Fix non-tail fail avoidance

src/passes/9-self_michelson/dune

@@ -6,7 +6,8 @@
     tezos-utils
   )
   (preprocess
-    (pps ppx_let bisect_ppx --conditional)
+    (pps ppx_let bisect_ppx --conditional ppx_expect)
   )
+  (inline_tests)
   (flags (:standard -w +1..62-4-9-44-40-42-48-30@39@33 -open Simple_utils ))
 )

src/passes/9-self_michelson/self_michelson.ml

@@ -382,14 +382,28 @@ let rec opt_tail_fail : michelson -> michelson =
      let rec aux args =
        match args with
        | [] -> []
-       | arg :: _ when is_failing arg -> [arg]
-       | arg :: args -> arg :: aux args in
-     let args = aux args in
-     Seq (l, List.map opt_tail_fail args)
+       | arg :: args ->
+         let arg = opt_tail_fail arg in
+         if is_failing arg
+         then [arg]
+         else arg :: aux args in
+     Seq (l, aux args)
   | Prim (l, p, args, annot) ->
      Prim (l, p, List.map opt_tail_fail args, annot)
   | x -> x
 
+let%expect_test _ =
+  let seq args = Seq(-1, args) in
+  let prim p args = Prim(-1, p, args, []) in
+  let code = seq [ prim I_IF_LEFT [ seq [ prim I_FAILWITH [] ; prim I_DROP [] ]
+                                  ; seq [ prim I_FAILWITH [] ; prim I_DROP [] ]
+                                  ]
+                 ; prim I_DROP []
+                 ] in
+  let code = opt_tail_fail code in
+  Format.printf "%a" Tezos_utils.Michelson.pp code ;
+  [%expect {| { IF_LEFT { FAILWITH } { FAILWITH } } |}]
+
 let rec opt_combine_drops (x : michelson) : michelson =
   let rec combine : michelson list -> michelson list = function
     | [] -> []