Add option to automatically record stack trace in logging (fixes #2)

lib/logging.dart

 // Copyright (c) 2012, 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 logging;
 
 import 'dart:async';
 import 'dart:collection';
 
 /**
  * Whether to allow fine-grain logging and configuration of loggers in a
  * hierarchy. When false, all logging is merged in the root logger.
  */
 bool hierarchicalLoggingEnabled = false;
 
 /**
+ * Automatically record stack traces for any message of this level or above.
+ * Because this is expensive, this is off by default.
+ */
+Level recordStackTraceAtLevel = Level.OFF;
+
+/**
  * Level for the root-logger. This will be the level of all loggers if
  * [hierarchicalLoggingEnabled] is false.
  */
 Level _rootLevel = Level.INFO;
 
 /**
  * Use a [Logger] to log debug messages. [Logger]s are named using a
  * hierarchical dot-separated name convention.
  */
 class Logger {
@@ skipping 111 matching lines @@
    *
    * The log record will contain a field for the zone in which this call was
    * made.
    * This can be advantagous if a log listener wants to handle records of
    * different zones differently (e.g. group log records by http-request if each
    * http-request handler runs in it's own zone).
    */
   void log(Level logLevel, message,
       [Object error, StackTrace stackTrace, Zone zone]) {
     if (isLoggable(logLevel)) {
-      // If message is a Function, evaluate it.
       if (message is Function) message = message();
-      // If message is still not a String, call toString().
       if (message is! String) message = message.toString();
-      // Only record the current zone if it was not given.
+      if (stackTrace == null && logLevel >= recordStackTraceAtLevel) {
+        try {
+          throw "log stack trace";

[Jennifer Messerly, 2015/05/07 22:32:19]

include message here? e.g.

    throw "log ${logLevel.name} $message"

that might make it more understandable in some tools?

[Siggi Cherem (dart-lang), 2015/05/08 00:31:03]

Good point. Done.

+        } catch (e, t) {
+          stackTrace = t;
+        }
+      }
       if (zone == null) zone = Zone.current;
 
       var record =
           new LogRecord(logLevel, message, fullName, error, stackTrace, zone);
 
       if (hierarchicalLoggingEnabled) {
         var target = this;
         while (target != null) {
           target._publish(record);
           target = target.parent;
@@ skipping 167 matching lines @@
   /** Zone of the calling code which resulted in this LogRecord. */
   final Zone zone;
 
   LogRecord(this.level, this.message, this.loggerName,
       [this.error, this.stackTrace, this.zone])
       : time = new DateTime.now(),
         sequenceNumber = LogRecord._nextNumber++;
 
   String toString() => '[${level.name}] $loggerName: $message';
 }