Annotate struct definitions with a recursive flag.

test/libsolidity/syntaxTests/structs/recursion/recursive_struct_function_pointer.sol

@@ -0,0 +1,10 @@
+pragma experimental ABIEncoderV2;
+contract C {
+    struct S {
+        uint a;
+        function() external returns (S memory) sub;
+    }
+    function f() public pure returns (S memory) {
+    }
+}
+// ----