Allow application of external mixins to generated dart protos.

lib/message_generator.dart

 // 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.
 
 part of protoc;
 
 class MessageGenerator extends ProtobufContainer {
-  // Returns the mixin for this message, or null if none.
-  static PbMixin _getMixin(DescriptorProto desc, PbMixin defaultValue) {
-    if (!desc.hasOptions()) return defaultValue;
-    if (!desc.options.hasExtension(Dart_options.mixin)) return defaultValue;
+  /// Returns the mixin for this message, or null if none.
+  ///
+  /// First searches [declaredMixins], then internal mixins declared by
+  /// [findMixin].
+  static PbMixin _getMixin(DescriptorProto desc,
+      Map<String, DartMixin> declaredMixins, String defaultMixin) {
+    PbMixin resolveMixin(String name, {List<String> children: const []}) {
+      if (name.isEmpty) return null; // don't use a mixin (override any default)
+
+      if (declaredMixins.containsKey(name)) {
+        var dartMixin = declaredMixins[name];
+
+        PbMixin parent;
+        if (dartMixin.hasParent()) {
+          var parentName = dartMixin.parent;
+          if (children.contains(parentName)) {

[skybrian, 2016/06/22 20:29:52]

Seems better to check for cycles sooner? The error is not in the Message that
references the mixin; it is in the "mixins" file option.

(The cycle is still there even if no message references the mixin, so it should
probably still be an error.)

[frederikmutzel, 2016/06/23 12:30:16]

Moved to file_generator.

I also moved the conversion to PbMixin and made sure that the generated PbMixins
are unique (otherwise you could get double imports).

+            var chain = children.join('->') + '->$name';
+            throw ('cycle in mixin parents: $chain');
+          }
+          children.add(name);
+          var parent = resolveMixin(dartMixin.parent, children: children);
+          if (parent == null) {
+            throw ('unknown mixin parent: $parent of $name');
+          }
+        }
+        return new PbMixin(dartMixin.name,
+            importFrom: dartMixin.importFrom, parent: parent);
+      }
+
+      var internalMixin = findMixin(name);
+      if (internalMixin == null) throw ("unknown mixin class: ${name}");
+      return internalMixin;
+    }
+
+    if (!desc.hasOptions() || !desc.options.hasExtension(Dart_options.mixin)) {
+      return resolveMixin(defaultMixin);
+    }
 
     String name = desc.options.getExtension(Dart_options.mixin);
-    if (name.isEmpty) return null; // don't use a mixin (override any default)
-    var mixin = findMixin(name);
-    if (mixin == null) {
-      throw ("unknown mixin class: ${name}");
-    }
-    return mixin;
+    return resolveMixin(name);
   }
 
   final String classname;
   final String fqname;
   final PbMixin mixin;
 
   final ProtobufContainer _parent;
   final DescriptorProto _descriptor;
   final List<EnumGenerator> _enumGenerators = <EnumGenerator>[];
   final List<MessageGenerator> _messageGenerators = <MessageGenerator>[];
   final List<ExtensionGenerator> _extensionGenerators = <ExtensionGenerator>[];
 
   // populated by resolve()
   List<ProtobufField> _fieldList;
 
   MessageGenerator(DescriptorProto descriptor, ProtobufContainer parent,
-      PbMixin defaultMixin)
+      Map<String, DartMixin> declaredMixins, String defaultMixin)
       : _descriptor = descriptor,
         _parent = parent,
         classname = (parent.classname == '')
             ? descriptor.name
             : '${parent.classname}_${descriptor.name}',
         fqname = (parent == null || parent.fqname == null)
             ? descriptor.name
             : (parent.fqname == '.'
                 ? '.${descriptor.name}'
                 : '${parent.fqname}.${descriptor.name}'),
-        mixin = _getMixin(descriptor, defaultMixin) {
+        mixin = _getMixin(descriptor, declaredMixins, defaultMixin ?? '') {
     for (EnumDescriptorProto e in _descriptor.enumType) {
       _enumGenerators.add(new EnumGenerator(e, this));
     }
 
     for (DescriptorProto n in _descriptor.nestedType) {
-      _messageGenerators.add(new MessageGenerator(n, this, defaultMixin));
+      _messageGenerators
+          .add(new MessageGenerator(n, this, declaredMixins, defaultMixin));
     }
 
     for (FieldDescriptorProto x in _descriptor.extension) {
       _extensionGenerators.add(new ExtensionGenerator(x, this));
     }
   }
 
   String get package => _parent.package;
 
   /// The generator of the .pb.dart file that will declare this type.
@@ skipping 310 matching lines @@
 
     for (var m in _messageGenerators) {
       m.generateConstants(out);
     }
 
     for (var e in _enumGenerators) {
       e.generateConstants(out);
     }
   }
 }