Add a library for manipulating stack traces.

pkg/stack_trace/lib/src/trace.dart

+// Copyright (c) 2013, 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 trace;
+
+import 'dart:uri';
+
+import 'frame.dart';
+
+/// A stack trace, comprised of a list of stack frames.
+class Trace implements StackTrace {
+  // TODO(nweiz): make this read-only once issue 8321 is fixed.
+  /// The stack frames that comprise this stack trace.
+  final List<Frame> frames;
+
+  /// Returns a human-readable representation of [stackTrace]. If [terse] is
+  /// set, this folds together multiple stack frames from the Dart core
+  /// libraries, so that only the core library method directly called from user
+  /// code is visible (see [Trace.terse]).
+  static String format(StackTrace stackTrace, {bool terse: true}) {
+    var trace = new Trace.from(stackTrace);
+    if (terse) trace = trace.terse;
+    return trace.toString();
+  }
+
+  /// Returns the current stack trace.
+  ///
+  /// By default, the first frame of this trace will be the line where
+  /// [Trace.current] is called. If [level] is passed, the trace will start that
+  /// many frames up instead.
+  factory Trace.current([int level=0]) {
+    if (level < 0) {
+      throw new ArgumentError("Argument [level] must be greater than or equal "
+          "to 0.");
+    }
+
+    try {
+      throw '';
+    } catch (_, nativeTrace) {
+      var trace = new Trace.from(nativeTrace);
+      return new Trace(trace.frames.skip(level + 1));
+    }
+  }
+
+  /// Returns a new stack trace containing the same data as [trace].
+  ///
+  /// If [trace] is a native [StackTrace], its data will be parsed out; if it's
+  /// a [Trace], it will be returned as-is.
+  factory Trace.from(StackTrace trace) {
+    if (trace is Trace) return trace;
+    return new Trace.parse(trace.fullStackTrace);
+  }
+
+  /// Parses a string representation of a stack trace.
+  ///
+  /// [trace] should be formatted in the same way as native stack traces.
+  Trace.parse(String trace)
+      : this(trace.trim().split("\n").map((line) => new Frame.parse(line)));
+
+  /// Returns a new [Trace] comprised of [frames].
+  Trace(Iterable<Frame> frames)
+      : frames = frames.toList();
+
+  // TODO(nweiz): Keep track of which [Frame]s are part of the partial stack
+  // trace and only print them.
+  /// Returns a string representation of this stack trace.
+  ///
+  /// This is identical to [toString]. It will not be formatted in the manner of
+  /// native stack traces.
+  String get stackTrace => toString();
+
+  /// Returns a string representation of this stack trace.
+  ///
+  /// This is identical to [toString]. It will not be formatted in the manner of
+  /// native stack traces.
+  String get fullStackTrace => toString();
+
+  /// Returns a terser version of [this]. This is accomplished by folding
+  /// together multiple stack frames from the core library. If multiple such
+  /// frames appear in a row, only the last (the one directly called by user
+  /// code) is kept. Core library patches are also renamed to remove their
+  /// `-patch` suffix.
+  Trace get terse {
+    return new Trace(frames.reversed.reduce(<Frame>[], (newFrames, frame) {
+      if (!frame.isCore) {
+        newFrames.add(frame);

[Bob Nystrom, 2013/03/27 00:46:44]

Given that you are imperatively building up a result list here, using reduce()
seems a bit perverse. How about just using a for loop?

[nweiz, 2013/03/27 21:15:46]

Done.

+      } else if (newFrames.isEmpty || !newFrames.last.isCore) {
+        var library = frame.library.replaceAll(new RegExp(r"-patch$"), '');

[Bob Nystrom, 2013/03/27 00:46:44]

Hoist this regex out to a top level final variable?

[nweiz, 2013/03/27 21:15:46]

I really hate that we have to do this for every regular expression that we use,
but done.

+        newFrames.add(new Frame(
+            Uri.parse(library), frame.line, frame.column, frame.member));
+      }
+
+      return newFrames;
+    }).reversed);
+  }
+
+  /// Returns a human-readable string representation of [this].
+  String toString() {
+    if (frames.length == '') return '';
+
+    // Figure out the longest path so we know how much to pad.
+    var longest = frames.map((frame) => frame.location.length).max();
+
+    // Print out the stack trace nicely formatted.
+    return frames.map((frame) {
+      return '${_padRight(frame.location, longest)}  ${frame.member}\n';
+    }).join();
+  }
+
+  /// Returns [string] with enough spaces added to the end to make it [length]
+  /// characters long.
+  String _padRight(String string, int length) {

[Bob Nystrom, 2013/03/27 00:46:44]

Make a top-level function? It doesn't access any instance state.

[nweiz, 2013/03/27 21:15:46]

Done.

+    if (string.length >= length) return string;
+
+    var result = new StringBuffer();
+    result.write(string);
+    for (var i = 0; i < length - string.length; i++) {
+      result.write(' ');
+    }
+
+    return result.toString();
+  }
+}