static constexpr dart::compiler::target::word AOT_Library_InstanceSize = 72;
 static constexpr dart::compiler::target::word AOT_LibraryPrefix_InstanceSize =
     20;
 static constexpr dart::compiler::target::word AOT_LinkedHashMap_InstanceSize =
@@ -6399,7 +6399,7 @@ static constexpr dart::compiler::target::word
     AOT_KernelProgramInfo_InstanceSize = 128;
 static constexpr dart::compiler::target::word AOT_LanguageError_InstanceSize =
     48;
-static constexpr dart::compiler::target::word AOT_Library_InstanceSize = 144;
+static constexpr dart::compiler::target::word AOT_Library_InstanceSize = 136;
 static constexpr dart::compiler::target::word AOT_LibraryPrefix_InstanceSize =
     40;
 static constexpr dart::compiler::target::word AOT_LinkedHashMap_InstanceSize =
@@ -6922,7 +6922,7 @@ static constexpr dart::compiler::target::word
     AOT_KernelProgramInfo_InstanceSize = 128;
 static constexpr dart::compiler::target::word AOT_LanguageError_InstanceSize =
     48;
-static constexpr dart::compiler::target::word AOT_Library_InstanceSize = 144;
+static constexpr dart::compiler::target::word AOT_Library_InstanceSize = 136;
 static constexpr dart::compiler::target::word AOT_LibraryPrefix_InstanceSize =
     40;
 static constexpr dart::compiler::target::word AOT_LinkedHashMap_InstanceSize =

runtime/vm/kernel_loader.cc

@@ -1305,7 +1305,6 @@ void KernelLoader::LoadLibraryImportsAndExports(Library* library,
   LibraryPrefix& library_prefix = LibraryPrefix::Handle(Z);
 
   const intptr_t deps_count = helper_.ReadListLength();
-  const Array& deps = Array::Handle(Array::New(deps_count));
   for (intptr_t dep = 0; dep < deps_count; ++dep) {
     LibraryDependencyHelper dependency_helper(&helper_);
 
@@ -1389,21 +1388,12 @@ void KernelLoader::LoadLibraryImportsAndExports(Library* library,
         }
       }
     }
-
     if (FLAG_enable_mirrors && dependency_helper.annotation_count_ > 0) {
       ASSERT(annotations_kernel_offset > 0);
       ns.AddMetadata(toplevel_class, TokenPosition::kNoSource,
                      annotations_kernel_offset);
     }
-
-    if (prefix.IsNull()) {
-      deps.SetAt(dep, ns);
-    } else {
-      deps.SetAt(dep, library_prefix);
-    }
   }
-
-  library->set_dependencies(deps);
 }
 
 void KernelLoader::LoadPreliminaryClass(ClassHelper* class_helper,

runtime/vm/object.cc

@@ -11047,6 +11047,27 @@ void ClassDictionaryIterator::MoveToNextClass() {
   }
 }
 
+LibraryPrefixIterator::LibraryPrefixIterator(const Library& library)
+    : DictionaryIterator(library) {
+  Advance();
+}
+
+LibraryPrefixPtr LibraryPrefixIterator::GetNext() {
+  ASSERT(HasNext());
+  int ix = next_ix_++;
+  Object& obj = Object::Handle(array_.At(ix));
+  Advance();
+  return LibraryPrefix::Cast(obj).raw();
+}
+
+void LibraryPrefixIterator::Advance() {
+  Object& obj = Object::Handle(array_.At(next_ix_));
+  while (!obj.IsLibraryPrefix() && HasNext()) {
+    next_ix_++;
+    obj = array_.At(next_ix_);
+  }
+}
+
 static void ReportTooManyImports(const Library& lib) {
   const String& url = String::Handle(lib.url());
   Report::MessageF(Report::kError, Script::Handle(lib.LookupScript(url)),
@@ -12020,10 +12041,6 @@ void Library::set_toplevel_class(const Class& value) const {
   StorePointer(&raw_ptr()->toplevel_class_, value.raw());
 }
 
-void Library::set_dependencies(const Array& deps) const {
-  StorePointer(&raw_ptr()->dependencies_, deps.raw());
-}
-
 void Library::set_metadata(const GrowableObjectArray& value) const {
   StorePointer(&raw_ptr()->metadata_, value.raw());
 }
@@ -12892,7 +12909,6 @@ LibraryPrefixPtr LibraryPrefix::New(const String& name,
   result.set_num_imports(0);
   result.set_importer(importer);
   result.StoreNonPointer(&result.raw_ptr()->is_deferred_load_, deferred_load);
-  result.StoreNonPointer(&result.raw_ptr()->is_loaded_, false);
   result.set_imports(Array::Handle(Array::New(kInitialSize)));
   result.AddImport(import);
   return result.raw();
@@ -12920,7 +12936,8 @@ void LibraryPrefix::set_importer(const Library& value) const {
 
 const char* LibraryPrefix::ToCString() const {
   const String& prefix = String::Handle(name());
-  return prefix.ToCString();
+  return OS::SCreate(Thread::Current()->zone(), "LibraryPrefix:'%s'",
+                     prefix.ToCString());
 }
 
 void Namespace::set_metadata_field(const Field& value) const {

runtime/vm/object.h

@@ -4519,6 +4519,7 @@ class DictionaryIterator : public ValueObject {
   int next_ix_;     // Index of next element.
 
   friend class ClassDictionaryIterator;
+  friend class LibraryPrefixIterator;
   DISALLOW_COPY_AND_ASSIGN(DictionaryIterator);
 };
 
@@ -4549,6 +4550,16 @@ class ClassDictionaryIterator : public DictionaryIterator {
   DISALLOW_COPY_AND_ASSIGN(ClassDictionaryIterator);
 };
 
+class LibraryPrefixIterator : public DictionaryIterator {
+ public:
+  explicit LibraryPrefixIterator(const Library& library);
+  LibraryPrefixPtr GetNext();
+
+ private:
+  void Advance();
+  DISALLOW_COPY_AND_ASSIGN(LibraryPrefixIterator);
+};
+
 class Library : public Object {
  public:
   StringPtr name() const { return raw_ptr()->name_; }
@@ -4703,9 +4714,6 @@ class Library : public Object {
   NamespacePtr ImportAt(intptr_t index) const;
   LibraryPtr ImportLibraryAt(intptr_t index) const;
 
-  ArrayPtr dependencies() const { return raw_ptr()->dependencies_; }
-  void set_dependencies(const Array& deps) const;
-
   void DropDependenciesAndCaches() const;
 
   // Resolving native methods for script loaded in the library.
@@ -7311,10 +7319,6 @@ class LibraryPrefix : public Instance {
   void AddImport(const Namespace& import) const;
 
   bool is_deferred_load() const { return raw_ptr()->is_deferred_load_; }
-  bool is_loaded() const { return raw_ptr()->is_loaded_; }
-  void set_is_loaded(bool value) const {
-    return StoreNonPointer(&raw_ptr()->is_loaded_, value);
-  }
 
   static intptr_t InstanceSize() {
     return RoundedAllocationSize(sizeof(LibraryPrefixLayout));

runtime/vm/raw_object.h

@@ -1305,12 +1305,11 @@ class LibraryLayout : public ObjectLayout {
   GrowableObjectArrayPtr used_scripts_;
   ArrayPtr imports_;  // List of Namespaces imported without prefix.
   ArrayPtr exports_;  // List of re-exported Namespaces.
-  ArrayPtr dependencies_;
   ExternalTypedDataPtr kernel_data_;
   ObjectPtr* to_snapshot(Snapshot::Kind kind) {
     switch (kind) {
       case Snapshot::kFullAOT:
-        return reinterpret_cast<ObjectPtr*>(&dependencies_);
+        return reinterpret_cast<ObjectPtr*>(&exports_);
       case Snapshot::kFull:
       case Snapshot::kFullJIT:
         return reinterpret_cast<ObjectPtr*>(&kernel_data_);
@@ -2131,7 +2130,6 @@ class LibraryPrefixLayout : public InstanceLayout {
   }
   uint16_t num_imports_;  // Number of library entries in libraries_.
   bool is_deferred_load_;
-  bool is_loaded_;
 };
 
 class TypeArgumentsLayout : public InstanceLayout {

runtime/vm/symbols.h

@@ -44,7 +44,6 @@ class ObjectPointerVisitor;
   V(Call, "call")                                                              \
   V(Cancel, "cancel")                                                          \
   V(CastError, "_CastError")                                                   \
-  V(CheckLoaded, "_checkLoaded")                                               \
   V(Class, "Class")                                                            \
   V(ClassID, "ClassID")                                                        \
   V(ClearAsyncThreadStackTrace, "_clearAsyncThreadStackTrace")                 \
@@ -206,7 +205,6 @@ class ObjectPointerVisitor;
   V(ListFactory, "List.")                                                      \
   V(ListFilledFactory, "List.filled")                                          \
   V(ListLiteralFactory, "List._fromLiteral")                                   \
-  V(LoadLibrary, "_loadLibrary")                                               \
   V(LocalVarDescriptors, "LocalVarDescriptors")                                \
   V(Map, "Map")                                                                \
   V(MapLiteralFactory, "Map._fromLiteral")                                     \

sdk/lib/_internal/vm/lib/lib_prefix.dart

@@ -13,32 +13,7 @@ class _LibraryPrefix {
     throw "Unreachable";
   }
 
-  bool _isLoaded() native "LibraryPrefix_isLoaded";
-  void _setLoaded() native "LibraryPrefix_setLoaded";
-}
-
-class _DeferredNotLoadedError extends Error implements NoSuchMethodError {
-  _LibraryPrefix prefix;
-
-  _DeferredNotLoadedError(this.prefix);
-
-  String toString() {
-    return "Deferred library $prefix was not loaded.";
-  }
-}
-
-@pragma("vm:entry-point")
-@pragma("vm:never-inline")
-Future<void> _loadLibrary(_LibraryPrefix prefix) {
-  return new Future<void>(() {
-    prefix._setLoaded();
-  });
-}
-
-@pragma("vm:entry-point")
-@pragma("vm:never-inline")
-void _checkLoaded(_LibraryPrefix prefix) {
-  if (!prefix._isLoaded()) {
-    throw new _DeferredNotLoadedError(prefix);
-  }
+  bool isLoaded() => true;
+
+  loadLibrary() => new Future.value(true);
 }

sdk_nnbd/lib/_internal/vm/lib/lib_prefix.dart

@@ -11,32 +11,7 @@ class _LibraryPrefix {
     throw "Unreachable";
   }
 
-  bool _isLoaded() native "LibraryPrefix_isLoaded";
-  void _setLoaded() native "LibraryPrefix_setLoaded";
-}
-
-class _DeferredNotLoadedError extends Error implements NoSuchMethodError {
-  _LibraryPrefix prefix;
-
-  _DeferredNotLoadedError(this.prefix);
-
-  String toString() {
-    return "Deferred library $prefix was not loaded.";
-  }
-}
-
-@pragma("vm:entry-point")
-@pragma("vm:never-inline")
-Future<void> _loadLibrary(_LibraryPrefix prefix) {
-  return new Future<void>(() {
-    prefix._setLoaded();
-  });
-}
-
-@pragma("vm:entry-point")
-@pragma("vm:never-inline")
-void _checkLoaded(_LibraryPrefix prefix) {
-  if (!prefix._isLoaded()) {
-    throw new _DeferredNotLoadedError(prefix);
-  }
+  bool isLoaded() => true;
+
+  loadLibrary() => new Future.value(true);
 }