Annotate struct definitions with a recursive flag.

test/libsolidity/SolidityTypes.cpp

@@ -184,6 +184,7 @@ BOOST_AUTO_TEST_CASE(type_identifiers)
 	BOOST_CHECK_EQUAL(ContractType(c, true).identifier(), "t_super$_MyContract$$$_$2");
 
 	StructDefinition s(++id, {}, make_shared<string>("Struct"), {});
+	s.annotation().recursive = false;
 	BOOST_CHECK_EQUAL(s.type()->identifier(), "t_type$_t_struct$_Struct_$3_storage_ptr_$");
 
 	EnumDefinition e(++id, {}, make_shared<string>("Enum"), {});

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) {
+    }
+}
+// ----

test/libsolidity/syntaxTests/types/mapping/function_type_argument_external.sol

@@ -4,4 +4,3 @@ contract C {
 }
 // ----
 // TypeError: (37-64): Data location must be "memory" for parameter in function, but "storage" was given.
-// TypeError: (37-64): Internal type cannot be used for external function type.

test/libsolidity/syntaxTests/types/mapping/function_type_return_external.sol

@@ -4,4 +4,3 @@ contract C {
 }
 // ----
 // TypeError: (57-84): Data location must be "memory" for return parameter in function, but "storage" was given.
-// TypeError: (57-84): Internal type cannot be used for external function type.