bind: copy documentation for interface methods to ObjC

Updates golang/go#25473

Change-Id: I63bf8dde15b0f108eabdc653b59039607b47a0aa
Reviewed-on: https://go-review.googlesource.com/114055
Reviewed-by: Hyang-Ah Hana Kim <hyangah@gmail.com>
diff --git a/bind/genobjc.go b/bind/genobjc.go
index d24a87d..d67f272 100644
--- a/bind/genobjc.go
+++ b/bind/genobjc.go
@@ -863,7 +863,8 @@
 }
 
 func (g *ObjcGen) genInterfaceInterface(obj *types.TypeName, summary ifaceSummary, isProtocol bool) {
-	g.objcdoc(g.docs[obj.Name()].Doc())
+	doc := g.docs[obj.Name()]
+	g.objcdoc(doc.Doc())
 	g.Printf("@interface %[1]s%[2]s : ", g.namePrefix, obj.Name())
 	if isErrorType(obj.Type()) {
 		g.Printf("NSError")
@@ -885,6 +886,7 @@
 			continue
 		}
 		s := g.funcSummary(nil, m)
+		g.objcdoc(doc.Member(m.Name()))
 		g.Printf("- %s;\n", s.asMethod(g))
 	}
 	g.Printf("@end\n")
diff --git a/bind/testdata/doc.objc.h.golden b/bind/testdata/doc.objc.h.golden
index bc2a2e8..614ba5c 100644
--- a/bind/testdata/doc.objc.h.golden
+++ b/bind/testdata/doc.objc.h.golden
@@ -127,6 +127,9 @@
 @property(strong, readonly) id _ref;
 
 - (instancetype)initWithRef:(id)ref;
+/**
+ * IM is a method.
+ */
 - (void)im;
 @end