From ec43ce12c2c06adfd17711aaebd88f7e44da6a49 Mon Sep 17 00:00:00 2001
From: Nick Roberts <nroberts@janestreet.com>
Date: Tue, 5 Dec 2023 13:17:03 -0500
Subject: [PATCH] Correct order of printed quantified type vars

---
 ocaml/testsuite/tests/typing-layouts/annots.ml       | 10 +++++-----
 ocaml/testsuite/tests/typing-layouts/basics.ml       |  4 ++--
 ocaml/testsuite/tests/typing-layouts/basics_alpha.ml |  2 +-
 ocaml/typing/printtyp.ml                             |  4 ++++
 4 files changed, 12 insertions(+), 8 deletions(-)

diff --git a/ocaml/testsuite/tests/typing-layouts/annots.ml b/ocaml/testsuite/tests/typing-layouts/annots.ml
index 379ae4c50c9..19376c6ccee 100644
--- a/ocaml/testsuite/tests/typing-layouts/annots.ml
+++ b/ocaml/testsuite/tests/typing-layouts/annots.ml
@@ -226,8 +226,8 @@ let f : (_ : immediate) -> (_ : value) = fun _ -> assert false
 let g : (_ : value) -> (_ : immediate) = fun _ -> assert false
 
 [%%expect {|
-val f : 'b ('a : immediate). 'a -> 'b = <fun>
-val g : ('b : immediate) 'a. 'a -> 'b = <fun>
+val f : ('a : immediate) 'b. 'a -> 'b = <fun>
+val g : 'a ('b : immediate). 'a -> 'b = <fun>
 |}]
 
 (********************************************)
@@ -551,13 +551,13 @@ val f : ('a : immediate). 'a -> 'a = <fun>
 let f = fun x y (type (a : immediate)) (z : a) -> z
 
 [%%expect{|
-val f : ('a : immediate) 'c 'b. 'b -> 'c -> 'a -> 'a = <fun>
+val f : 'b 'c ('a : immediate). 'b -> 'c -> 'a -> 'a = <fun>
 |}]
 
 let f = fun x y (type a : immediate) (z : a) -> z
 
 [%%expect{|
-val f : ('a : immediate) 'c 'b. 'b -> 'c -> 'a -> 'a = <fun>
+val f : 'b 'c ('a : immediate). 'b -> 'c -> 'a -> 'a = <fun>
 |}]
 (* CR layouts: canonicalizing the order of quantification here
    would reduce wibbles in error messages *)
@@ -574,7 +574,7 @@ exception E : ('a : immediate) ('b : any). 'b t2_any * 'a list -> exn
 
 [%%expect{|
 type (_ : any) t2_any
-exception E : ('a : immediate) ('b : any). 'b t2_any * 'a list -> exn
+exception E : ('b : any) ('a : immediate). 'b t2_any * 'a list -> exn
 |}]
 
 
diff --git a/ocaml/testsuite/tests/typing-layouts/basics.ml b/ocaml/testsuite/tests/typing-layouts/basics.ml
index 721fef021c3..5f857be21e6 100644
--- a/ocaml/testsuite/tests/typing-layouts/basics.ml
+++ b/ocaml/testsuite/tests/typing-layouts/basics.ml
@@ -649,7 +649,7 @@ end;;
 module M11_3f :
   sig
     type ('a : float64) t = 'a
-    val foo : 'b ('a : float64). < usefloat : 'a t -> 'b; .. > -> 'a t -> 'b
+    val foo : ('a : float64) 'b. < usefloat : 'a t -> 'b; .. > -> 'a t -> 'b
   end
 |}];;
 
@@ -1265,7 +1265,7 @@ let q () =
     ()
 
 [%%expect{|
-val ( let* ) : 'b ('a : float64). 'a -> 'b -> unit = <fun>
+val ( let* ) : ('a : float64) 'b. 'a -> 'b -> unit = <fun>
 val ( and* ) : 'a -> 'b -> t_float64 = <fun>
 val q : unit -> unit = <fun>
 |}]
diff --git a/ocaml/testsuite/tests/typing-layouts/basics_alpha.ml b/ocaml/testsuite/tests/typing-layouts/basics_alpha.ml
index 0378d54be22..f29391a1889 100644
--- a/ocaml/testsuite/tests/typing-layouts/basics_alpha.ml
+++ b/ocaml/testsuite/tests/typing-layouts/basics_alpha.ml
@@ -1455,7 +1455,7 @@ let q () =
     ()
 
 [%%expect{|
-val ( let* ) : 'b ('a : float64). 'a -> 'b -> unit = <fun>
+val ( let* ) : ('a : float64) 'b. 'a -> 'b -> unit = <fun>
 val ( and* ) : 'a -> 'b -> t_float64 = <fun>
 val q : unit -> unit = <fun>
 |}]
diff --git a/ocaml/typing/printtyp.ml b/ocaml/typing/printtyp.ml
index be6eae91d8b..bef5e0c2280 100644
--- a/ocaml/typing/printtyp.ml
+++ b/ocaml/typing/printtyp.ml
@@ -1540,6 +1540,10 @@ let zap_qtvs_if_boring qtvs =
    This implements Case (C3) from Note [When to print jkind annotations]. *)
 let extract_qtvs tyl =
   let fvs = Ctype.free_non_row_variables_of_list tyl in
+  (* The [Ctype.free*variables] family of functions returns the free
+     variables in reverse order they were encountered in the list of types.
+  *)
+  let fvs = List.rev fvs in
   let tfvs = List.map Transient_expr.repr fvs in
   let vars_jkinds = tree_of_qtvs tfvs in
   zap_qtvs_if_boring vars_jkinds