Added comstruction and validation of symbol table, addressed CR comments

Author: Anna Gringauze

dwds/lib/src/debugging/metadata/module_symbols.dart

@@ -7,15 +7,15 @@
 // Dart debug symbol information stored by DDC.
 //
 // The data format below stores descriptions of dart code objects and their
-// mapping to JS that is generated by DDC. Every field, except ids, descrbes
+// mapping to JS that is generated by DDC. Every field, except ids, describes
 // dart.
 
 // Note that 'localId' and 'scopeId' combine into a unique id that is used for
 // object lookup and mapping between JS and dart concepts. As a result, it
-// needs to be either stored or easly computed for each corresponding JS object
+// needs to be either stored or easily computed for each corresponding JS object
 // created by DDC, so the debugger is able to look up dart symbol from JS ones.
 //
-// For example, to detect all dart variables in current scope and display
+// For example, to detect all dart variables in the current scope and display
 // their values, the debugger can do the following:
 //
 // - map current JS location to dart location using source maps
@@ -83,6 +83,10 @@ class SemanticVersion {
   }
 }
 
+/// Base class for a symbol table element.
+///
+/// Symbol tables and its elements are stored by the compiler using
+/// [toJson] method, and are read from json using `fromJson` constructors.
 abstract class SymbolTableElement {
   Map<String, dynamic> toJson();
 }
@@ -168,7 +172,6 @@ class ModuleSymbols implements SymbolTableElement {
 
     _setValueIfNotNull(json, 'version', version);
     _setValueIfNotNull(json, 'moduleName', moduleName);
-
     _setObjectListIfNotNull(json, 'libraries', libraries);
     _setObjectListIfNotNull(json, 'scripts', scripts);
     _setObjectListIfNotNull(json, 'classes', classes);
@@ -195,7 +198,7 @@ class Symbol implements SymbolTableElement {
   /// '<scope id>|<js name>'
   ///
   /// Where scope refers to a Library, Class, Function, or Scope.
-  String get id => '$scopeId|$localId';
+  String get id => scopeId == null ? localId : '$scopeId|$localId';
 
   /// Source location of the symbol.
   SourceLocation location;
@@ -316,8 +319,8 @@ class ClassSymbol extends ScopeSymbol implements TypeSymbol {
   /// A list of interface types for this class.
   List<String> interfaceIds;
 
-  /// Type parameters for this class.
-  List<String> typeParameters;
+  /// Mapping of type parameter dart names to JS names.
+  Map<String, String> typeParameters;
 
   /// Library that contains this class.
   String get libraryId => scopeId;
@@ -359,9 +362,8 @@ class ClassSymbol extends ScopeSymbol implements TypeSymbol {
     isAbstract = _createValue(json['isAbstract']);
     isConst = _createValue(json['isConst']);
     superClassId = _createValue(json['superClassId']);
-
     interfaceIds = _createValueList(json['interfaceIds']);
-    typeParameters = _createValueList(json['typeParameters']);
+    typeParameters = _createValueMap(json['typeParameters']);
   }
 
   @override
@@ -372,7 +374,6 @@ class ClassSymbol extends ScopeSymbol implements TypeSymbol {
     _setValueIfNotNull(json, 'isAbstract', isAbstract);
     _setValueIfNotNull(json, 'isConst', isConst);
     _setValueIfNotNull(json, 'superClassId', superClassId);
-
     _setValueIfNotNull(json, 'interfaceIds', interfaceIds);
     _setValueIfNotNull(json, 'typeParameters', typeParameters);
 
@@ -381,8 +382,8 @@ class ClassSymbol extends ScopeSymbol implements TypeSymbol {
 }
 
 class FunctionTypeSymbol extends Symbol implements TypeSymbol {
-  /// Type parameters for this function.
-  List<String> typeParameters;
+  /// Mapping of dart type parameter names to JS names.
+  Map<String, String> typeParameters;
 
   /// Types for positional parameters for this function.
   List<String> parameterTypeIds;
@@ -409,26 +410,23 @@ class FunctionTypeSymbol extends Symbol implements TypeSymbol {
 
   FunctionTypeSymbol.fromJson(Map<String, dynamic> json)
       : super.fromJson(json) {
-    typeParameters = _createValueList(json['typeParameters']);
     parameterTypeIds = _createValueList(json['parameterTypeIds']);
     optionalParameterTypeIds =
         _createValueList(json['optionalParameterTypeIds']);
-
-    namedParameterTypeIds = _createObject(json['namedParameterTypeIds'],
-        (json) => Map<String, String>.from(json));
+    namedParameterTypeIds = _createValueMap(json['namedParameterTypeIds']);
+    typeParameters = _createValueMap(json['typeParameters']);
     returnTypeId = _createValue(json['returnTypeId']);
   }
 
   @override
   Map<String, dynamic> toJson() {
     final json = super.toJson();
 
-    _setValueIfNotNull(json, 'typeParameters', typeParameters);
     _setValueIfNotNull(json, 'parameterTypeIds', parameterTypeIds);
     _setValueIfNotNull(
         json, 'optionalParameterTypeIds', optionalParameterTypeIds);
-
     _setValueIfNotNull(json, 'namedParameterTypeIds', namedParameterTypeIds);
+    _setValueIfNotNull(json, 'typeParameters', typeParameters);
     _setValueIfNotNull(json, 'returnTypeId', returnTypeId);
 
     return json;
@@ -524,17 +522,14 @@ class LibrarySymbol extends ScopeSymbol {
     List<String> scopeIds,
   }) : super(
           localId: uri,
-          scopeId: null,
           variableIds: variableIds,
           scopeIds: scopeIds,
-          location: null,
         );
 
   LibrarySymbol.fromJson(Map<String, dynamic> json) : super.fromJson(json) {
-    name = _createValue(json['name'], ifNull: '');
+    name = _createValue(json['name']);
     uri = _createValue(json['uri']);
     scriptIds = _createValueList(json['scriptIds']);
-
     dependencies = _createObjectList(
         json['dependencies'], (json) => LibraryDependency.fromJson(json));
   }
@@ -544,10 +539,8 @@ class LibrarySymbol extends ScopeSymbol {
     final json = super.toJson();
 
     _setValueIfNotNull(json, 'name', name);
-    _setValueIfNotNull(json, 'id', id);
     _setValueIfNotNull(json, 'uri', uri);
     _setValueIfNotNull(json, 'scriptIds', scriptIds);
-
     _setObjectListIfNotNull(json, 'dependencies', dependencies);
 
     return json;
@@ -603,24 +596,31 @@ class Script implements SymbolTableElement {
   /// This can be just an integer. The mapping from JS to dart script
   /// happens using the source map. The id is only used for references
   /// in other elements.
-  String id;
+  String localId;
+
+  String libraryId;
+
+  String get id => '$libraryId|$localId';
 
   Script({
     this.uri,
-    this.id,
+    this.localId,
+    this.libraryId,
   });
 
   Script.fromJson(Map<String, dynamic> json) {
     uri = _createValue(json['uri']);
-    id = _createValue(json['id']);
+    localId = _createValue(json['localId']);
+    libraryId = _createValue(json['libraryId']);
   }
 
   @override
   Map<String, dynamic> toJson() {
     final json = <String, dynamic>{};
 
     _setValueIfNotNull(json, 'uri', uri);
-    _setValueIfNotNull(json, 'id', id);
+    _setValueIfNotNull(json, 'localId', localId);
+    _setValueIfNotNull(json, 'libraryId', libraryId);
 
     return json;
   }
@@ -697,10 +697,9 @@ class SourceLocation implements SymbolTableElement {
   }
 }
 
-List<T> _createObjectList<T>(
+List<T> _createObjectList<T extends SymbolTableElement>(
     dynamic json, T Function(Map<String, dynamic>) creator) {
-  if (json == null) return null;
-
+  if (json == null) return [];
   if (json is List) {
     return json.map((e) => _createObject(e, creator)).toList();
   }
@@ -709,7 +708,6 @@ List<T> _createObjectList<T>(
 
 T _createObject<T>(dynamic json, T Function(Map<String, dynamic>) creator) {
   if (json == null) return null;
-
   if (json is Map<String, dynamic>) {
     return creator(json);
   }
@@ -718,8 +716,7 @@ T _createObject<T>(dynamic json, T Function(Map<String, dynamic>) creator) {
 
 List<T> _createValueList<T>(dynamic json,
     {T ifNull, T Function(String) parse}) {
-  if (json == null) return null;
-
+  if (json == null) return [];
   if (json is List) {
     return json
         .map((e) => _createValue<T>(e, ifNull: ifNull, parse: parse))
@@ -728,12 +725,14 @@ List<T> _createValueList<T>(dynamic json,
   throw ArgumentError('Not a list: $json');
 }
 
+Map<String, T> _createValueMap<T>(dynamic json) {
+  if (json == null) return {};
+  return Map<String, T>.from(json as Map<String, dynamic>);
+}
+
 T _createValue<T>(dynamic json, {T ifNull, T Function(String) parse}) {
   if (json == null) return ifNull;
-
-  if (json is T) {
-    return json;
-  }
+  if (json is T) return json;
   if (json is String && parse != null) {
     return parse(json);
   }