[ddc] Updating representation for virtual and lazy fields.

This restructures all fields as accessor/value-store pairs, providing a level of indirection required for hot reload.

Major updates include:
- All fields (top-level, lazy, virtual, etc.) now have a value store (represented as a private top-level symbol). The value store is initialized on first access for the initializer.
- Lazy value stores are prefixed with '_#v_' to indicate that they are not replaced on a hot reload.
- `declareClass` and `declareTopLevelProperties` are introduced to append classes/members to libraries. These functions extend the 'original' entity/class with fields introduced by a properties object, ignoring the special lazy value stores mentioned above.
- `defineLazy` is replaced with the above operations.
- Virtual/instance fields are still initialized by inside their constructor on first load (so their getter forwards to its value store). On hot reload, however, uninitialized fields are lazily initialized.
- Final fields now use a sentinel value to check for late initialization errors during the initialization loop.
- The JS AST is extended to support class properties.

Change-Id: I5cc3548477d83897273f3b993b304a804754ec0e
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/386971
Reviewed-by: Nicholas Shahan <[email protected]>

Author: Markzipan

pkg/dev_compiler/lib/src/js_ast/nodes.dart

@@ -1802,8 +1802,11 @@ class ObjectInitializer extends Expression {
 class Property extends Node {
   final Expression name;
   final Expression value;
+  final bool isStatic;
+  final bool isClassProperty;
 
-  Property(this.name, this.value);
+  Property(this.name, this.value,
+      {this.isStatic = false, this.isClassProperty = false});
 
   @override
   T accept<T>(NodeVisitor<T> visitor) => visitor.visitProperty(this);
@@ -1815,7 +1818,8 @@ class Property extends Node {
   }
 
   @override
-  Property _clone() => Property(name, value);
+  Property _clone() => Property(name, value,
+      isStatic: isStatic, isClassProperty: isClassProperty);
 }
 
 // TODO(jmesserly): parser does not support this yet.
@@ -1925,9 +1929,9 @@ class ClassDeclaration extends Statement {
 class ClassExpression extends Expression {
   final Identifier name;
   final Expression? heritage;
-  final List<Method> methods;
+  final List<Property> properties;
 
-  ClassExpression(this.name, this.heritage, this.methods);
+  ClassExpression(this.name, this.heritage, this.properties);
 
   @override
   T accept<T>(NodeVisitor<T> visitor) => visitor.visitClassExpression(this);
@@ -1936,7 +1940,7 @@ class ClassExpression extends Expression {
   void visitChildren(NodeVisitor visitor) {
     name.accept(visitor);
     heritage?.accept(visitor);
-    for (Method element in methods) {
+    for (Property element in properties) {
       element.accept(visitor);
     }
   }
@@ -1945,7 +1949,7 @@ class ClassExpression extends Expression {
   ClassDeclaration toStatement() => ClassDeclaration(this);
 
   @override
-  ClassExpression _clone() => ClassExpression(name, heritage, methods);
+  ClassExpression _clone() => ClassExpression(name, heritage, properties);
 
   @override
   int get precedenceLevel => PRIMARY_LOW_PRECEDENCE;
@@ -1957,8 +1961,13 @@ class Method extends Node implements Property {
   final Fun function;
   final bool isGetter;
   final bool isSetter;
+
+  @override
   final bool isStatic;
 
+  @override
+  final bool isClassProperty = false;
+
   Method(this.name, this.function,
       {this.isGetter = false, this.isSetter = false, this.isStatic = false}) {
     assert(!isGetter || function.params.isEmpty);
@@ -2121,6 +2130,8 @@ class InterpolatedMethod extends Expression
   @override
   bool get isStatic => throw _unsupported;
   @override
+  bool get isClassProperty => throw _unsupported;
+  @override
   Fun get function => throw _unsupported;
   Error get _unsupported =>
       UnsupportedError('$runtimeType does not support this member.');
@@ -2561,13 +2572,13 @@ abstract class Transformer extends BaseVisitor<Node> {
   Node visitClassExpression(ClassExpression node) {
     final name = visit<Identifier>(node.name);
     final heritage = visitNullable<Expression>(node.heritage);
-    final methods = visitList<Method>(node.methods);
+    final properties = visitList<Property>(node.properties);
     if (isUnchanged(name, node.name) &&
         isUnchanged(heritage, node.heritage) &&
-        isUnchangedList(methods, node.methods)) {
+        isUnchangedList(properties, node.properties)) {
       return node;
     }
-    return ClassExpression(name, heritage, methods);
+    return ClassExpression(name, heritage, properties);
   }
 
   @override

pkg/dev_compiler/lib/src/js_ast/printer.dart

@@ -1149,11 +1149,21 @@ class Printer implements NodeVisitor {
 
   @override
   void visitProperty(Property node) {
+    if (node.isStatic) {
+      out('static ');
+    }
     propertyNameOut(node.name);
-    out(':');
+    if (node.isClassProperty) {
+      out(' =');
+    } else {
+      out(':');
+    }
     spaceOut();
     visitNestedExpression(node.value, ASSIGNMENT,
         newInForInit: false, newAtStatementBegin: false);
+    if (node.isClassProperty) {
+      out(';');
+    }
   }
 
   @override
@@ -1198,13 +1208,13 @@ class Printer implements NodeVisitor {
       visit(node.heritage!);
     }
     spaceOut();
-    if (node.methods.isNotEmpty) {
+    if (node.properties.isNotEmpty) {
       out('{');
       lineOut();
       indentMore();
-      for (var method in node.methods) {
+      for (var property in node.properties) {
         indent();
-        visit(method);
+        visit(property);
         lineOut();
       }
       indentLess();
@@ -1503,7 +1513,7 @@ class VarCollector extends BaseVisitorVoid {
   void visitClassExpression(ClassExpression node) {
     // Note that we don't bother collecting the name of the class.
     node.heritage?.accept(this);
-    for (Method method in node.methods) {
+    for (Property method in node.properties) {
       method.accept(this);
     }
   }
@@ -1813,7 +1823,7 @@ abstract class VariableDeclarationVisitor extends BaseVisitorVoid {
   void visitClassExpression(ClassExpression node) {
     declare(node.name);
     node.heritage?.accept(this);
-    for (Method element in node.methods) {
+    for (Property element in node.properties) {
       element.accept(this);
     }
   }

pkg/dev_compiler/lib/src/js_ast/template.dart

@@ -726,7 +726,8 @@ class InstantiatorGeneratorVisitor implements NodeVisitor<Instantiator> {
   Instantiator<Property> visitProperty(Property node) {
     var makeName = visit(node.name) as Instantiator<Expression>;
     var makeValue = visit(node.value) as Instantiator<Expression>;
-    return (arguments) => Property(makeName(arguments), makeValue(arguments));
+    return (arguments) => Property(makeName(arguments), makeValue(arguments),
+        isStatic: node.isStatic, isClassProperty: node.isClassProperty);
   }
 
   @override
@@ -756,13 +757,13 @@ class InstantiatorGeneratorVisitor implements NodeVisitor<Instantiator> {
 
   @override
   Instantiator<ClassExpression> visitClassExpression(ClassExpression node) {
-    var makeMethods = node.methods.map(visitSplayableExpression).toList();
+    var makeProperties = node.properties.map(visitSplayableExpression).toList();
     var makeName = visit(node.name) as Instantiator<Identifier>;
     var makeHeritage =
         visitNullable(node.heritage) as Instantiator<Expression?>;
 
     return (arguments) => ClassExpression(makeName(arguments),
-        makeHeritage(arguments), splayNodes(makeMethods, arguments));
+        makeHeritage(arguments), splayNodes(makeProperties, arguments));
   }
 
   @override