Improve barback/pub logging.

sdk/lib/_internal/pub/lib/src/barback/pub_barback_logger.dart

Index: sdk/lib/_internal/pub/lib/src/barback/pub_barback_logger.dart
diff --git a/sdk/lib/_internal/pub/lib/src/barback/pub_barback_logger.dart b/sdk/lib/_internal/pub/lib/src/barback/pub_barback_logger.dart
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index 0000000000000000000000000000000000000000..374e1581d0e3790885ceb9b11975b028f7e8d7a9
--- /dev/null
+++ b/sdk/lib/_internal/pub/lib/src/barback/pub_barback_logger.dart
@@ -0,0 +1,63 @@
+// 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.
+
+library pub.pub_barback_logger;
+
+import 'package:barback/barback.dart';
+
+import '../log.dart' as log;
+
+/// A [BarbackLogger] that routes through pub's logging code.
+class PubBarbackLogger implements BarbackLogger {
+  /// Since both [LogEntry] objects and the message itself often redundantly
+  /// show the same context like the file where an error occurred, this tries
+  /// to avoid showing redundant data in the entry.
+  void logEntry(LogEntry entry) {
+    messageMentions(String text) {
+      return entry.message.toLowerCase().contains(text.toLowerCase());
+    }
+
+    var prefixParts = [];
+
+    // Show the level (unless the message mentions it.)

[nweiz, 2013/10/16 19:41:27]

".)" -> ")."

[Bob Nystrom, 2013/10/28 23:45:56]

Done.

+    if (!messageMentions(entry.level.name)) {
+      prefixParts.add("${entry.level} in");
+    }
+
+    // Show the transformer.
+    prefixParts.add(entry.transform.transformer);
+
+    // Mention the primary input of the transform unless the message seems to.
+    if (!messageMentions(entry.transform.primaryId.path)) {
+      prefixParts.add("on ${entry.transform.primaryId}");
+    }
+
+    // If the relevant asset isn't the primary input, mention it unless the
+    // message already does.
+    if (entry.asset != entry.transform.primaryId &&
+        !messageMentions(entry.asset.path)) {
+      prefixParts.add("with input ${entry.asset}");
+    }
+
+    var prefix = "[${prefixParts.join(' ')}]:";

[nweiz, 2013/10/16 19:41:27]

Minor formatting thing, but it seems weird to have a colon after this prefix.

[Bob Nystrom, 2013/10/28 23:45:56]

I think it helps make it clearer that the prefix is associated with the
following line and not the previous:

...
[SomeTransformer path/to/asset.txt]
This is an error message.
[SomeTransformer path/to/asset.txt]
This is an error message.
[SomeTransformer path/to/foo.txt]
This is an error message. <-- wait, is this for foo or bar?
[SomeTransformer path/to/bar.txt]
This is an error message.
[SomeTransformer path/to/asset.txt]
...

+    var message = entry.message;
+    if (entry.span != null) {
+      message = entry.span.getLocationMessage(entry.message);
+    }
+
+    switch (entry.level) {
+      case LogLevel.ERROR:
+        log.error("${log.red(prefix)}\n$message");

[nweiz, 2013/10/16 19:41:27]

Use prefixLines to make it clear that the message belongs to the given log
entry.

[Bob Nystrom, 2013/10/28 23:45:56]

See above. In my manual testing, I thought this form looked pretty nice. The
prefix is too long to put any part of the message on the same line as it. Given
that, it seemed like a waste of space to prefix every line.

[nweiz, 2013/10/29 00:40:13]

I just meant prefixing it with a couple of spaces, not the entire location
string. So it ends up looking like

[WARNING in transformer on file]
  text of warning
  more text

+        break;
+
+      case LogLevel.WARNING:
+        log.warning("${log.yellow(prefix)}\n$message");
+        break;
+
+      case LogLevel.INFO:
+        log.message("$prefix\n$message");
+        break;
+    }
+  }
+}