[kernel] Add field for instantiate-to-bounds algorithm in TypeParameter.

Change-Id: Idd1859b378080f01dc5d5078ee0960021c1689b6
Reviewed-on: https://dart-review.googlesource.com/48424
Reviewed-by: Régis Crelier <regis@google.com>
Reviewed-by: Dmitry Stefantsov <dmitryas@google.com>

pkg/kernel/binary.md

@@ -1200,6 +1200,7 @@ type TypeParameter {
   List<Expression> annotations;
   StringReference name; // Cosmetic, may be empty, not unique.
   DartType bound; // 'dynamic' if no explicit bound was given.
+  Option<DartType> defaultType; // type used when the parameter is not passed
 }
 
 ```

pkg/kernel/lib/ast.dart

@@ -5220,6 +5220,13 @@ class TypeParameter extends TreeNode {
   /// be set to the root class for type parameters without an explicit bound.
   DartType bound;
 
+  /// The default value of the type variable. It is used to provide the
+  /// corresponding missing type argument in type annotations and as the
+  /// fall-back type value in type inference at compile time. At run time,
+  /// [defaultType] is used by the backends in place of the missing type
+  /// argument of a dynamic invocation of a generic function.
+  DartType defaultType;
+
   TypeParameter([this.name, this.bound]);
 
   // Must match serialized bit positions.

pkg/kernel/lib/binary/ast_from_binary.dart

@@ -1750,6 +1750,7 @@ class BinaryBuilder {
     node.annotations = readAnnotationList(node);
     node.name = readStringOrNullIfEmpty();
     node.bound = readDartType();
+    node.defaultType = readDartTypeOption();
   }
 
   Arguments readArguments() {

pkg/kernel/lib/binary/ast_to_binary.dart

@@ -1716,6 +1716,7 @@ class BinaryPrinter implements Visitor<void>, BinarySink {
     writeAnnotationList(node.annotations);
     writeStringReference(node.name ?? '');
     writeNode(node.bound);
+    writeOptionalNode(node.defaultType);
   }
 
   // ================================================================

pkg/kernel/lib/clone.dart

@@ -470,6 +470,9 @@ class CloneVisitor implements TreeVisitor {
     var newNode = new TypeParameter(node.name);
     typeSubstitution[node] = new TypeParameterType(newNode);
     newNode.bound = visitType(node.bound);
+    if (node.defaultType != null) {
+      newNode.defaultType = visitType(node.defaultType);
+    }
     return newNode..flags = node.flags;
   }
 

pkg/kernel/lib/text/ast_to_text.dart

@@ -1842,6 +1842,10 @@ class Printer extends Visitor<Null> {
     writeWord(getTypeParameterName(node));
     writeSpaced('extends');
     writeType(node.bound);
+    if (node.defaultType != null) {
+      writeSpaced('=');
+      writeType(node.defaultType);
+    }
   }
 
   visitConstantExpression(ConstantExpression node) {

runtime/vm/compiler/frontend/kernel_binary_flowgraph.cc

@@ -80,6 +80,32 @@ void FunctionNodeHelper::ReadUntilExcluding(Field field) {
   }
 }
 
+void TypeParameterHelper::ReadUntilExcluding(Field field) {
+  for (; next_read_ < field; ++next_read_) {
+    switch (next_read_) {
+      case kFlags:
+        flags_ = builder_->ReadFlags();
+        break;
+      case kAnnotations:
+        builder_->SkipListOfExpressions();  // read annotations.
+        break;
+      case kName:
+        name_index_ = builder_->ReadStringReference();  // read name index.
+        break;
+      case kBound:
+        builder_->SkipDartType();
+        break;
+      case kDefaultType:
+        if (builder_->ReadTag() == kSomething) {
+          builder_->SkipDartType();
+        }
+        break;
+      case kEnd:
+        return;
+    }
+  }
+}
+
 void VariableDeclarationHelper::ReadUntilExcluding(Field field) {
   if (field <= next_read_) return;
 
@@ -1189,10 +1215,14 @@ void StreamingScopeBuilder::VisitFunctionNode() {
   intptr_t list_length =
       builder_->ReadListLength();  // read type_parameters list length.
   for (intptr_t i = 0; i < list_length; ++i) {
-    builder_->ReadFlags();              // read flags.
-    builder_->SkipListOfExpressions();  // read annotations.
-    builder_->SkipStringReference();    // read ith name index.
+    TypeParameterHelper helper(builder_);
+    helper.ReadUntilExcludingAndSetJustRead(TypeParameterHelper::kBound);
     VisitDartType();                    // read ith bound.
+    helper.ReadUntilExcludingAndSetJustRead(TypeParameterHelper::kDefaultType);
+    if (builder_->ReadTag() == kSomething) {
+      VisitDartType();  // read ith default type.
+    }
+    helper.Finish();
   }
   function_node_helper.SetJustRead(FunctionNodeHelper::kTypeParameters);
 
@@ -1977,10 +2007,14 @@ void StreamingScopeBuilder::VisitFunctionType(bool simple) {
     intptr_t list_length =
         builder_->ReadListLength();  // read type_parameters list length.
     for (int i = 0; i < list_length; ++i) {
-      builder_->SkipFlags();              // read flags.
-      builder_->SkipListOfExpressions();  // read annotations.
-      builder_->SkipStringReference();    // read string index (name).
-      VisitDartType();                    // read dart type.
+      TypeParameterHelper helper(builder_);
+      helper.ReadUntilExcludingAndSetJustRead(TypeParameterHelper::kBound);
+      VisitDartType();  // read bound.
+      helper.ReadUntilExcludingAndSetJustRead(TypeParameterHelper::kDefaultType);
+      if (builder_->ReadTag() == kSomething) {
+        VisitDartType();  // read default type.
+      }
+      helper.Finish();
     }
     builder_->ReadUInt();  // read required parameter count.
     builder_->ReadUInt();  // read total parameter count.
@@ -4569,10 +4603,11 @@ Fragment StreamingFlowGraphBuilder::BuildArgumentTypeChecks(
     }
     TypeParameter& forwarding_param = TypeParameter::Handle(Z);
     for (intptr_t i = 0; i < num_type_params; ++i) {
-      ReadFlags();                                         // skip flags
-      SkipListOfExpressions();                             // skip annotations
-      String& name = H.DartSymbolObfuscate(ReadStringReference());  // read name
+      TypeParameterHelper helper(this);
+      helper.ReadUntilExcludingAndSetJustRead(TypeParameterHelper::kBound);
+      String& name = H.DartSymbolObfuscate(helper.name_index_);
       AbstractType& bound = T.BuildType();                 // read bound
+      helper.Finish();
 
       if (forwarding_target != NULL) {
         forwarding_param ^= forwarding_params.TypeAt(i);
@@ -5488,10 +5523,8 @@ void StreamingFlowGraphBuilder::SkipListOfVariableDeclarations() {
 void StreamingFlowGraphBuilder::SkipTypeParametersList() {
   intptr_t list_length = ReadListLength();  // read list length.
   for (intptr_t i = 0; i < list_length; ++i) {
-    SkipFlags();              // read ith flags.
-    SkipListOfExpressions();  // read annotations.
-    SkipStringReference();    // read ith name index.
-    SkipDartType();           // read ith bound.
+    TypeParameterHelper helper(this);
+    helper.Finish();
   }
 }
 
@@ -9603,15 +9636,14 @@ void StreamingFlowGraphBuilder::LoadAndSetupTypeParameters(
   {
     AlternativeReadingScope alt(reader_);
     for (intptr_t i = 0; i < type_parameter_count; i++) {
-      SkipFlags();
-      SkipListOfExpressions();  // read annotations.
+      TypeParameterHelper helper(this);
+      helper.Finish();
       parameter = TypeParameter::New(
           set_on_class ? *active_class->klass : Class::Handle(Z),
           parameterized_function, i,
-          H.DartSymbolObfuscate(ReadStringReference()),  // read ith name index.
+          H.DartSymbolObfuscate(helper.name_index_),  // read ith name index.
           null_bound, TokenPosition::kNoSource);
       type_parameters.SetTypeAt(i, parameter);
-      SkipDartType();  // read guard.
     }
   }
 
@@ -9629,9 +9661,8 @@ void StreamingFlowGraphBuilder::LoadAndSetupTypeParameters(
 
   // Step b) Fill in the bounds of all [TypeParameter]s.
   for (intptr_t i = 0; i < type_parameter_count; i++) {
-    SkipFlags();
-    SkipListOfExpressions();  // read annotations.
-    SkipStringReference();    // read ith name index.
+    TypeParameterHelper helper(this);
+    helper.ReadUntilExcludingAndSetJustRead(TypeParameterHelper::kBound);
 
     // TODO(github.com/dart-lang/kernel/issues/42): This should be handled
     // by the frontend.
@@ -9648,6 +9679,8 @@ void StreamingFlowGraphBuilder::LoadAndSetupTypeParameters(
       }
       parameter.set_bound(bound);
     }
+
+    helper.Finish();
   }
 }
 

runtime/vm/compiler/frontend/kernel_binary_flowgraph.h

@@ -76,11 +76,51 @@ class FunctionNodeHelper {
   intptr_t next_read_;
 };
 
-struct TypeParameterHelper {
+class TypeParameterHelper {
+ public:
+  enum Field {
+    kStart,  // tag.
+    kFlags,
+    kAnnotations,
+    kName,
+    kBound,
+    kDefaultType,
+    kEnd,
+  };
+
   enum Flag {
     kIsGenericCovariantImpl = 1 << 0,
     kIsGenericCovariantInterface = 1 << 1
   };
+
+  explicit TypeParameterHelper(StreamingFlowGraphBuilder* builder) {
+    builder_ = builder;
+    next_read_ = kStart;
+  }
+
+  void ReadUntilIncluding(Field field) {
+    ReadUntilExcluding(static_cast<Field>(static_cast<int>(field) + 1));
+  }
+
+  void ReadUntilExcluding(Field field);
+
+  void SetNext(Field field) { next_read_ = field; }
+  void SetJustRead(Field field) { next_read_ = field + 1; }
+
+  void ReadUntilExcludingAndSetJustRead(Field field) {
+    ReadUntilExcluding(field);
+    SetJustRead(field);
+  }
+
+  void Finish() { ReadUntilExcluding(kEnd); }
+
+  TokenPosition position_;
+  uint8_t flags_;
+  StringIndex name_index_;
+
+ private:
+  StreamingFlowGraphBuilder* builder_;
+  intptr_t next_read_;
 };
 
 // Helper class that reads a kernel VariableDeclaration from binary.
@@ -1434,6 +1474,7 @@ class StreamingFlowGraphBuilder {
   friend class StreamingDartTypeTranslator;
   friend class StreamingScopeBuilder;
   friend class VariableDeclarationHelper;
+  friend class TypeParameterHelper;
 };
 
 class AlternativeScriptScope {