Take Sam Elkhateeb's path for "path" dependencies and clean it up some.

utils/pub/validator/dependency.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 dependency_validator;
 
 import 'dart:async';
 
 import '../entrypoint.dart';
 import '../hosted_source.dart';
 import '../http.dart';
 import '../package.dart';
+import '../path_source.dart';
 import '../utils.dart';
 import '../validator.dart';
 import '../version.dart';
 
 /// A validator that validates a package's dependencies.
 class DependencyValidator extends Validator {
   DependencyValidator(Entrypoint entrypoint)
     : super(entrypoint);
 
   Future validate() {
@@ skipping 32 matching lines @@
       var primary = Version.primary(versions);
       if (primary != null) {
         constraint = _constraintForVersion(primary);
       } else {
         constraint = ref.constraint.toString();
         if (!ref.constraint.isAny && ref.constraint is! Version) {
           constraint = '"$constraint"';
         }
       }
 
-      warnings.add('Don\'t depend on "${ref.name}" from the ${ref.source.name} '
+      // Path sources are errors. Other sources are just warnings.
+      var messages = warnings;
+      if (ref.source is PathSource) {
+        messages = errors;
+      }
+
+      messages.add('Don\'t depend on "${ref.name}" from the ${ref.source.name} '
               'source. Use the hosted source instead. For example:\n'
           '\n'
           'dependencies:\n'
           '  ${ref.name}: $constraint\n'
           '\n'
           'Using the hosted source ensures that everyone can download your '
               'package\'s dependencies along with your package.');
     });
   }
 
@@ skipping 15 matching lines @@
   }
 
   /// Returns the suggested version constraint for a dependency that was tested
   /// against [version].
   String _constraintForVersion(Version version) {
     if (version.major != 0) return '">=$version <${version.major + 1}.0.0"';
     return '">=$version <${version.major}.${version.minor}.'
         '${version.patch + 1}"';
   }
 }