Change --hide-package-warnings to --show-package-warnings and add hint on suppress warnings.

sdk/lib/_internal/compiler/implementation/source_file.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 source_file;
 
 import 'dart:math';
 import 'dart:convert' show UTF8;
 
 /**
@@ skipping 100 matching lines @@
 
   /**
    * Create a pretty string representation from a character position
    * in the file.
    */
   String getLocationMessage(String message, int start, int end,
                             bool includeText, String color(String x)) {
     var line = getLine(start);
     var column = getColumn(line, start);
 
-    var buf = new StringBuffer(
-        '${filename}:${line + 1}:${column + 1}: $message');
-    if (includeText) {
-      buf.write('\n');
+    var buf = new StringBuffer('${filename}:');
+    if (start != end || start != 0) {
+      // Line/column info is relevant.
+      buf.write('${line + 1}:${column + 1}:');
+    }
+    buf.write('\n$message\n');

[ahe, 2014/06/19 14:23:03]

Why did you add a newline before the message?

It ruins error parsing in Emacs as you cannot tell errors from info and
warnings.

[Johnni Winther, 2014/06/19 18:45:10]

Because on the command line the hint (at the beginning of the line) was easier
to find than the error message (after the file and position typically 60+
characters to the right) which was very confusing.

[ahe, 2014/06/19 18:58:03]

Makes sense. I'll add a comment.

How would feel about having an optional "kind" parameter which is added before
the first newline?

[Johnni Winther, 2014/06/19 20:08:48]

Sounds good.

+
+    if (start != end && includeText) {
       String textLine;
       // +1 for 0-indexing, +1 again to avoid the last line of the file
       if ((line + 2) < lineStarts.length) {
         textLine = slowSubstring(lineStarts[line], lineStarts[line+1]);
       } else {
         textLine = '${slowSubstring(lineStarts[line], length)}\n';
       }
 
       int toColumn = min(column + (end-start), textLine.length);
       buf.write(textLine.substring(0, column));
@@ skipping 50 matching lines @@
 
   int get length => text.length;
   set length(int v) { }
 
   String slowText() => text;
 
   List<int> slowUtf8Bytes() => UTF8.encode(text);
 
   String slowSubstring(int start, int end) => text.substring(start, end);
 }