Printing a useful error message if a version field is a num

sdk/lib/_internal/pub/lib/src/pubspec.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.
 
 library pub.pubspec;
 
 import 'package:path/path.dart' as path;
 import 'package:pub_semver/pub_semver.dart';
 import 'package:source_span/source_span.dart';
 import 'package:yaml/yaml.dart';
@@ skipping 56 matching lines @@
   Version get version {
     if (_version != null) return _version;
 
     var version = fields['version'];
     if (version == null) {
       _version = Version.none;
       return _version;
     }
 
     var span = fields.nodes['version'].span;
+    if (version is num) {
+      _error('"version" field must be written in MAJOR.MINOR.PATCH[SUFFIX] format', span);

[Bob Nystrom, 2014/10/06 16:19:34]

I think the all caps part might confuse users a bit. How about:

"version" field must have three numeric components: major, minor, and patch.
Instead of "$version", consider "$fixed".

where fixed is the original version with ".0.0" added if it's an int or ".0"
added if it is a float.

Also, long line.

[srawlins, 2014/10/06 17:33:08]

Love it! Done.

+    }
     if (version is! String) {
       _error('"version" field must be a string.', span);
     }
 
     _version = _wrapFormatException('version number', span,
         () => new Version.parse(version));
     return _version;
   }
   Version _version;
 
@@ skipping 492 matching lines @@
     implements ApplicationException {
   PubspecException(String message, SourceSpan span)
       : super(message, span);
 }
 
 /// Returns whether [uri] is a file URI.
 ///
 /// This is slightly more complicated than just checking if the scheme is
 /// 'file', since relative URIs also refer to the filesystem on the VM.
 bool _isFileUri(Uri uri) => uri.scheme == 'file' || uri.scheme == '';