Scripts: fix test chain reset script

scripts/gen_genesis.ml

@@ -14,6 +14,7 @@
 #mod_use "../src/lib_stdlib/utils.ml";;
 #mod_use "../src/lib_crypto/base58.ml";;
 
+open Lwt.Infix;;
 
 let prefix = "BLockGenesisGenesisGenesisGenesisGenesis"
 let rec genesis () =
@@ -30,8 +31,15 @@ let rec genesis () =
 let genesis, date = genesis ()
 
 let () =
-  Lwt_main.run (Lwt_io.lines_to_file "alphanet_version"
-                  (Lwt_stream.of_list [date]))
+  Lwt_main.run @@
+  let stream = Lwt_io.lines_of_file "alphanet_version" in
+  Lwt_stream.to_list stream >>= function
+  | [] | _ :: _ :: _ -> failwith "bad alphanet_version file"
+  | [ line ] -> match String.split_on_char 'Z' line with
+    | [ _ ; branch ] ->
+        let contents = if String.trim branch = "" then date else date ^ branch in
+        Lwt_io.lines_to_file "alphanet_version" (Lwt_stream.of_list [ contents ])
+    | _ -> failwith "bad alphanet_version file"
 
 let sed =
   Format.sprintf
@@ -47,8 +55,8 @@ let _ =
 
 let sed =
   Format.sprintf
-    "sed -i \
-     -e 's/name = \"TEZOS[^\"]*\" ;/name = \"TEZOS_%s\" ;/' \
+    "sed -E -i \
+     -e 's/name = \"(TEZOS[A_Z]+)[^\"]*\" ;/name = \"\\1%s\" ;/' \
      ../src/lib_shell/distributed_db_message.ml"
     date