Correct order of printed quantified type vars (#2126)

Author: ncik-roberts

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
 |}]
 
 

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>
 |}]

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>
 |}]

ocaml/typing/printtyp.ml

@@ -1549,6 +1549,10 @@ 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