Support JSON output for pub build.

sdk/lib/_internal/pub/lib/src/log.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.
 
 /// Message logging.
 library pub.log;
 
 import 'dart:async';
+import 'dart:convert';
 import 'dart:io';
 
 import 'package:path/path.dart' as p;
 
 import 'io.dart';
 import 'transcript.dart';
 import 'utils.dart';
 
 typedef LogFn(Entry entry);
 final Map<Level, LogFn> _loggers = new Map<Level, LogFn>();
@@ skipping 183 matching lines @@
 void recordTranscript() {
   _transcript = new Transcript<Entry>(_MAX_TRANSCRIPT);
 }
 
 /// If [recordTranscript()] was called, then prints the previously recorded log
 /// transcript to stderr.
 void dumpTranscript() {
   if (_transcript == null) return;
 
   stderr.writeln('---- Log transcript ----');
-  _transcript.forEach(_logToStderrWithLabel, (discarded) {
+  _transcript.forEach((entry) {
+    _printToStream(stderr, entry, showLabel: true);

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

If you're keeping _logToStderrWithLabel, I don't understand this change. If
you're getting rid of it, you should delete it below.

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

Calling _printToStream() directly skips the if (json.enabled) check in
_logToStream. If the transcript gets dumped on a failure, we want to always dump
it, even in JSON mode.

+  }, (discarded) {
     stderr.writeln('---- ($discarded discarded) ----');
   });
   stderr.writeln('---- End log transcript ----');
 }
 
 /// Prints [message] then slowly prints additional "..." after it until the
 /// future returned by [callback] completes. If anything else is logged during
 /// this, it cancels the progress.
 Future progress(String message, Future callback()) {
+  if (json.enabled) return callback();
+
   if (_progressTimer != null) throw new StateError("Already in progress.");
 
   _progressMessage = '$message...';
   stdout.write(_progressMessage);
 
   _progressTimer = new Timer.periodic(new Duration(milliseconds: 500), (_) {
     stdout.write('.');
     _progressMessage += '.';
   });
 
@@ skipping 117 matching lines @@
 void _logToStderr(Entry entry) {
   _logToStream(stderr, entry, showLabel: false);
 }
 
 /// Log function that prints the message to stderr with the level name.
 void _logToStderrWithLabel(Entry entry) {
   _logToStream(stderr, entry, showLabel: true);
 }
 
 void _logToStream(IOSink sink, Entry entry, {bool showLabel}) {
+  if (json.enabled) return;
+
+  _printToStream(sink, entry, showLabel: showLabel);
+}
+
+void _printToStream(IOSink sink, Entry entry, {bool showLabel}) {
   _stopProgress();
 
   bool firstLine = true;
   for (var line in entry.lines) {
     if (showLabel) {
       if (firstLine) {
         sink.write('${entry.level.name}: ');
       } else {
         sink.write('    | ');
       }
     }
 
     sink.writeln(line);
 
     firstLine = false;
   }
 }
+
+/// Namespace-like class for collecting the methods for JSON logging.
+class _JsonLogger {
+  /// Whether logging should use machine-friendl JSON output or human-friendly

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

"friendl" -> "friendly"

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

Done.

+  /// text.
+  ///
+  /// If set to `true`, then all regular logging is not printed. Logged

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

"no regular logging is printed"

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

Done.

+  /// messages will still be recorded and displayed if the transcript is
+  /// printed.
+  bool enabled = false;
+
+  /// Creates an error JSON object for [error] and prints it if JSON output
+  /// is enabled.

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

Mention that this prints to stdout as opposed to stderr.

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

Done.

+  void error(error) {

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

This should take an optional StackTrace as well.

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

Done.

+    var errorJson = {"error": error.toString()};
+
+    var trace;
+    if (error is Error) trace = error.stackTrace;
+    if (trace != null) {
+      errorJson["stackTrace"] = trace;

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

We should [new Chain.forTrace] this.

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

Done.

+    }
+
+    this.message(errorJson);
+  }
+
+  /// Encodes [message] to JSON and prints it if JSON output is enabled.
+  void message(message) {
+    if (!enabled) return;
+
+    // TODO(rnystrom): Should errors be printed to stderr?

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

I think stdout is fine. Since the errors have identifying metadata anyway,
printing some to stderr and some to stdout just complicates things.

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

Done.

+    print(JSON.encode(message));
+  }
+}
+
+/// The singleton instance so that we can have a nice api like:
+///
+///     log.json.error(...);
+final json = new _JsonLogger();

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

Nit: I'd expect this to be at the top of the file, like other library variables.

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

Done.