feat: parse universal type variables in signature items

CHANGES.md

@@ -30,6 +30,8 @@
   [#2790](https://github.com/reasonml/reason/pull/2790))
 - Support quoted extensions (@anmonteiro,
   [#2794](https://github.com/reasonml/reason/pull/2794))
+- Parse universal type variables in signature items (@anmonteiro,
+  [#2797](https://github.com/reasonml/reason/pull/2797))
 
 ## 3.12.0
 

src/reason-parser/reason_parser.mly

@@ -1931,7 +1931,7 @@ signature:
 
 signature_item:
   | item_attributes
-    LET item_extension_sugar? as_loc(val_ident) COLON core_type
+    LET item_extension_sugar? as_loc(val_ident) COLON poly_type
     { let loc = mklocation $startpos($2) $endpos in
       wrap_sig_ext
         ~loc

test/general-syntax-re.t/input.re

@@ -1322,3 +1322,7 @@ let () = {
   3
 };
 
+module type x = {
+  let a: 'a. 'a => unit;
+};
+

test/general-syntax-re.t/run.t

@@ -1545,3 +1545,7 @@ Format general implementation syntax
     let x = 1;
     3;
   };
+
+  module type x = {
+    let a: 'a. 'a => unit;
+  };

test/general-syntax-rei.t/input.rei

@@ -71,3 +71,10 @@ open! %foo Bar;
 type%foo t = int;
 
 type%x foo += Int;
+
+module type x = {
+  let a: 'a. 'a => unit;
+};
+
+let a: 'a. 'a => unit;
+

test/general-syntax-rei.t/run.t

@@ -82,3 +82,9 @@ Format general interface syntax
 
   type%x foo +=
     | Int;
+
+  module type x = {
+    let a: 'a. 'a => unit;
+  };
+
+  let a: 'a. 'a => unit;