Support JSON output for pub build.

sdk/lib/_internal/pub/bin/pub.dart

 // Copyright (c) 2013, 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.
 
 import 'dart:async';
 import 'dart:io';
 
 import 'package:args/args.dart';
 import 'package:path/path.dart' as path;
 import 'package:stack_trace/stack_trace.dart';
@@ skipping 70 matching lines @@
 void runPub(String cacheDir, ArgResults options, List<String> arguments) {
   var captureStackChains =
       options['trace'] ||
       options['verbose'] ||
       options['verbosity'] == 'all';
 
   captureErrors(() => invokeCommand(cacheDir, options),
       captureStackChains: captureStackChains).catchError((error, Chain chain) {
     // This is basically the top-level exception handler so that we don't
     // spew a stack trace on our users.
-    var message;
+    var message = getErrorMessage(error);
+    log.error(message);
+    log.fine("Exception type: ${error.runtimeType}");
 
-    log.error(getErrorMessage(error));
-    log.fine("Exception type: ${error.runtimeType}");
+    if (log.json.enabled) {
+      if (error is UsageException) {
+        // Don't print usage info in JSON output.
+        log.json.error(error.message);
+      } else {
+        log.json.error(error);
+      }
+    }
 
     if (options['trace'] || !isUserFacingException(error)) {
       log.error(chain.terse);
     } else {
       log.fine(chain.terse);
     }
 
     if (error is ApplicationException && error.innerError != null) {
       var message = "Wrapped exception: ${error.innerError}";
       if (error.innerTrace != null) message = "$message\n${error.innerTrace}";
@@ skipping 19 matching lines @@
     return flushThenExit(exit_codes.SUCCESS);
   });
 }
 
 /// Returns the appropriate exit code for [exception], falling back on 1 if no
 /// appropriate exit code could be found.
 int chooseExitCode(exception) {
   if (exception is HttpException || exception is HttpException ||
       exception is SocketException || exception is PubHttpException) {
     return exit_codes.UNAVAILABLE;
-  } else if (exception is FormatException) {
+  } else if (exception is FormatException || exception is DataException) {
     return exit_codes.DATA;
   } else if (exception is UsageException) {
     return exit_codes.USAGE;
   } else {
     return 1;
   }
 }
 
 /// Walks the command tree and runs the selected pub command.
 Future invokeCommand(String cacheDir, ArgResults mainOptions) {
@@ skipping 55 matching lines @@
     if (Platform.operatingSystem != 'windows') return null;
 
     return runProcess('ver', []).then((result) {
       if (result.stdout.join('\n').contains('XP')) {
         log.error('Sorry, but pub is not supported on Windows XP.');
         return flushThenExit(exit_codes.USAGE);
       }
     });
   });
 }