more robust detection of lwt's version

src/client/lwt/dune

@@ -9,6 +9,7 @@
   Opentelemetry_client
   -open
   Opentelemetry_atomic)
+ (modules :standard \ gen_types_)
  (optional) ; lwt
  (libraries
   opentelemetry.util
@@ -26,18 +27,13 @@
   lwt.unix)
  (synopsis "Lwt-specific helpers for opentelemetry-client"))
 
-(rule
- (enabled_if
-  (and
-   %{lib-available:lwt}
-   (>= %{version:lwt} 6.0)))
- (action
-  (copy types_.ml.6 types_.ml)))
+(executable
+ (name gen_types_)
+ (modules gen_types_))
 
 (rule
- (enabled_if
-  (and
-   %{lib-available:lwt}
-   (< %{version:lwt} 6.0)))
+ (enabled_if %{lib-available:lwt})
+ (deps types_.ml.5 types_.ml.6)
+ (target types_.ml)
  (action
-  (copy types_.ml.5 types_.ml)))
+  (run ./gen_types_.exe %{version:lwt})))

src/client/lwt/gen_types_.ml

@@ -0,0 +1,23 @@
+let copy_file src dst =
+  let ic = open_in src in
+  let oc = open_out dst in
+  let buf = Bytes.create 1024 in
+  (try
+     while true do
+       let n = input ic buf 0 (Bytes.length buf) in
+       if n = 0 then raise End_of_file;
+       output oc buf 0 n
+     done
+   with End_of_file -> ());
+  close_in ic;
+  close_out oc
+
+let () =
+  let version = Sys.argv.(1) in
+  let major =
+    try Scanf.sscanf version "%d.%s" (fun maj _ -> maj) with _ -> 0
+  in
+  if major >= 6 then
+    copy_file "types_.ml.6" "types_.ml"
+  else
+    copy_file "types_.ml.5" "types_.ml"