Support JSON output for pub build.

sdk/lib/_internal/pub/lib/src/utils.dart

Index: sdk/lib/_internal/pub/lib/src/utils.dart
diff --git a/sdk/lib/_internal/pub/lib/src/utils.dart b/sdk/lib/_internal/pub/lib/src/utils.dart
index c5f81c25c079486a05ce8f0b4b677305949587b8..6980cd5463de1b52b43f68cd884f5eabe8a274d6 100644
--- a/sdk/lib/_internal/pub/lib/src/utils.dart
+++ b/sdk/lib/_internal/pub/lib/src/utils.dart
@@ -855,7 +855,18 @@ class ApplicationException implements Exception {
 
 /// A class for command usage exceptions.
 class UsageException extends ApplicationException {
-  UsageException(String message)
+  /// The command usage information.
+  final String usage;
+
+  UsageException(String message, this.usage)
+      : super(message);
+
+  String toString() => "$message\n\n$usage";
+}
+
+/// A class for command input data exceptions.

[nweiz, 2014/03/05 02:36:52]

This description is pretty terse. I assume it refers to things like invalid
command-line arguments, but it would be nice to have some more description here.

[Bob Nystrom, 2014/03/07 00:42:18]

Reword a bit. It's basically an exception form of exit_codes.DATA.

[nweiz, 2014/03/07 00:57:13]

I still don't really understand how this should be used differently than
FormatError.

[Bob Nystrom, 2014/03/07 20:38:42]

I look at FormatException as "there's something wrong with the data you gave me,
so I'm bailing". dataError() means "I want pub to exit with exit_code.DATA now."

The fact that it throws an exception is an implementation detail. (And, in fact,
if we didn't have that annoying flush-before-exit stuff, it would just call
exit() and not throw anything.)

+class DataException extends ApplicationException {
+  DataException(String message)
       : super(message);
 }