Fix log output logic to not overwrite the last line of a multi-line log (#305)

Author: kevmoo

build_runner/lib/src/generate/options.dart

@@ -2,6 +2,7 @@
 // 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:convert';
 import 'dart:io';
 
 import 'package:build/build.dart';
@@ -105,12 +106,16 @@ void _defaultLogListener(LogRecord record) {
     }
   }
 
-  if (record.level > Level.INFO || !_isPosixTerminal) {
+  var message = lines.join('\n');
+
+  var multiLine = LineSplitter.split(message).length > 1;
+
+  if (record.level > Level.INFO || !_isPosixTerminal || multiLine) {
+    // Add an extra line to the output so the last line is written over.
     lines.add('');
+    message = lines.join('\n');
   }
 
-  var message = lines.join('\n');
-
   if (record.level >= Level.SEVERE) {
     stderr.write(message);
   } else {

build_runner/pubspec.yaml

@@ -1,5 +1,5 @@
 name: build_runner
-version: 0.3.4
+version: 0.3.5-dev
 description: Tools to write binaries that run builders.
 author: Dart Team <[email protected]>
 homepage: https://github.com/dart-lang/build