Start implementing IncrementalClassHierarchy.

pkg/kernel/lib/src/incremental_class_hierarchy.dart

+// Copyright (c) 2017, 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.
+library kernel.incremental_class_hierarchy;
+
+import 'dart:math';
+
+import 'package:kernel/ast.dart';
+import 'package:kernel/class_hierarchy.dart';
+
+/// Lazy and incremental implementation of [ClassHierarchy].
+class IncrementalClassHierarchy implements ClassHierarchy {
+  /// The mapping from [Class]es to the corresponding [_ClassInfo]s.
+  /// It is filled lazily as the client requests information about classes.
+  final Map<Class, _ClassInfo> _info = {};
+
+  @override
+  Iterable<Class> get classes {
+    // TODO: implement classes

[Paul Berry, 2017/06/01 21:39:03]

Change the TODOs in this file to "TODO(scheglov)"

[scheglov, 2017/06/01 21:50:35]

Done.

+    return null;

[Paul Berry, 2017/06/01 21:39:03]

I'd recommend replacing this line (and the other "return null;" lines) with
"throw new UnimplementedError();".  Less likely to result in confusing failures.

[scheglov, 2017/06/01 21:50:35]

Done.

+  }
+
+  @override
+  Class get rootClass {
+    // TODO: implement rootClass
+    return null;
+  }
+
+  @override
+  void forEachOverridePair(Class class_,
+      callback(Member declaredMember, Member interfaceMember, bool isSetter)) {
+    // TODO: implement forEachOverridePair
+    throw new UnimplementedError();
+  }
+
+  @override
+  Supertype getClassAsInstanceOf(Class class_, Class superclass) {
+    // TODO: implement getClassAsInstanceOf
+    throw new UnimplementedError();
+  }
+
+  @override
+  int getClassDepth(Class node) {
+    var info = _getInfo(node);
+    if (info.depth < 0) {
+      int superDepth = -1;
+      if (node.supertype != null) {
+        superDepth = max(superDepth, getClassDepth(node.supertype.classNode));
+      }
+      if (node.mixedInType != null) {
+        superDepth = max(superDepth, getClassDepth(node.mixedInType.classNode));
+      }
+      for (var supertype in node.implementedTypes) {
+        superDepth = max(superDepth, getClassDepth(supertype.classNode));
+      }
+      info.depth = superDepth + 1;
+    }
+
+    return info.depth;
+  }
+
+  @override
+  InterfaceType getClassicLeastUpperBound(
+      InterfaceType type1, InterfaceType type2) {
+    // TODO: implement getClassicLeastUpperBound
+    throw new UnimplementedError();
+  }
+
+  @override
+  int getClassIndex(Class class_) {
+    // TODO: implement getClassIndex
+    throw new UnimplementedError();
+  }
+
+  @override
+  Member getDispatchTarget(Class class_, Name name, {bool setter: false}) {
+    // TODO: implement getDispatchTarget
+    throw new UnimplementedError();
+  }
+
+  @override
+  Member getInterfaceMember(Class class_, Name name, {bool setter: false}) {
+    // TODO: implement getInterfaceMember
+    throw new UnimplementedError();
+  }
+
+  @override
+  List<Class> getRankedSuperclasses(Class class_) {
+    // TODO: implement getRankedSuperclasses
+    throw new UnimplementedError();
+  }
+
+  @override
+  InterfaceType getTypeAsInstanceOf(InterfaceType type, Class superclass) {
+    // TODO: implement getTypeAsInstanceOf
+    throw new UnimplementedError();
+  }
+
+  @override
+  bool hasProperSubtypes(Class class_) {
+    // TODO: implement hasProperSubtypes
+    throw new UnimplementedError();
+  }
+
+  /// Return the [_ClassInfo] for the [node].
+  _ClassInfo _getInfo(Class node) {
+    var info = _info[node];

[Paul Berry, 2017/06/01 21:39:03]

I think a more performant implementation of this function would be:

_ClassInfo _getInfo(Class node) =>
    _info.putIfAbsent(node, () => new _ClassInfo(node));

(on a miss, it requires just one hashtable lookup rather than two).

[scheglov, 2017/06/01 21:50:35]

Done.

+    if (info == null) {
+      info = new _ClassInfo(node);
+      _info[node] = info;
+    }
+    return info;
+  }
+}
+
+/// Information about a [Class].
+class _ClassInfo {
+  final Class node;
+
+  /// The number of steps in the longest inheritance path from the class
+  /// to [Object].

[Paul Berry, 2017/06/01 21:39:03]

", or -1 if the depth has not been computed yet."

[scheglov, 2017/06/01 21:50:35]

Done.

+  int depth = -1;
+
+  _ClassInfo(this.node);
+}