dwds/lib/src/debugging/instance.dart - third_party/dart-pkg - Git at Google

 // Copyright (c) 2019, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.

 import 'dart:math';

 import 'package:vm_service/vm_service.dart';
 import 'package:webkit_inspection_protocol/webkit_inspection_protocol.dart';

 import '../loaders/strategy.dart';
 import '../utilities/conversions.dart';
 import '../utilities/domain.dart';
 import '../utilities/objects.dart';
 import '../utilities/shared.dart';
 import 'debugger.dart';
 import 'metadata/class.dart';
 import 'metadata/function.dart';

 /// Contains a set of methods for getting [Instance]s and [InstanceRef]s.
 class InstanceHelper extends Domain {
   InstanceHelper(AppInspectorInterface appInspector, this.debugger) {
     inspector = appInspector;
   }

   final Debugger debugger;
   static final InstanceRef kNullInstanceRef =
       _primitiveInstanceRef(InstanceKind.kNull, null);

   /// Creates an [InstanceRef] for a primitive [RemoteObject].
   static InstanceRef _primitiveInstanceRef(
       String kind, RemoteObject? remoteObject) {
     final classRef = classRefFor('dart:core', kind);
     return InstanceRef(
         identityHashCode: dartIdFor(remoteObject?.value).hashCode,
         kind: kind,
         classRef: classRef,
         id: dartIdFor(remoteObject?.value))
       ..valueAsString = '${remoteObject?.value}';
   }

   /// Creates an [Instance] for a primitive [RemoteObject].
   Instance? _primitiveInstance(String kind, RemoteObject? remote) {
     final objectId = remote?.objectId;
     if (objectId == null) return null;
     return Instance(
         identityHashCode: objectId.hashCode,
         id: objectId,
         kind: kind,
         classRef: classRefFor('dart:core', kind))
       ..valueAsString = '${remote?.value}';
   }

   Instance? _stringInstanceFor(
       RemoteObject? remoteObject, int? offset, int? count) {
     // TODO(#777) Consider a way of not passing the whole string around (in the
     // ID) in order to find a substring.
     final objectId = remoteObject?.objectId;
     if (objectId == null) return null;
     final fullString = stringFromDartId(objectId);
     var preview = fullString;
     var truncated = false;
     if (offset != null || count != null) {
       truncated = true;
       final start = offset ?? 0;
       final end = count == null ? null : min(start + count, fullString.length);
       preview = fullString.substring(start, end);
     }
     return Instance(
         identityHashCode: createId().hashCode,
         kind: InstanceKind.kString,
         classRef: classRefForString,
         id: createId())
       ..valueAsString = preview
       ..valueAsStringIsTruncated = truncated
       ..length = fullString.length
       ..count = (truncated ? preview.length : null)
       ..offset = (truncated ? offset : null);
   }

   Future<Instance?> _closureInstanceFor(RemoteObject remoteObject) async {
     final objectId = remoteObject.objectId;
     if (objectId == null) return null;
     final result = Instance(
         kind: InstanceKind.kClosure,
         id: objectId,
         identityHashCode: remoteObject.objectId.hashCode,
         classRef: classRefForClosure);
     return result;
   }

   /// Create an [Instance] for the given [remoteObject].
   ///
   /// Does a remote eval to get instance information. Returns null if there
   /// isn't a corresponding instance. For enumerable objects, [offset] and
   /// [count] allow retrieving a sub-range of properties.
   Future<Instance?> instanceFor(RemoteObject? remoteObject,
       {int? offset, int? count}) async {
     final primitive = _primitiveInstanceOrNull(remoteObject, offset, count);
     if (primitive != null) {
       return primitive;
     }
     final objectId = remoteObject?.objectId;
     if (remoteObject == null || objectId == null) return null;

     // TODO: This is checking the JS object ID for the dart pattern we use for
     // VM objects, which seems wrong (and, we catch 'string' types above).
     if (isStringId(objectId)) {
       return _stringInstanceFor(remoteObject, offset, count);
     }

     final metaData = await ClassMetaData.metaDataFor(
         inspector.remoteDebugger, remoteObject, inspector);

     final classRef = metaData?.classRef;
     if (metaData == null || classRef == null) return null;
     if (metaData.jsName == 'Function') {
       return _closureInstanceFor(remoteObject);
     }

     final properties = await debugger.getProperties(objectId,
         offset: offset, count: count, length: metaData.length);
     if (metaData.isSystemList) {
       return await _listInstanceFor(
           classRef, remoteObject, properties, offset, count);
     } else if (metaData.isSystemMap) {
       return await _mapInstanceFor(
           classRef, remoteObject, properties, offset, count);
     } else {
       return await _plainInstanceFor(classRef, remoteObject, properties);
     }
   }

   /// If [remoteObject] represents a primitive, return an [Instance] for it,
   /// otherwise return null.
   Instance? _primitiveInstanceOrNull(
       RemoteObject? remoteObject, int? offset, int? count) {
     switch (remoteObject?.type ?? 'undefined') {
       case 'string':
         return _stringInstanceFor(remoteObject, offset, count);
       case 'number':
         return _primitiveInstance(InstanceKind.kDouble, remoteObject);
       case 'boolean':
         return _primitiveInstance(InstanceKind.kBool, remoteObject);
       case 'undefined':
         return _primitiveInstance(InstanceKind.kNull, remoteObject);
       default:
         return null;
     }
   }

   /// Create a bound field for [property] in an instance of [classRef].
   Future<BoundField> _fieldFor(Property property, ClassRef classRef) async {
     final instance = await _instanceRefForRemote(property.value);
     return BoundField(
         decl: FieldRef(
           // TODO(grouma) - Convert JS name to Dart.
           name: property.name,
           declaredType: InstanceRef(
               kind: InstanceKind.kType,
               classRef: instance?.classRef,
               identityHashCode: createId().hashCode,
               id: createId()),
           owner: classRef,
           // TODO(grouma) - Fill these in.
           isConst: false,
           isFinal: false,
           isStatic: false,
           id: createId(),
         ),
         value: instance);
   }

   /// Create a plain instance of [classRef] from [remoteObject] and the JS
   /// properties [properties].
   Future<Instance?> _plainInstanceFor(ClassRef classRef,
       RemoteObject remoteObject, List<Property> properties) async {
     final objectId = remoteObject.objectId;
     if (objectId == null) return null;
     final dartProperties = await _dartFieldsFor(properties, remoteObject);
     var boundFields = await Future.wait(
         dartProperties.map<Future<BoundField>>((p) => _fieldFor(p, classRef)));
     boundFields = boundFields
         .where((bv) => isDisplayableObject(bv.value))
         .toList()
       ..sort(_compareBoundFields);
     final result = Instance(
         kind: InstanceKind.kPlainInstance,
         id: objectId,
         identityHashCode: remoteObject.objectId.hashCode,
         classRef: classRef)
       ..fields = boundFields;
     return result;
   }

   int _compareBoundFields(BoundField a, BoundField b) {
     final aName = a.decl?.name;
     final bName = b.decl?.name;
     if (aName == null) return bName == null ? 0 : -1;
     if (bName == null) return 1;
     return aName.compareTo(bName);
   }

   /// The associations for a Dart Map or IdentityMap.
   Future<List<MapAssociation>> _mapAssociations(
       RemoteObject map, int? offset, int? count) async {
     // We do this in in awkward way because we want the keys and values, but we
     // can't return things by value or some Dart objects will come back as
     // values that we need to be RemoteObject, e.g. a List of int.
     final expression = '''
       function() {
         var sdkUtils = ${globalLoadStrategy.loadModuleSnippet}('dart_sdk').dart;
         var entries = sdkUtils.dloadRepl(this, "entries");
         entries = sdkUtils.dsendRepl(entries, "toList", []);
         function asKey(entry) {
           return sdkUtils.dloadRepl(entry, "key");
         }
         function asValue(entry) {
           return sdkUtils.dloadRepl(entry, "value");
         }
         return {
           keys: entries.map(asKey),
           values: entries.map(asValue)
         };
       }
     ''';
     final keysAndValues = await inspector.jsCallFunctionOn(map, expression, []);
     final keys = await inspector.loadField(keysAndValues, 'keys');
     final values = await inspector.loadField(keysAndValues, 'values');
     final keysInstance = await instanceFor(keys, offset: offset, count: count);
     final valuesInstance =
         await instanceFor(values, offset: offset, count: count);
     final associations = <MapAssociation>[];
     final keyElements = keysInstance?.elements;
     final valueElements = valuesInstance?.elements;
     if (keyElements != null && valueElements != null) {
       Map.fromIterables(keyElements, valueElements).forEach((key, value) {
         associations.add(MapAssociation(key: key, value: value));
       });
     }
     return associations;
   }

   /// Create a Map instance with class [classRef] from [remoteObject].
   Future<Instance?> _mapInstanceFor(
       ClassRef classRef,
       RemoteObject remoteObject,
       List<Property> _,
       int? offset,
       int? count) async {
     final objectId = remoteObject.objectId;
     if (objectId == null) return null;
     // Maps are complicated, do an eval to get keys and values.
     final associations = await _mapAssociations(remoteObject, offset, count);
     final length = (offset == null && count == null)
         ? associations.length
         : (await instanceRefFor(remoteObject))?.length;
     return Instance(
         identityHashCode: remoteObject.objectId.hashCode,
         kind: InstanceKind.kMap,
         id: objectId,
         classRef: classRef)
       ..length = length
       ..offset = offset
       ..count = (associations.length == length) ? null : associations.length
       ..associations = associations;
   }

   /// Create a List instance of [classRef] from [remoteObject] with the JS
   /// properties [properties].
   Future<Instance?> _listInstanceFor(
       ClassRef classRef,
       RemoteObject remoteObject,
       List<Property> properties,
       int? offset,
       int? count) async {
     final objectId = remoteObject.objectId;
     if (objectId == null) return null;

     /// TODO(annagrin): split into cases to make the logic clear.
     /// TODO(annagrin): make sure we use offset correctly.
     final numberOfProperties = _lengthOf(properties) ?? 0;
     final length = (offset == null && count == null)
         ? numberOfProperties
         : (await instanceRefFor(remoteObject))?.length;
     final indexed = properties.sublist(
         0, min(count ?? length ?? numberOfProperties, numberOfProperties));
     final fields = await Future.wait(indexed
         .map((property) async => await _instanceRefForRemote(property.value)));
     return Instance(
         identityHashCode: remoteObject.objectId.hashCode,
         kind: InstanceKind.kList,
         id: objectId,
         classRef: classRef)
       ..length = length
       ..elements = fields
       ..offset = offset
       ..count = (numberOfProperties == length) ? null : numberOfProperties;
   }

   /// Return the value of the length attribute from [properties], if present.
   ///
   /// This is only applicable to Lists or Maps, where we expect a length
   /// attribute. Even if a plain instance happens to have a length field, we
   /// don't use it to determine the properties to display.
   int? _lengthOf(List<Property> properties) {
     final lengthProperty = properties.firstWhere((p) => p.name == 'length');
     return lengthProperty.value?.value as int?;
   }

   /// Filter [allJsProperties] and return a list containing only those
   /// that correspond to Dart fields on [remoteObject].
   ///
   /// This only applies to objects with named fields, not Lists or Maps.
   Future<List<Property>> _dartFieldsFor(
       List<Property> allJsProperties, RemoteObject remoteObject) async {
     // An expression to find the field names from the types, extract both
     // private (named by symbols) and public (named by strings) and return them
     // as a comma-separated single string, so we can return it by value and not
     // need to make multiple round trips.
     //
     // For maps and lists it's more complicated. Treat the actual SDK versions
     // of these as special.
     final fieldNameExpression = '''function() {
       const sdk = ${globalLoadStrategy.loadModuleSnippet}("dart_sdk");
       const sdk_utils = sdk.dart;
       const fields = sdk_utils.getFields(sdk_utils.getType(this)) || [];
       if (!fields && (dart_sdk._interceptors.JSArray.is(this) ||
           dart_sdk._js_helper.InternalMap.is(this))) {
         // Trim off the 'length' property.
         const fields = allJsProperties.slice(0, allJsProperties.length -1);
         return fields.join(',');
       }
       const privateFields = sdk_utils.getOwnPropertySymbols(fields);
       const nonSymbolNames = privateFields
                             .map(sym => sym.description
                               .split('#').slice(-1)[0]);
       const publicFieldNames = sdk_utils.getOwnPropertyNames(fields);
       const symbolNames =  Object.getOwnPropertySymbols(this)
                             .map(sym => sym.description
                               .split('#').slice(-1)[0]
                               .split('.').slice(-1)[0]);
       return nonSymbolNames
         .concat(publicFieldNames)
         .concat(symbolNames).join(',');
     }
     ''';
     final allNames = (await inspector
             .jsCallFunctionOn(remoteObject, fieldNameExpression, []))
         .value as String;
     final names = allNames.split(',');
     // TODO(#761): Better support for large collections.
     return allJsProperties
         .where((property) => names.contains(property.name))
         .toList();
   }

   /// Create an InstanceRef for an object, which may be a RemoteObject, or may
   /// be something returned by value from Chrome, e.g. number, boolean, or
   /// String.
   Future<InstanceRef?> instanceRefFor(Object value) {
     final remote = value is RemoteObject
         ? value
         : RemoteObject({'value': value, 'type': _chromeType(value)});
     return _instanceRefForRemote(remote);
   }

   /// The Chrome type for a value.
   String? _chromeType(Object? value) {
     if (value == null) return null;
     if (value is String) return 'string';
     if (value is num) return 'number';
     if (value is bool) return 'boolean';
     if (value is Function) return 'function';
     return 'object';
   }

   /// Create an [InstanceRef] for the given Chrome [remoteObject].
   Future<InstanceRef?> _instanceRefForRemote(RemoteObject? remoteObject) async {
     // If we have a null result, treat it as a reference to null.
     if (remoteObject == null) {
       return kNullInstanceRef;
     }

     switch (remoteObject.type) {
       case 'string':
         final stringValue = remoteObject.value as String?;
         // TODO: Support truncation for long strings.
         // TODO(#777): dartIdFor() will return an ID containing the entire
         // string, even if we're truncating the string value here.
         return InstanceRef(
             identityHashCode: dartIdFor(remoteObject.value).hashCode,
             id: dartIdFor(remoteObject.value),
             classRef: classRefForString,
             kind: InstanceKind.kString)
           ..valueAsString = stringValue
           ..length = stringValue?.length;
       case 'number':
         return _primitiveInstanceRef(InstanceKind.kDouble, remoteObject);
       case 'boolean':
         return _primitiveInstanceRef(InstanceKind.kBool, remoteObject);
       case 'undefined':
         return _primitiveInstanceRef(InstanceKind.kNull, remoteObject);
       case 'object':
         final objectId = remoteObject.objectId;
         if (objectId == null) {
           return _primitiveInstanceRef(InstanceKind.kNull, remoteObject);
         }
         final metaData = await ClassMetaData.metaDataFor(
             inspector.remoteDebugger, remoteObject, inspector);
         if (metaData == null) return null;
         if (metaData.isSystemList) {
           return InstanceRef(
               kind: InstanceKind.kList,
               id: objectId,
               identityHashCode: remoteObject.objectId.hashCode,
               classRef: metaData.classRef)
             ..length = metaData.length;
         }
         if (metaData.isSystemMap) {
           return InstanceRef(
               kind: InstanceKind.kMap,
               id: objectId,
               identityHashCode: remoteObject.objectId.hashCode,
               classRef: metaData.classRef)
             ..length = metaData.length;
         }
         return InstanceRef(
             kind: InstanceKind.kPlainInstance,
             id: objectId,
             identityHashCode: remoteObject.objectId.hashCode,
             classRef: metaData.classRef);
       case 'function':
         final functionMetaData = await FunctionMetaData.metaDataFor(
             inspector.remoteDebugger, remoteObject);
         final objectId = remoteObject.objectId;
         if (objectId == null) {
           return _primitiveInstanceRef(InstanceKind.kNull, remoteObject);
         }
         return InstanceRef(
             kind: InstanceKind.kClosure,
             id: objectId,
             identityHashCode: remoteObject.objectId.hashCode,
             classRef: classRefForClosure)
           // TODO(grouma) - fill this in properly.
           ..closureFunction = FuncRef(
               name: functionMetaData.name,
               id: createId(),
               // TODO(alanknight): The right ClassRef
               owner: classRefForUnknown,
               isConst: false,
               isStatic: false,
               // TODO(annagrin): get information about getters and setters from symbols.
               // https://github.com/dart-lang/sdk/issues/46723
               implicit: false)
           ..closureContext = (ContextRef(length: 0, id: createId()));
       default:
         // Return null for an unsupported type. This is likely a JS construct.
         return null;
     }
   }
 }
	// Copyright (c) 2019, the Dart project authors. Please see the AUTHORS file
	// for details. All rights reserved. Use of this source code is governed by a
	// BSD-style license that can be found in the LICENSE file.

	import 'dart:math';

	import 'package:vm_service/vm_service.dart';
	import 'package:webkit_inspection_protocol/webkit_inspection_protocol.dart';

	import '../loaders/strategy.dart';
	import '../utilities/conversions.dart';
	import '../utilities/domain.dart';
	import '../utilities/objects.dart';
	import '../utilities/shared.dart';
	import 'debugger.dart';
	import 'metadata/class.dart';
	import 'metadata/function.dart';

	/// Contains a set of methods for getting [Instance]s and [InstanceRef]s.
	class InstanceHelper extends Domain {
	InstanceHelper(AppInspectorInterface appInspector, this.debugger) {
	inspector = appInspector;
	}

	final Debugger debugger;
	static final InstanceRef kNullInstanceRef =
	_primitiveInstanceRef(InstanceKind.kNull, null);

	/// Creates an [InstanceRef] for a primitive [RemoteObject].
	static InstanceRef _primitiveInstanceRef(
	String kind, RemoteObject? remoteObject) {
	final classRef = classRefFor('dart:core', kind);
	return InstanceRef(
	identityHashCode: dartIdFor(remoteObject?.value).hashCode,
	kind: kind,
	classRef: classRef,
	id: dartIdFor(remoteObject?.value))
	..valueAsString = '${remoteObject?.value}';
	}

	/// Creates an [Instance] for a primitive [RemoteObject].
	Instance? _primitiveInstance(String kind, RemoteObject? remote) {
	final objectId = remote?.objectId;
	if (objectId == null) return null;
	return Instance(
	identityHashCode: objectId.hashCode,
	id: objectId,
	kind: kind,
	classRef: classRefFor('dart:core', kind))
	..valueAsString = '${remote?.value}';
	}

	Instance? _stringInstanceFor(
	RemoteObject? remoteObject, int? offset, int? count) {
	// TODO(#777) Consider a way of not passing the whole string around (in the
	// ID) in order to find a substring.
	final objectId = remoteObject?.objectId;
	if (objectId == null) return null;
	final fullString = stringFromDartId(objectId);
	var preview = fullString;
	var truncated = false;
	if (offset != null \|\| count != null) {
	truncated = true;
	final start = offset ?? 0;
	final end = count == null ? null : min(start + count, fullString.length);
	preview = fullString.substring(start, end);
	}
	return Instance(
	identityHashCode: createId().hashCode,
	kind: InstanceKind.kString,
	classRef: classRefForString,
	id: createId())
	..valueAsString = preview
	..valueAsStringIsTruncated = truncated
	..length = fullString.length
	..count = (truncated ? preview.length : null)
	..offset = (truncated ? offset : null);
	}

	Future<Instance?> _closureInstanceFor(RemoteObject remoteObject) async {
	final objectId = remoteObject.objectId;
	if (objectId == null) return null;
	final result = Instance(
	kind: InstanceKind.kClosure,
	id: objectId,
	identityHashCode: remoteObject.objectId.hashCode,
	classRef: classRefForClosure);
	return result;
	}

	/// Create an [Instance] for the given [remoteObject].
	///
	/// Does a remote eval to get instance information. Returns null if there
	/// isn't a corresponding instance. For enumerable objects, [offset] and
	/// [count] allow retrieving a sub-range of properties.
	Future<Instance?> instanceFor(RemoteObject? remoteObject,
	{int? offset, int? count}) async {
	final primitive = _primitiveInstanceOrNull(remoteObject, offset, count);
	if (primitive != null) {
	return primitive;
	}
	final objectId = remoteObject?.objectId;
	if (remoteObject == null \|\| objectId == null) return null;

	// TODO: This is checking the JS object ID for the dart pattern we use for
	// VM objects, which seems wrong (and, we catch 'string' types above).
	if (isStringId(objectId)) {
	return _stringInstanceFor(remoteObject, offset, count);
	}

	final metaData = await ClassMetaData.metaDataFor(
	inspector.remoteDebugger, remoteObject, inspector);

	final classRef = metaData?.classRef;
	if (metaData == null \|\| classRef == null) return null;
	if (metaData.jsName == 'Function') {
	return _closureInstanceFor(remoteObject);
	}

	final properties = await debugger.getProperties(objectId,
	offset: offset, count: count, length: metaData.length);
	if (metaData.isSystemList) {
	return await _listInstanceFor(
	classRef, remoteObject, properties, offset, count);
	} else if (metaData.isSystemMap) {
	return await _mapInstanceFor(
	classRef, remoteObject, properties, offset, count);
	} else {
	return await _plainInstanceFor(classRef, remoteObject, properties);
	}
	}

	/// If [remoteObject] represents a primitive, return an [Instance] for it,
	/// otherwise return null.
	Instance? _primitiveInstanceOrNull(
	RemoteObject? remoteObject, int? offset, int? count) {
	switch (remoteObject?.type ?? 'undefined') {
	case 'string':
	return _stringInstanceFor(remoteObject, offset, count);
	case 'number':
	return _primitiveInstance(InstanceKind.kDouble, remoteObject);
	case 'boolean':
	return _primitiveInstance(InstanceKind.kBool, remoteObject);
	case 'undefined':
	return _primitiveInstance(InstanceKind.kNull, remoteObject);
	default:
	return null;
	}
	}

	/// Create a bound field for [property] in an instance of [classRef].
	Future<BoundField> _fieldFor(Property property, ClassRef classRef) async {
	final instance = await _instanceRefForRemote(property.value);
	return BoundField(
	decl: FieldRef(
	// TODO(grouma) - Convert JS name to Dart.
	name: property.name,
	declaredType: InstanceRef(
	kind: InstanceKind.kType,
	classRef: instance?.classRef,
	identityHashCode: createId().hashCode,
	id: createId()),
	owner: classRef,
	// TODO(grouma) - Fill these in.
	isConst: false,
	isFinal: false,
	isStatic: false,
	id: createId(),
	),
	value: instance);
	}

	/// Create a plain instance of [classRef] from [remoteObject] and the JS
	/// properties [properties].
	Future<Instance?> _plainInstanceFor(ClassRef classRef,
	RemoteObject remoteObject, List<Property> properties) async {
	final objectId = remoteObject.objectId;
	if (objectId == null) return null;
	final dartProperties = await _dartFieldsFor(properties, remoteObject);
	var boundFields = await Future.wait(
	dartProperties.map<Future<BoundField>>((p) => _fieldFor(p, classRef)));
	boundFields = boundFields
	.where((bv) => isDisplayableObject(bv.value))
	.toList()
	..sort(_compareBoundFields);
	final result = Instance(
	kind: InstanceKind.kPlainInstance,
	id: objectId,
	identityHashCode: remoteObject.objectId.hashCode,
	classRef: classRef)
	..fields = boundFields;
	return result;
	}

	int _compareBoundFields(BoundField a, BoundField b) {
	final aName = a.decl?.name;
	final bName = b.decl?.name;
	if (aName == null) return bName == null ? 0 : -1;
	if (bName == null) return 1;
	return aName.compareTo(bName);
	}

	/// The associations for a Dart Map or IdentityMap.
	Future<List<MapAssociation>> _mapAssociations(
	RemoteObject map, int? offset, int? count) async {
	// We do this in in awkward way because we want the keys and values, but we
	// can't return things by value or some Dart objects will come back as
	// values that we need to be RemoteObject, e.g. a List of int.
	final expression = '''
	function() {
	var sdkUtils = ${globalLoadStrategy.loadModuleSnippet}('dart_sdk').dart;
	var entries = sdkUtils.dloadRepl(this, "entries");
	entries = sdkUtils.dsendRepl(entries, "toList", []);
	function asKey(entry) {
	return sdkUtils.dloadRepl(entry, "key");
	}
	function asValue(entry) {
	return sdkUtils.dloadRepl(entry, "value");
	}
	return {
	keys: entries.map(asKey),
	values: entries.map(asValue)
	};
	}
	''';
	final keysAndValues = await inspector.jsCallFunctionOn(map, expression, []);
	final keys = await inspector.loadField(keysAndValues, 'keys');
	final values = await inspector.loadField(keysAndValues, 'values');
	final keysInstance = await instanceFor(keys, offset: offset, count: count);
	final valuesInstance =
	await instanceFor(values, offset: offset, count: count);
	final associations = <MapAssociation>[];
	final keyElements = keysInstance?.elements;
	final valueElements = valuesInstance?.elements;
	if (keyElements != null && valueElements != null) {
	Map.fromIterables(keyElements, valueElements).forEach((key, value) {
	associations.add(MapAssociation(key: key, value: value));
	});
	}
	return associations;
	}

	/// Create a Map instance with class [classRef] from [remoteObject].
	Future<Instance?> _mapInstanceFor(
	ClassRef classRef,
	RemoteObject remoteObject,
	List<Property> _,
	int? offset,
	int? count) async {
	final objectId = remoteObject.objectId;
	if (objectId == null) return null;
	// Maps are complicated, do an eval to get keys and values.
	final associations = await _mapAssociations(remoteObject, offset, count);
	final length = (offset == null && count == null)
	? associations.length
	: (await instanceRefFor(remoteObject))?.length;
	return Instance(
	identityHashCode: remoteObject.objectId.hashCode,
	kind: InstanceKind.kMap,
	id: objectId,
	classRef: classRef)
	..length = length
	..offset = offset
	..count = (associations.length == length) ? null : associations.length
	..associations = associations;
	}

	/// Create a List instance of [classRef] from [remoteObject] with the JS
	/// properties [properties].
	Future<Instance?> _listInstanceFor(
	ClassRef classRef,
	RemoteObject remoteObject,
	List<Property> properties,
	int? offset,
	int? count) async {
	final objectId = remoteObject.objectId;
	if (objectId == null) return null;

	/// TODO(annagrin): split into cases to make the logic clear.
	/// TODO(annagrin): make sure we use offset correctly.
	final numberOfProperties = _lengthOf(properties) ?? 0;
	final length = (offset == null && count == null)
	? numberOfProperties
	: (await instanceRefFor(remoteObject))?.length;
	final indexed = properties.sublist(
	0, min(count ?? length ?? numberOfProperties, numberOfProperties));
	final fields = await Future.wait(indexed
	.map((property) async => await _instanceRefForRemote(property.value)));
	return Instance(
	identityHashCode: remoteObject.objectId.hashCode,
	kind: InstanceKind.kList,
	id: objectId,
	classRef: classRef)
	..length = length
	..elements = fields
	..offset = offset
	..count = (numberOfProperties == length) ? null : numberOfProperties;
	}

	/// Return the value of the length attribute from [properties], if present.
	///
	/// This is only applicable to Lists or Maps, where we expect a length
	/// attribute. Even if a plain instance happens to have a length field, we
	/// don't use it to determine the properties to display.
	int? _lengthOf(List<Property> properties) {
	final lengthProperty = properties.firstWhere((p) => p.name == 'length');
	return lengthProperty.value?.value as int?;
	}

	/// Filter [allJsProperties] and return a list containing only those
	/// that correspond to Dart fields on [remoteObject].
	///
	/// This only applies to objects with named fields, not Lists or Maps.
	Future<List<Property>> _dartFieldsFor(
	List<Property> allJsProperties, RemoteObject remoteObject) async {
	// An expression to find the field names from the types, extract both
	// private (named by symbols) and public (named by strings) and return them
	// as a comma-separated single string, so we can return it by value and not
	// need to make multiple round trips.
	//
	// For maps and lists it's more complicated. Treat the actual SDK versions
	// of these as special.
	final fieldNameExpression = '''function() {
	const sdk = ${globalLoadStrategy.loadModuleSnippet}("dart_sdk");
	const sdk_utils = sdk.dart;
	const fields = sdk_utils.getFields(sdk_utils.getType(this)) \|\| [];
	if (!fields && (dart_sdk._interceptors.JSArray.is(this) \|\|
	dart_sdk._js_helper.InternalMap.is(this))) {
	// Trim off the 'length' property.
	const fields = allJsProperties.slice(0, allJsProperties.length -1);
	return fields.join(',');
	}
	const privateFields = sdk_utils.getOwnPropertySymbols(fields);
	const nonSymbolNames = privateFields
	.map(sym => sym.description
	.split('#').slice(-1)[0]);
	const publicFieldNames = sdk_utils.getOwnPropertyNames(fields);
	const symbolNames = Object.getOwnPropertySymbols(this)
	.map(sym => sym.description
	.split('#').slice(-1)[0]
	.split('.').slice(-1)[0]);
	return nonSymbolNames
	.concat(publicFieldNames)
	.concat(symbolNames).join(',');
	}
	''';
	final allNames = (await inspector
	.jsCallFunctionOn(remoteObject, fieldNameExpression, []))
	.value as String;
	final names = allNames.split(',');
	// TODO(#761): Better support for large collections.
	return allJsProperties
	.where((property) => names.contains(property.name))
	.toList();
	}

	/// Create an InstanceRef for an object, which may be a RemoteObject, or may
	/// be something returned by value from Chrome, e.g. number, boolean, or
	/// String.
	Future<InstanceRef?> instanceRefFor(Object value) {
	final remote = value is RemoteObject
	? value
	: RemoteObject({'value': value, 'type': _chromeType(value)});
	return _instanceRefForRemote(remote);
	}

	/// The Chrome type for a value.
	String? _chromeType(Object? value) {
	if (value == null) return null;
	if (value is String) return 'string';
	if (value is num) return 'number';
	if (value is bool) return 'boolean';
	if (value is Function) return 'function';
	return 'object';
	}

	/// Create an [InstanceRef] for the given Chrome [remoteObject].
	Future<InstanceRef?> _instanceRefForRemote(RemoteObject? remoteObject) async {
	// If we have a null result, treat it as a reference to null.
	if (remoteObject == null) {
	return kNullInstanceRef;
	}

	switch (remoteObject.type) {
	case 'string':
	final stringValue = remoteObject.value as String?;
	// TODO: Support truncation for long strings.
	// TODO(#777): dartIdFor() will return an ID containing the entire
	// string, even if we're truncating the string value here.
	return InstanceRef(
	identityHashCode: dartIdFor(remoteObject.value).hashCode,
	id: dartIdFor(remoteObject.value),
	classRef: classRefForString,
	kind: InstanceKind.kString)
	..valueAsString = stringValue
	..length = stringValue?.length;
	case 'number':
	return _primitiveInstanceRef(InstanceKind.kDouble, remoteObject);
	case 'boolean':
	return _primitiveInstanceRef(InstanceKind.kBool, remoteObject);
	case 'undefined':
	return _primitiveInstanceRef(InstanceKind.kNull, remoteObject);
	case 'object':
	final objectId = remoteObject.objectId;
	if (objectId == null) {
	return _primitiveInstanceRef(InstanceKind.kNull, remoteObject);
	}
	final metaData = await ClassMetaData.metaDataFor(
	inspector.remoteDebugger, remoteObject, inspector);
	if (metaData == null) return null;
	if (metaData.isSystemList) {
	return InstanceRef(
	kind: InstanceKind.kList,
	id: objectId,
	identityHashCode: remoteObject.objectId.hashCode,
	classRef: metaData.classRef)
	..length = metaData.length;
	}
	if (metaData.isSystemMap) {
	return InstanceRef(
	kind: InstanceKind.kMap,
	id: objectId,
	identityHashCode: remoteObject.objectId.hashCode,
	classRef: metaData.classRef)
	..length = metaData.length;
	}
	return InstanceRef(
	kind: InstanceKind.kPlainInstance,
	id: objectId,
	identityHashCode: remoteObject.objectId.hashCode,
	classRef: metaData.classRef);
	case 'function':
	final functionMetaData = await FunctionMetaData.metaDataFor(
	inspector.remoteDebugger, remoteObject);
	final objectId = remoteObject.objectId;
	if (objectId == null) {
	return _primitiveInstanceRef(InstanceKind.kNull, remoteObject);
	}
	return InstanceRef(
	kind: InstanceKind.kClosure,
	id: objectId,
	identityHashCode: remoteObject.objectId.hashCode,
	classRef: classRefForClosure)
	// TODO(grouma) - fill this in properly.
	..closureFunction = FuncRef(
	name: functionMetaData.name,
	id: createId(),
	// TODO(alanknight): The right ClassRef
	owner: classRefForUnknown,
	isConst: false,
	isStatic: false,
	// TODO(annagrin): get information about getters and setters from symbols.
	// https://github.com/dart-lang/sdk/issues/46723
	implicit: false)
	..closureContext = (ContextRef(length: 0, id: createId()));
	default:
	// Return null for an unsupported type. This is likely a JS construct.
	return null;
	}
	}
	}