THRIFT-4060 add better support in the cpp generator for custom ostream operators on structures
Client: C++

This closes #1172
diff --git a/test/AnnotationTest.thrift b/test/AnnotationTest.thrift
index 191995a..7e24e1c 100644
--- a/test/AnnotationTest.thrift
+++ b/test/AnnotationTest.thrift
@@ -57,6 +57,15 @@
   "Winter"
 } ( foo = "bar" )
 
+struct ostr_default {
+  1: i32 bar;
+}
+
+struct ostr_custom {
+  1: i32 bar;
+} (cpp.customostream)
+
+
 service foo_service {
   void foo() ( foo = "bar" )
 } (a.b="c")