From 74b72bb44fdbe1a7548d02682c2b7fa22ef30d93 Mon Sep 17 00:00:00 2001
From: Rudi Grinberg <me@rgrinberg.com>
Date: Sat, 26 Oct 2024 09:32:04 +0100
Subject: [PATCH] test: reproduce #186 (#553)

---
 lib/posix.ml                |  7 ++++
 lib/posix.mli               |  5 +++
 lib_test/expect/test_186.ml | 76 +++++++++++++++++++++++++++++++++++++
 3 files changed, 88 insertions(+)
 create mode 100644 lib_test/expect/test_186.ml

diff --git a/lib/posix.ml b/lib/posix.ml
index 517f3266..1a551e00 100644
--- a/lib/posix.ml
+++ b/lib/posix.ml
@@ -151,5 +151,12 @@ let re ?(opts = []) s =
   r
 ;;
 
+let re_result ?opts s =
+  match re ?opts s with
+  | s -> Ok s
+  | exception Not_supported -> Error `Not_supported
+  | exception Parse_error -> Error `Parse_error
+;;
+
 let compile re = Re.compile (Re.longest re)
 let compile_pat ?(opts = []) s = compile (re ~opts s)
diff --git a/lib/posix.mli b/lib/posix.mli
index 74173ad8..a2213b0d 100644
--- a/lib/posix.mli
+++ b/lib/posix.mli
@@ -63,6 +63,11 @@ type opt =
 (** Parsing of a Posix extended regular expression *)
 val re : ?opts:opt list -> string -> Core.t
 
+val re_result
+  :  ?opts:opt list
+  -> string
+  -> (Core.t, [ `Not_supported | `Parse_error ]) result
+
 (** [compile r] is defined as [Core.compile (Core.longest r)] *)
 val compile : Core.t -> Core.re
 
diff --git a/lib_test/expect/test_186.ml b/lib_test/expect/test_186.ml
new file mode 100644
index 00000000..a177df6a
--- /dev/null
+++ b/lib_test/expect/test_186.ml
@@ -0,0 +1,76 @@
+open Import
+
+let print re result =
+  Printf.printf
+    "%s: %s\n"
+    re
+    (match result with
+     | Ok _ -> "backward range parsed"
+     | Error `Parse_error -> "parse error"
+     | Error `Not_supported -> "not supported")
+;;
+
+let cases = [ "[1-0]"; "[5-1]"; "[6-6]"; "[z-a]"; "[b-b]" ]
+
+let test f =
+  List.iter cases ~f:(fun re ->
+    let result = f re in
+    print re result)
+;;
+
+let%expect_test "perl" =
+  test Re.Perl.re_result;
+  [%expect
+    {|
+    [1-0]: backward range parsed
+    [5-1]: backward range parsed
+    [6-6]: backward range parsed
+    [z-a]: backward range parsed
+    [b-b]: backward range parsed
+    |}]
+;;
+
+let%expect_test "pcre" =
+  test Re.Pcre.re_result;
+  [%expect
+    {|
+    [1-0]: backward range parsed
+    [5-1]: backward range parsed
+    [6-6]: backward range parsed
+    [z-a]: backward range parsed
+    [b-b]: backward range parsed
+    |}]
+;;
+
+let%expect_test "posix" =
+  test Re.Posix.re_result;
+  [%expect
+    {|
+    [1-0]: backward range parsed
+    [5-1]: backward range parsed
+    [6-6]: backward range parsed
+    [z-a]: backward range parsed
+    [b-b]: backward range parsed
+    |}]
+;;
+
+(* CR-someday rgrinberg: is this correct? *)
+let%expect_test "emacs" =
+  test Re.Emacs.re_result;
+  [%expect
+    {|
+    [1-0]: backward range parsed
+    [5-1]: backward range parsed
+    [6-6]: backward range parsed
+    [z-a]: backward range parsed
+    [b-b]: backward range parsed
+    |}]
+;;
+
+(* We allow backward ranges in re. We could forbid them? *)
+let%expect_test "re" =
+  Format.printf "%a@." Re.pp (Re.rg '5' '0');
+  [%expect {| (Set 48-53) |}];
+  Format.printf "%a@." Re.pp (Re.rg '0' '5');
+  [%expect {| (Set 48-53) |}]
+;;