fix: Support proto2 extension groups

src/object.js

@@ -232,23 +232,21 @@ ReflectionObject.prototype._resolveFeatures = function _resolveFeatures(edition)
             throw new Error("Unknown edition: " + edition);
         }
         this._features = Object.assign(defaults, protoFeatures || {});
-        this._featuresResolved = true;
-        return;
-    }
-
-    // fields in Oneofs aren't actually children of them, so we have to
-    // special-case it
-    /* istanbul ignore else */
-    if (this.partOf instanceof OneOf) {
-        var lexicalParentFeaturesCopy = Object.assign({}, this.partOf._features);
-        this._features = Object.assign(lexicalParentFeaturesCopy, protoFeatures || {});
-    } else if (this.declaringField) {
-        // Skip feature resolution of sister fields.
-    } else if (this.parent) {
-        var parentFeaturesCopy = Object.assign({}, this.parent._features);
-        this._features = Object.assign(parentFeaturesCopy, protoFeatures || {});
     } else {
-        throw new Error("Unable to find a parent for " + this.fullName);
+        // fields in Oneofs aren't actually children of them, so we have to
+        // special-case it
+        /* istanbul ignore else */
+        if (this.partOf instanceof OneOf) {
+            var lexicalParentFeaturesCopy = Object.assign({}, this.partOf._features);
+            this._features = Object.assign(lexicalParentFeaturesCopy, protoFeatures || {});
+        } else if (this.declaringField) {
+            // Skip feature resolution of sister fields.
+        } else if (this.parent) {
+            var parentFeaturesCopy = Object.assign({}, this.parent._features);
+            this._features = Object.assign(parentFeaturesCopy, protoFeatures || {});
+        } else {
+            throw new Error("Unable to find a parent for " + this.fullName);
+        }
     }
     if (this.extensionField) {
         // Sister fields should have the same features as their extensions.

src/parse.js

@@ -447,7 +447,7 @@ function parse(source, root, options) {
     function parseField(parent, rule, extend) {
         var type = next();
         if (type === "group") {
-            parseGroup(parent, rule);
+            parseGroup(parent, rule, extend);
             return;
         }
         // Type names can consume multiple tokens, in multiple variants:
@@ -504,7 +504,7 @@ function parse(source, root, options) {
         }
     }
 
-    function parseGroup(parent, rule) {
+    function parseGroup(parent, rule, extend) {
         if (edition >= 2023) {
             throw illegal("group");
         }
@@ -521,7 +521,7 @@ function parse(source, root, options) {
         var id = parseId(next());
         var type = new Type(name);
         type.group = true;
-        var field = new Field(fieldName, id, name, rule);
+        var field = new Field(fieldName, id, name, rule, extend);
         field.filename = parse.filename;
         ifBlock(type, function parseGroup_block(token) {
             switch (token) {
@@ -584,6 +584,10 @@ function parse(source, root, options) {
         });
         parent.add(type)
               .add(field);
+        if (parent === ptr) {
+            topLevelObjects.push(type);
+            topLevelObjects.push(field);
+        }
     }
 
     function parseMapField(parent) {

tests/comp_groups.js

@@ -16,6 +16,16 @@ var protoRepeated = "message Test {\
     };\
 }";
 
+var protoExtension = "syntax = \"proto2\";\
+message Message {\
+    extensions 100 to max;\
+}\
+extend Message {\
+    optional group GroupField = 100 {\
+        optional uint32 a = 101;\
+    }\
+}";
+
 tape.test("legacy groups", function(test) {
     var root = protobuf.parse(protoRequired).root.resolveAll();
 
@@ -159,3 +169,23 @@ tape.test("delimited encoding", function(test) {
 
     test.end();
 });
+
+tape.test("extension groups", function(test) {
+    var root = protobuf.parse(protoExtension).root.resolveAll();
+
+    var Message = root.lookupType("Message");
+    var GroupField = root.get("groupField");
+    var ExtensionField = Message.get(GroupField.fullName);
+    var msg = {};
+    msg[GroupField.fullName] = {
+        a: 111
+    };
+
+    test.equal(ExtensionField.declaringField, GroupField, "should add the sister field to the extended type");
+    test.equal(ExtensionField.delimited, true, "should use delimited encoding on the sister field");
+
+    var buf = Message.encode(msg).finish();
+    test.same(Array.prototype.slice.call(buf), [ 163, 6, 168, 6, 111, 164, 6 ], "should encode as a group");
+    test.same(Message.decode(buf), msg, "and decode back the original message");
+    test.end();
+});