Fix Ppxlib.really_recursive and type_is_recursive

Those used to recurse into attributes, sometimes falsly returning
`Recursive`.

Signed-off-by: Nathan Rebours <nathan.p.rebours@gmail.com>

CHANGES.md

@@ -15,6 +15,10 @@ unreleased
 
 - Improve error messages in ppx raised exceptions (#292, @panglesd)
 
+- Fix a bug in `type_is_recursive` and `really_recursive` where they would
+  consider a type declaration recursive if the type appeared inside an attribute
+  payload (#299, @NathanReb)
+
 0.23.0 (31/08/2021)
 -------------------
 

src/common.ml

@@ -100,6 +100,9 @@ class type_is_recursive rec_flag tds =
       | Pcstr_tuple args -> List.iter args ~f:self#core_type
       | Pcstr_record fields -> List.iter fields ~f:self#label_declaration
 
+    method! attributes _ = (* Don't recurse through attributes *)
+                           ()
+
     method go () =
       match rec_flag with
       | Nonrecursive -> Nonrecursive

test/type_is_recursive/test.ml

@@ -59,7 +59,7 @@ val actually_recursive : rec_flag = Ppxlib__.Import.Recursive
 let ignore_attributes = test_is_recursive [%stri type t = int [@attr: t]]
 
 [%%expect{|
-val ignore_attributes : rec_flag = Ppxlib__.Import.Recursive
+val ignore_attributes : rec_flag = Ppxlib__.Import.Nonrecursive
 |}]
 
 (* Should be Recursive