Allow application of external mixins to generated dart protos.

lib/message_generator.dart

Index: lib/message_generator.dart
diff --git a/lib/message_generator.dart b/lib/message_generator.dart
index 4dd64bba2066d855bef896a69e4a1f39d2dc033c..4a07bba78d36072aa97bfd8a9efba1605de5e2db 100644
--- a/lib/message_generator.dart
+++ b/lib/message_generator.dart
@@ -5,18 +5,46 @@
 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);
+      }
 
-    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}");
+      var internalMixin = findMixin(name);
+      if (internalMixin == null) throw ("unknown mixin class: ${name}");
+      return internalMixin;
     }
-    return mixin;
+
+    if (!desc.hasOptions() || !desc.options.hasExtension(Dart_options.mixin)) {
+      return resolveMixin(defaultMixin);
+    }
+
+    String name = desc.options.getExtension(Dart_options.mixin);
+    return resolveMixin(name);
   }
 
   final String classname;
@@ -33,7 +61,7 @@ class MessageGenerator extends ProtobufContainer {
   List<ProtobufField> _fieldList;
 
   MessageGenerator(DescriptorProto descriptor, ProtobufContainer parent,
-      PbMixin defaultMixin)
+      Map<String, DartMixin> declaredMixins, String defaultMixin)
       : _descriptor = descriptor,
         _parent = parent,
         classname = (parent.classname == '')
@@ -44,13 +72,14 @@ class MessageGenerator extends ProtobufContainer {
             : (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) {