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

sdk/lib/_internal/compiler/implementation/source_file.dart

Index: sdk/lib/_internal/compiler/implementation/source_file.dart
diff --git a/sdk/lib/_internal/compiler/implementation/source_file.dart b/sdk/lib/_internal/compiler/implementation/source_file.dart
index 45636ea7b13360f0a786a358f9e6234a5c2c92bc..af1a2be15d336bf34c0262f46ecfb67198468a62 100644
--- a/sdk/lib/_internal/compiler/implementation/source_file.dart
+++ b/sdk/lib/_internal/compiler/implementation/source_file.dart
@@ -118,10 +118,14 @@ abstract class SourceFile {
     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) {