flambda-backend: Fix toplevel printer for arrays of unboxed things (#2718)

* a fistful of tests printing arrays of unboxed nums

Signed-off-by: David Vulakh <dvulakh@janestreet.com>

* fix printer for arrays of unboxed things

Signed-off-by: David Vulakh <dvulakh@janestreet.com>

---------

Signed-off-by: David Vulakh <dvulakh@janestreet.com>

Author: dvulakh

testsuite/tests/tool-toplevel/exotic_arrays.compilers.reference

@@ -0,0 +1,6 @@
+val y : float array = [|1.; 2.; 3.; 4.|]
+val y : float# array = [|<abstr>; <abstr>; <abstr>; <abstr>|]
+val y : int32# array = <abstr array>
+val y : nativeint# array = <abstr array>
+val y : int64# array = <abstr array>
+

testsuite/tests/tool-toplevel/exotic_arrays.ml

@@ -0,0 +1,13 @@
+(* TEST
+  toplevel.opt;
+*)
+
+let y = [| 1.0; 2.0; 3.0; 4.0 |];;
+
+let y = [| #1.0; #2.0; #3.0; #4.0 |];;
+
+let y = [| #1l; #2l; #3l; #4l |];;
+
+let y = [| #1n; #2n; #3n; #4n |];;
+
+let y = [| #1L; #2L; #3L; #4L |];;

toplevel/genprintval.ml

@@ -620,25 +620,28 @@ module Make(O : OBJ)(EVP : EVALPATH with type valu = O.t) = struct
       tree_list start ty_list
 
       and tree_of_generic_array am depth obj ty_arg =
-        let oval elts = Oval_array (elts, am) in
-        let length = O.size obj in
-        if length > 0 then
-          match check_depth depth obj ty with
-            Some x -> x
-          | None ->
-              let rec tree_of_items tree_list i =
-                if !printer_steps < 0 || depth < 0 then
-                  Oval_ellipsis :: tree_list
-                else if i < length then
-                  let tree =
-                    nest tree_of_val (depth - 1) (O.field obj i) ty_arg
-                  in
-                  tree_of_items (tree :: tree_list) (i + 1)
-                else tree_list
-              in
-              oval (List.rev (tree_of_items [] 0))
+        if O.tag obj = Obj.custom_tag then
+          Oval_stuff "<abstr array>"
         else
-          oval []
+          let oval elts = Oval_array (elts, am) in
+          let length = O.size obj in
+          if length > 0 then
+            match check_depth depth obj ty with
+              Some x -> x
+            | None ->
+                let rec tree_of_items tree_list i =
+                  if !printer_steps < 0 || depth < 0 then
+                    Oval_ellipsis :: tree_list
+                  else if i < length then
+                    let tree =
+                      nest tree_of_val (depth - 1) (O.field obj i) ty_arg
+                    in
+                    tree_of_items (tree :: tree_list) (i + 1)
+                  else tree_list
+                in
+                oval (List.rev (tree_of_items [] 0))
+          else
+            oval []
 
       and tree_of_constr_with_args
              tree_of_cstr cstr_name inlined start depth obj ty_args unboxed =