Migrate pub away from throwing strings.

utils/pub/pub.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.
 
 /// The main entrypoint for the pub command line application.
 library pub;
 
 import 'dart:async';
 import 'dart:io';
 import 'dart:math';
@@ skipping 241 matching lines @@
         // base Exception type so there's no easy way to know if it's available
         // short of a giant pile of type tests for each known exception type.
         //
         // So just try it. If it throws, default to toString().
         message = error.message;
       } on NoSuchMethodError catch (_) {
         message = error.toString();
       }
 
       log.error(message);
-      if (globalOptions['trace'] && trace != null) {
-        log.error(trace);
+
+      if (trace != null) {
+        if (globalOptions['trace'] || !isUserFacingException(error)) {
+          log.error(trace);
+        } else {
+          log.fine(trace);
+        }
+      }
+
+      if (globalOptions['trace']) {
         log.dumpTranscript();
-      } else {
-        log.fine(trace);
+      } else if (!isUserFacingException(error)) {
+        log.error("""
+This is an unexpected error. Please run
+
+    pub --trace ${new Options().arguments.map((arg) => "'$arg'").join(' ')}
+
+and include the results in a bug report on http://dartbug.com/new.
+""");
       }
 
       exit(_chooseExitCode(error));
     }
 
     new Future.sync(() {
       if (requiresEntrypoint) {
         // TODO(rnystrom): Will eventually need better logic to walk up
         // subdirectories until we hit one that looks package-like. For now,
         // just assume the cwd is it.
@@ skipping 48 matching lines @@
     if (exception is HttpException || exception is HttpParserException ||
         exception is SocketIOException || exception is PubHttpException) {
       return exit_codes.UNAVAILABLE;
     } else if (exception is FormatException) {
       return exit_codes.DATA;
     } else {
       return 1;
     }
   }
 }