Use -output-complete-exe if available

src/dune/exe.ml

@@ -12,6 +12,12 @@ module Program = struct
     }
 end
 
+let custom_or_output_complete_exe ctx =
+  if Ocaml_version.supports_output_complete_exe ctx.Context.version then
+    "-output-complete-exe"
+  else
+    "-custom"
+
 module Linkage = struct
   type t =
     { mode : Mode.t
@@ -23,11 +29,15 @@ module Linkage = struct
 
   let native = { mode = Native; ext = ".exe"; flags = [] }
 
-  let custom = { mode = Byte; ext = ".exe"; flags = [ "-custom" ] }
+  let custom context =
+    { mode = Byte
+    ; ext = ".exe"
+    ; flags = [ custom_or_output_complete_exe context ]
+    }
 
   let native_or_custom (context : Context.t) =
     match context.ocamlopt with
-    | None -> custom
+    | None -> custom context
     | Some _ -> native
 
   let js = { mode = Byte; ext = ".bc.js"; flags = [] }
@@ -83,7 +93,7 @@ module Linkage = struct
       | Js -> []
       | Exe -> (
         match (wanted_mode, real_mode) with
-        | Native, Byte -> [ "-custom" ]
+        | Native, Byte -> [ custom_or_output_complete_exe ctx ]
         | _ -> [] )
       | Object -> o_flags
       | Shared_object -> (

src/dune/exe.mli

@@ -18,8 +18,9 @@ module Linkage : sig
   (** Native compilation, extension [.exe] *)
   val native : t
 
-  (** Byte compilation, link with [-custom], extension [.exe] *)
-  val custom : t
+  (** Byte compilation, link with [-custom] or [-output-complete-exe],
+      extension [.exe] *)
+  val custom : Context.t -> t
 
   (** [native] if supported, [custom] if not *)
   val native_or_custom : Context.t -> t

src/dune/exe_rules.ml

@@ -73,7 +73,7 @@ let executables_rules ~sctx ~dir ~expander ~dir_contents ~scope ~compile_info
       && (not (L.Set.mem exes.modes L.native))
       && not (L.Set.mem exes.modes L.exe)
     then
-      Exe.Linkage.custom :: l
+      Exe.Linkage.custom ctx :: l
     else
       l
   in

src/dune/ocaml_version.ml

@@ -31,3 +31,5 @@ let ooi_supports_no_approx version = version >= (4, 05, 0)
 let ooi_supports_no_code version = version >= (4, 05, 0)
 
 let supports_let_syntax version = version >= (4, 08, 0)
+
+let supports_output_complete_exe version = version >= (4, 10, 0)

src/dune/ocaml_version.mli

@@ -47,3 +47,6 @@ val ooi_supports_no_code : t -> bool
 
 (** Whether the language supports custom let operators *)
 val supports_let_syntax : t -> bool
+
+(** Does this support [-output-complete-exe]? *)
+val supports_output_complete_exe : t -> bool

src/dune/toplevel.ml

@@ -80,7 +80,7 @@ let setup_module_rules t =
   Super_context.add_rule sctx ~dir main_ml
 
 let setup_rules t =
-  let linkage = Exe.Linkage.custom in
+  let linkage = Exe.Linkage.custom (Compilation_context.context t.cctx) in
   let program = Source.program t.source in
   let sctx = Compilation_context.super_context t.cctx in
   Exe.build_and_link t.cctx ~program ~linkages:[ linkage ]