No longer generate approximate merlin files

CHANGES.md

@@ -136,6 +136,11 @@ Unreleased
 - Remove `dune compute`. It was broken and unused (#4540,
   @jeremiedimino)
 
+- No longer generate an approximate merlin files when computing the
+  ocaml flags fails, for instance because they include the contents of
+  a file that failed to build. This was a niche feature and it was
+  getting in the way of making Dune's core better. (#4607, @jeremiedimino)
+
 2.9.0 (unreleased)
 ------------------
 

src/dune_engine/action_builder.ml

@@ -30,7 +30,6 @@ module T = struct
     | Dyn_deps : ('a * Dep.Set.t) t -> 'a t
     | Fail : fail -> _ t
     | Memo : 'a memo -> 'a t
-    | Catch : 'a t * 'a -> 'a t
     | Deps : Dep.Set.t -> unit t
     | Memo_build : 'a Memo.Build.t -> 'a t
     | Dyn_memo_build : 'a Memo.Build.t t -> 'a t
@@ -122,8 +121,6 @@ let env_var s = Deps (Dep.Set.singleton (Dep.env s))
 
 let alias a = dep (Dep.alias a)
 
-let catch t ~on_error = Catch (t, on_error)
-
 let contents p = Contents p
 
 let lines_of p = Lines_of p
@@ -380,10 +377,6 @@ struct
         Build_deps.file_exists p >>= function
         | true -> exec then_
         | false -> exec else_)
-      | Catch (t, on_error) -> (
-        Memo.Build.swallow_errors (fun () -> exec t) >>| function
-        | Ok r -> r
-        | Error () -> (on_error, Dep.Map.empty))
       | Memo m -> Memo_poly.eval m
       | Memo_build f ->
         let+ f = f in
@@ -450,7 +443,6 @@ let rec can_eval_statically : type a. a t -> bool = function
   | Fail _ -> true
   | If_file_exists (_, _, _) -> false
   | Memo _ -> false
-  | Catch (t, _) -> can_eval_statically t
   | Memo_build _ -> false
   | Dyn_memo_build _ -> false
   | Bind _ ->
@@ -518,9 +510,6 @@ let static_eval =
     | Fail { fail } -> fail ()
     | If_file_exists (_, _, _) -> assert false
     | Memo _ -> assert false
-    | Catch (t, v) -> (
-      try loop t acc with
-      | _ -> (v, Dep.Set.empty))
     | Memo_build _ -> assert false
     | Dyn_memo_build _ -> assert false
     | Bind _ -> assert false

src/dune_engine/action_builder.mli

@@ -154,10 +154,6 @@ val dyn_path_set : ('a * Path.Set.t) t -> 'a t
 
 val dyn_path_set_reuse : Path.Set.t t -> Path.Set.t t
 
-(** [catch t ~on_error] evaluates to [on_error] if an exception is raised during
-    the evaluation of [t]. *)
-val catch : 'a t -> on_error:'a -> 'a t
-
 (** [contents path] returns a description that when run will return the contents
     of the file at [path]. *)
 val contents : Path.t -> string t

src/dune_rules/merlin.ml

@@ -246,7 +246,7 @@ module Unprocessed = struct
     let config =
       { stdlib_dir
       ; requires
-      ; flags = Action_builder.catch flags ~on_error:[]
+      ; flags
       ; preprocess
       ; libname
       ; source_dirs

src/memo/memo.ml

@@ -53,12 +53,6 @@ module Build0 = struct
 
   let of_reproducible_fiber = Fun.id
 
-  let swallow_errors f =
-    Fiber.map_reduce_errors
-      (module Monoid.Unit)
-      f
-      ~on_error:(fun _ -> Fiber.return ())
-
   module Option = struct
     let iter option ~f =
       match option with

src/memo/memo.mli

@@ -77,10 +77,6 @@ module Build : sig
   end
   [@@inline always]
 
-  (** [swallow_errors f] swallows any error raised during the execution of [f].
-      Use this function if you are ok with a computation failing. *)
-  val swallow_errors : (unit -> 'a t) -> ('a, unit) Result.t t
-
   module Option : sig
     val iter : 'a option -> f:('a -> unit t) -> unit t