Change the type of Build.of_result and add Build.of_result_map

src/build.ml

@@ -172,9 +172,14 @@ let fail ?targets x =
   | None -> Fail x
   | Some l -> Targets l >>> Fail x
 
-let of_result = function
-  | Ok    x -> return x
-  | Error e -> fail { fail = fun () -> raise e }
+let of_result ?targets = function
+  | Ok    x -> x
+  | Error e -> fail ?targets { fail = fun () -> raise e }
+
+let of_result_map ?targets res ~f =
+  match res with
+  | Ok    x -> f x
+  | Error e -> fail ?targets { fail = fun () -> raise e }
 
 let memoize name t =
   Memo { name; t; state = Unevaluated }

src/build.mli

@@ -110,11 +110,20 @@ val if_file_exists : Path.t -> then_:('a, 'b) t -> else_:('a, 'b) t -> ('a, 'b)
 *)
 val file_exists_opt : Path.t -> ('a, 'b) t -> ('a, 'b option) t
 
-(** Always fail when executed. We pass a function rather than an exception to get a proper
-    backtrace *)
+(** Always fail when executed. We pass a function rather than an
+    exception to get a proper backtrace *)
 val fail : ?targets:Path.t list -> fail -> (_, _) t
 
-val of_result : ('a, exn) Result.t -> (unit, 'a) t
+val of_result
+  :  ?targets:Path.t list
+  -> (('a, 'b) t, exn) Result.t
+  -> ('a, 'b) t
+
+val of_result_map
+  : ?targets:Path.t list
+  -> ('a, exn) Result.t
+  -> f:('a -> ('b, 'c) t)
+  -> ('b, 'c) t
 
 (** [memoize name t] is an arrow that behaves like [t] except that its
     result is computed only once. *)

src/super_context.ml

@@ -272,7 +272,10 @@ module Libs = struct
 
   let requires t ~dir ~has_dot_merlin compile_info =
     add_select_rules t ~dir (Lib.Compile.resolved_selects compile_info);
-    let requires = Build.of_result (Lib.Compile.requires compile_info) in
+    let requires =
+      Build.of_result_map (Lib.Compile.requires compile_info)
+        ~f:Build.return
+    in
     let requires =
       Build.record_lib_deps (Lib.Compile.user_written_deps compile_info)
         ~kind:(if Lib.Compile.optional compile_info then