Fix Array.of_seq (#1897)

Reported at https://caml.inria.fr/mantis/view.php?id=7820

Array.of_seq applies a circular permutation of one cell to the right
on the sequence.

With OCaml 4.07.0 and trunk, we have

- : int array = [|3; 1; 2|]

In stdlib/array.ml, line 337 (last line of of_rev_list), we have
      fill (len-1) tl
whereas it should be
      fill (len-2) tl
since hd, which should be assigned to the cell (len - 1), is skipped.

3 files changed, 18 insertions, 1 deletions

diff --git a/Changes b/Changes
index 25976617b3..62d549c017 100644
--- a/Changes
+++ b/Changes
@@ -1,3 +1,11 @@
+OCaml 4.07 maintenance branch
+-----------------------------
+
+- MPR#7820, GPR#1897: Fix Array.of_seq. This function used to apply a circular
+  permutation of one cell to the right on the sequence.
+  (Thierry Martinez, review by Nicolás Ojeda Bär)
+
+
 OCaml 4.07.0 (10 July 2018)
 ---------------------------
 
diff --git a/stdlib/array.ml b/stdlib/array.ml
index d29a04faab..a693f4a72f 100644
--- a/stdlib/array.ml
+++ b/stdlib/array.ml
@@ -334,7 +334,7 @@ let of_rev_list = function
           [] -> a
         | hd::tl -> unsafe_set a i hd; fill (i-1) tl
       in
-      fill (len-1) tl
+      fill (len-2) tl
 
 let of_seq i =
   let l = Seq.fold_left (fun acc x -> x::acc) [] i in
diff --git a/testsuite/tests/lib-seq/test.ml b/testsuite/tests/lib-seq/test.ml
index 934a001efb..ca38d4663c 100644
--- a/testsuite/tests/lib-seq/test.ml
+++ b/testsuite/tests/lib-seq/test.ml
@@ -13,6 +13,15 @@ let () =
   ()
 ;;  
 
+(* MPR 7820 *)
+let () =
+  assert
+    ([| 1;2;3 |] =
+      (Array.to_seq [| 1;2;3 |]
+      |> Array.of_seq));
+  ()
+;;
+
 let () = print_endline "OK";;