Add logging to the incremental resolver.

pkg/analyzer/lib/src/generated/incremental_logger.dart

+// Copyright (c) 2014, 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 engine.incremental_logger;
+
+
+/**
+ * The shared instance of [Logger] used by several incremental resolution
+ * classes. It is initialized externally by the Analysis Engine client.
+ */
+Logger logger = new NullLogger();
+
+
+/**
+ * A simple hierarchical logger.
+ */
+abstract class Logger {
+  /**
+   * Mark an enter to a new section with the given [name].
+   */
+  void enter(String name);
+
+  /**
+   * Mark an exit from the current sections, logs the duration.
+   */
+  void exit();
+
+  /**
+   * Logs the given [obj].
+   */
+  void log(Object obj);
+}
+
+
+/**
+ * A [Logger] that does nothing.
+ */
+class NullLogger implements Logger {
+  @override
+  void enter(String name) {
+  }
+
+  @override
+  void exit() {
+  }
+
+  @override
+  void log(Object obj) {
+  }
+}
+
+
+/**
+ * A [Logger] that writes to a [StringSink].
+ */
+class StringSinkLogger implements Logger {
+  static const int _MAX_LINE_LENGTH = 512;
+  final StringSink _sink;
+  final List<_LoggerSection> _sectionStack = <_LoggerSection>[];
+  _LoggerSection _section = new _LoggerSection('', 'ROOT');
+
+  StringSinkLogger(this._sink);
+
+  @override
+  void enter(String name) {
+    log('+++ $name');
+    _sectionStack.add(_section);
+    _section = new _LoggerSection(_section.indent + '\t', name);
+  }
+
+  @override
+  void exit() {
+    DateTime now = new DateTime.now();
+    Duration duration = now.difference(_section.start);
+    String message = '--- ${_section.name} in ${duration.inMilliseconds} ms';
+    _section = _sectionStack.removeLast();
+    log(message);
+  }
+
+  @override
+  void log(Object obj) {
+    DateTime now = new DateTime.now();
+    String indent = _section.indent;
+    String objStr = _getObjectString(obj);
+    String line = '[$now] $indent$objStr';
+    _sink.writeln(line);
+  }
+
+  String _getObjectString(Object obj) {
+    if (obj == null) {
+      return 'null';
+    }
+    String str = obj.toString();
+    if (str.length < _MAX_LINE_LENGTH) {
+      return str;
+    }
+    return str.split('\n').map((String line) {
+      if (line.length > _MAX_LINE_LENGTH) {
+        line = line.substring(0, _MAX_LINE_LENGTH) + '...';
+      }
+      return line;
+    }).join('\n');
+  }
+}
+
+
+class _LoggerSection {
+  final DateTime start = new DateTime.now();
+  final String indent;
+  final String name;
+  _LoggerSection(this.indent, this.name);
+}