Remove writeOptionalReference

References can be null --- it's written as the byte [0].
Thus in the null case it would before be [0] and now be [0].
In the non-null case it would before be [1, xyz] (1 for Tag.Something
and xyz for the actual, now positive, uint30). Now it would be [xyz].

Change-Id: Ibc08d3afb7275b0429a4d6c5e667fbd381121489
Reviewed-on: https://dart-review.googlesource.com/c/85394
Reviewed-by: Kevin Millikin <kmillikin@google.com>
Commit-Queue: Jens Johansen <jensj@google.com>

pkg/kernel/binary.md

@@ -131,7 +131,7 @@ type CanonicalName {
 
 type ComponentFile {
   UInt32 magic = 0x90ABCDEF;
-  UInt32 formatVersion = 14;
+  UInt32 formatVersion = 15;
   Library[] libraries;
   UriSource sourceMap;
   List<CanonicalName> canonicalNames;
@@ -373,8 +373,8 @@ type Procedure extends Member {
   Name name;
   List<Expression> annotations;
   // Only present if the 'isForwardingStub' flag is set.
-  Option<MemberReference> forwardingStubSuperTarget;
-  Option<MemberReference> forwardingStubInterfaceTarget;
+  MemberReference forwardingStubSuperTarget; // May be NullReference.
+  MemberReference forwardingStubInterfaceTarget; // May be NullReference.
   // Can only be absent if abstract, but tag is there anyway.
   Option<FunctionNode> function;
 }
@@ -886,7 +886,7 @@ type StringConstant extends Constant {
 
 type SymbolConstant extends Constant {
   Byte tag = 5;
-  Option<LibraryReference> library;
+  LibraryReference library; // May be NullReference.
   StringReference name;
 }
 

pkg/kernel/lib/binary/ast_from_binary.dart

@@ -216,10 +216,7 @@ class BinaryBuilder {
       case ConstantTag.StringConstant:
         return new StringConstant(readStringReference());
       case ConstantTag.SymbolConstant:
-        Reference libraryReference;
-        if (readAndCheckOptionTag()) {
-          libraryReference = readLibraryReference();
-        }
+        Reference libraryReference = readLibraryReference(allowNull: true);
         return new SymbolConstant(readStringReference(), libraryReference);
       case ConstantTag.MapConstant:
         final DartType keyType = readDartType();
@@ -1113,9 +1110,9 @@ class BinaryBuilder {
         (kind == ProcedureKind.Factory && functionNodeSize <= 50) ||
             _disableLazyReading;
     var forwardingStubSuperTargetReference =
-        readAndCheckOptionTag() ? readMemberReference() : null;
+        readMemberReference(allowNull: true);
     var forwardingStubInterfaceTargetReference =
-        readAndCheckOptionTag() ? readMemberReference() : null;
+        readMemberReference(allowNull: true);
     var function = readFunctionNodeOption(!readFunctionNodeNow, endOffset);
     var transformerFlags = getAndResetTransformerFlags();
     assert(((_) => true)(debugPath.removeLast()));

pkg/kernel/lib/binary/ast_to_binary.dart

@@ -203,7 +203,7 @@ class BinaryPrinter implements Visitor<void>, BinarySink {
       writeStringReference(constant.value);
     } else if (constant is SymbolConstant) {
       writeByte(ConstantTag.SymbolConstant);
-      writeOptionalReference(constant.libraryReference);
+      writeNullAllowedReference(constant.libraryReference);
       writeStringReference(constant.name);
     } else if (constant is MapConstant) {
       writeByte(ConstantTag.MapConstant);
@@ -459,15 +459,6 @@ class BinaryPrinter implements Visitor<void>, BinarySink {
     }
   }
 
-  void writeOptionalReference(Reference ref) {
-    if (ref == null) {
-      writeByte(Tag.Nothing);
-    } else {
-      writeByte(Tag.Something);
-      writeNonNullReference(ref);
-    }
-  }
-
   void writeLinkTable(Component component) {
     _binaryOffsetForLinkTable = getBufferOffset();
     writeList(_canonicalNameList, writeCanonicalNameEntry);
@@ -1107,8 +1098,8 @@ class BinaryPrinter implements Visitor<void>, BinarySink {
     writeByte(node.flags);
     writeName(node.name ?? _emptyName);
     writeAnnotationList(node.annotations);
-    writeOptionalReference(node.forwardingStubSuperTargetReference);
-    writeOptionalReference(node.forwardingStubInterfaceTargetReference);
+    writeNullAllowedReference(node.forwardingStubSuperTargetReference);
+    writeNullAllowedReference(node.forwardingStubInterfaceTargetReference);
     writeOptionalFunctionNode(node.function);
     leaveScope(memberScope: true);
 

pkg/kernel/lib/binary/tag.dart

@@ -136,7 +136,7 @@ class Tag {
   /// Internal version of kernel binary format.
   /// Bump it when making incompatible changes in kernel binaries.
   /// Keep in sync with runtime/vm/kernel_binary.h, pkg/kernel/binary.md.
-  static const int BinaryFormatVersion = 14;
+  static const int BinaryFormatVersion = 15;
 }
 
 abstract class ConstantTag {

runtime/vm/compiler/frontend/constant_evaluator.cc

@@ -1169,12 +1169,11 @@ const Array& ConstantHelper::ReadConstantTable() {
         break;
       }
       case kSymbolConstant: {
-        Tag initializer_tag = helper_.ReadTag();
-        if (initializer_tag == kSomething) {
-          const NameIndex index = helper_.ReadCanonicalNameReference();
-          temp_library_ = H.LookupLibraryByKernelLibrary(index);
-        } else {
+        const NameIndex index = helper_.ReadCanonicalNameReference();
+        if (index == -1) {
           temp_library_ = Library::null();
+        } else {
+          temp_library_ = H.LookupLibraryByKernelLibrary(index);
         }
         const String& symbol =
             H.DartIdentifier(temp_library_, helper_.ReadStringReference());

runtime/vm/compiler/frontend/kernel_translation_helper.cc

@@ -1024,20 +1024,17 @@ void ProcedureHelper::ReadUntilExcluding(Field field) {
     }
       /* Falls through */
     case kForwardingStubSuperTarget:
-      if (helper_->ReadTag() == kSomething) {
-        forwarding_stub_super_target_ = helper_->ReadCanonicalNameReference();
-      }
+      forwarding_stub_super_target_ = helper_->ReadCanonicalNameReference();
       if (++next_read_ == field) return;
       /* Falls through */
     case kForwardingStubInterfaceTarget:
-      if (helper_->ReadTag() == kSomething) {
-        helper_->ReadCanonicalNameReference();
-      }
+      helper_->ReadCanonicalNameReference();
       if (++next_read_ == field) return;
       /* Falls through */
     case kFunction:
-      if (helper_->ReadTag() == kSomething)
+      if (helper_->ReadTag() == kSomething) {
         helper_->SkipFunctionNode();  // read function node.
+      }
       if (++next_read_ == field) return;
       /* Falls through */
     case kEnd:

runtime/vm/kernel_binary.h

@@ -17,7 +17,7 @@ namespace kernel {
 // package:kernel/binary.md.
 
 static const uint32_t kMagicProgramFile = 0x90ABCDEFu;
-static const uint32_t kBinaryFormatVersion = 14;
+static const uint32_t kBinaryFormatVersion = 15;
 
 // Keep in sync with package:kernel/lib/binary/tag.dart
 #define KERNEL_TAG_LIST(V)                                                     \