From 9709f88d5fa6c1b296bec05d70f9ba9cd6764180 Mon Sep 17 00:00:00 2001
From: Simon Cruanes <simon.cruanes.2007@m4x.org>
Date: Tue, 7 Nov 2023 20:38:27 -0500
Subject: [PATCH] breaking: fut: `join` does not take `?on` anymore

---
 src/fut.ml  | 12 ++++++++++--
 src/fut.mli |  2 +-
 2 files changed, 11 insertions(+), 3 deletions(-)

diff --git a/src/fut.ml b/src/fut.ml
index ad34cefe..0e235f77 100644
--- a/src/fut.ml
+++ b/src/fut.ml
@@ -123,7 +123,6 @@ let map ?on ~f fut : _ t =
          Error (e, bt))
     | Error e_bt -> Error e_bt
   in
-
   match peek fut with
   | Some r -> of_result (map_res r)
   | None ->
@@ -137,7 +136,17 @@ let map ?on ~f fut : _ t =
         match on with
         | None -> map_and_fulfill ()
         | Some on -> Runner.run_async on map_and_fulfill);
+    fut2
 
+let join (fut : 'a t t) : 'a t =
+  match peek fut with
+  | Some (Ok f) -> f
+  | Some (Error (e, bt)) -> fail e bt
+  | None ->
+    let fut2, promise = make () in
+    on_result fut (function
+      | Ok sub_fut -> on_result sub_fut (fulfill promise)
+      | Error _ as e -> fulfill promise e);
     fut2
 
 let bind ?on ~f fut : _ t =
@@ -175,7 +184,6 @@ let bind ?on ~f fut : _ t =
     fut2
 
 let bind_reify_error ?on ~f fut : _ t = bind ?on ~f (reify_error fut)
-let join ?on fut = bind ?on fut ~f:(fun x -> x)
 
 let update_ (st : 'a A.t) f : 'a =
   let rec loop () =
diff --git a/src/fut.mli b/src/fut.mli
index 99b04a8d..989d43a6 100644
--- a/src/fut.mli
+++ b/src/fut.mli
@@ -120,7 +120,7 @@ val bind_reify_error : ?on:Runner.t -> f:('a or_error -> 'b t) -> 'a t -> 'b t
     @param on if provided, [f] runs on the given runner
     @since 0.4 *)
 
-val join : ?on:Runner.t -> 'a t t -> 'a t
+val join : 'a t t -> 'a t
 (** [join fut] is [fut >>= Fun.id]. It joins the inner layer of the future.
     @since 0.2 *)