Use a dune-project option instead of a new syntax

src/dune_engine/dune_project.ml

@@ -143,6 +143,7 @@ type t =
   ; accept_alternative_dune_file_name : bool
   ; generate_opam_files : bool
   ; use_standard_c_and_cxx_flags : bool option
+  ; enable_project_indexation : bool
   ; file_key : File_key.t
   ; dialects : Dialect.DB.t
   ; explicit_js_mode : bool
@@ -182,6 +183,8 @@ let set_generate_opam_files generate_opam_files t =
 
 let use_standard_c_and_cxx_flags t = t.use_standard_c_and_cxx_flags
 
+let enable_project_indexation t = t.enable_project_indexation
+
 let dialects t = t.dialects
 
 let set_dialects dialects t = { t with dialects }
@@ -207,6 +210,7 @@ let to_dyn
     ; accept_alternative_dune_file_name
     ; generate_opam_files
     ; use_standard_c_and_cxx_flags
+    ; enable_project_indexation
     ; file_key
     ; dialects
     ; explicit_js_mode
@@ -234,6 +238,7 @@ let to_dyn
       , bool accept_alternative_dune_file_name )
     ; ("generate_opam_files", bool generate_opam_files)
     ; ("use_standard_c_and_cxx_flags", option bool use_standard_c_and_cxx_flags)
+    ; ("enable_project_indexation", bool enable_project_indexation)
     ; ("file_key", string file_key)
     ; ("dialects", Dialect.DB.to_dyn dialects)
     ; ("explicit_js_mode", bool explicit_js_mode)
@@ -473,6 +478,8 @@ let expand_aliases_in_sandbox_default ~lang:_ = false
 let use_standard_c_and_cxx_flags_default ~(lang : Lang.Instance.t) =
   if lang.version >= (3, 0) then Some true else None
 
+let enable_project_indexation_default ~lang:_ = false
+
 let format_extension_key =
   Extension.register Format_config.syntax Format_config.dparse_args
     Format_config.to_dyn
@@ -511,6 +518,7 @@ let infer ~dir ?(info = Package.Info.empty) packages =
   let executables_implicit_empty_intf =
     executables_implicit_empty_intf_default ~lang
   in
+  let enable_project_indexation = enable_project_indexation_default ~lang in
   let explicit_js_mode = explicit_js_mode_default ~lang in
   let strict_package_deps = strict_package_deps_default ~lang in
   let cram = cram_default ~lang in
@@ -533,6 +541,7 @@ let infer ~dir ?(info = Package.Info.empty) packages =
   ; parsing_context
   ; generate_opam_files = false
   ; use_standard_c_and_cxx_flags = use_standard_c_and_cxx_flags_default ~lang
+  ; enable_project_indexation
   ; file_key
   ; dialects = Dialect.DB.builtin
   ; explicit_js_mode
@@ -597,6 +606,7 @@ let encode : t -> Dune_lang.t list =
      ; accept_alternative_dune_file_name
      ; generate_opam_files
      ; use_standard_c_and_cxx_flags
+     ; enable_project_indexation
      ; dialects
      ; explicit_js_mode
      ; format_config
@@ -656,6 +666,8 @@ let encode : t -> Dune_lang.t list =
                  (use_standard_c_and_cxx_flags_default ~lang))
           then Some (constr "use_standard_c_and_cxx_flags" bool b)
           else None)
+      ; flag' "enable_project_indexation" enable_project_indexation
+          enable_project_indexation_default
       ; (if Bool.equal cram (cram_default ~lang) then None
         else Some (constr "cram" Toggle.encode (Toggle.of_bool cram)))
       ; flag "expand_aliases_in_sandbox" expand_aliases_in_sandbox
@@ -752,6 +764,9 @@ let parse ~dir ~lang ~file ~dir_status =
         and+ use_standard_c_and_cxx_flags =
           field_o_b "use_standard_c_and_cxx_flags"
             ~check:(Dune_lang.Syntax.since Stanza.syntax (2, 8))
+        and+ enable_project_indexation =
+          field_o_b "enable_project_indexation"
+            ~check:(Dune_lang.Syntax.since Stanza.syntax (3, 5))
         and+ dialects =
           multi_field "dialect"
             (Dune_lang.Syntax.since Stanza.syntax (1, 11)
@@ -906,6 +921,10 @@ let parse ~dir ~lang ~file ~dir_status =
             | None -> use_standard_c_and_cxx_flags_default ~lang
             | some -> some
           in
+          let enable_project_indexation =
+            Option.value enable_project_indexation
+              ~default:(enable_project_indexation_default ~lang)
+          in
           let cram =
             match cram with
             | None -> cram_default ~lang
@@ -962,6 +981,7 @@ let parse ~dir ~lang ~file ~dir_status =
           ; accept_alternative_dune_file_name
           ; generate_opam_files
           ; use_standard_c_and_cxx_flags
+          ; enable_project_indexation
           ; dialects
           ; explicit_js_mode
           ; format_config

src/dune_engine/dune_project.mli

@@ -66,6 +66,8 @@ val set_generate_opam_files : bool -> t -> t
     compiler command line when building C stubs. *)
 val use_standard_c_and_cxx_flags : t -> bool option
 
+val enable_project_indexation : t -> bool
+
 val dialects : t -> Dialect.DB.t
 
 val set_dialects : Dialect.DB.t -> t -> t

src/dune_rules/uideps.ml

@@ -2,17 +2,7 @@ open Import
 module CC = Compilation_context
 module SC = Super_context
 
-let syntax =
-  let name = "project_indexation" in
-  let desc = "Enables project indexation" in
-  Dune_lang.Syntax.create ~name ~desc ~experimental:true
-    [ ((0, 1), `Since (3, 5)) ]
-
-let key =
-  let decoder = Dune_lang.Decoder.return ((), []) in
-  Dune_project.Extension.register syntax decoder Unit.to_dyn
-
-let activated project = Dune_project.is_extension_set project key
+let activated project = Dune_project.enable_project_indexation project
 
 let ocaml_uideps sctx ~dir =
   Super_context.resolve_program ~loc:None ~dir sctx "ocaml-uideps"
@@ -38,58 +28,59 @@ let build_path cctx =
       Lib_info.obj_dir info |> Obj_dir.byte_dir)
 
 let cctx_rules cctx =
-  (* Indexing is performed by the external binary [ocaml-uideps] which performs
-      full shape reduction to compute the actual definition of all the elements in
-      the typedtree. This step is therefore dependent on all the cmts of those
-      definitions are used by all the cmts of modules in this cctx.
-
-      TODO: this large set of dependencies is bad for parallelism, if shape
-      reduction was only partial a that point it might speed things a lot. *)
-  let dir = CC.dir cctx in
-  let modules =
-    CC.modules cctx |> Modules.fold_no_vlib ~init:[] ~f:(fun x acc -> x :: acc)
-  in
-  let sctx = CC.super_context cctx in
-  let obj_dir = CC.obj_dir cctx in
-  let cm_kind = Lib_mode.Cm_kind.(Ocaml Cmi) in
-  let modules_with_cmts =
-    List.filter_map
-      ~f:(fun module_ ->
-        Obj_dir.Module.cmt_file obj_dir ~ml_kind:Impl ~cm_kind module_
-        |> Option.map ~f:(fun cmt -> (module_, Path.build cmt)))
-      modules
-  in
-  let open Memo.O in
-  let* ocaml_uideps = ocaml_uideps sctx ~dir in
-  let context_dir =
-    CC.context cctx |> Context.name |> Context_name.build_dir |> Path.build
-  in
-  let* build_path = build_path cctx in
-  (* let all_cmts = List.map ~f:snd modules_with_cmts in *)
-  let intermediate_targets, intermediates =
-    List.fold_map modules_with_cmts ~init:[]
-      ~f:(fun targets (_module_, for_cmt) ->
-        let fn = uideps_path_in_obj_dir ~for_cmt obj_dir in
-        let action =
-          Command.run ~dir:context_dir ocaml_uideps
-            [ A "process-cmt"
-            ; A "-o"
-            ; Target fn
-            ; Dep for_cmt
-            ; As (List.map ~f:Path.to_absolute_filename build_path)
-              (* TODO ulysse: these deps are incorrect. Fixing it might improve
-                 performance by increasing parallelism. *)
-            (* ; Hidden_deps (Dep.Set.of_files all_cmts) *)
-            ]
-        in
-        (Path.build fn :: targets, action))
-  in
-  let fn = uideps_path_in_obj_dir obj_dir in
-  let aggregate =
-    Command.run ~dir:context_dir ocaml_uideps
-      [ A "aggregate"; A "-o"; Target fn; Deps intermediate_targets ]
-  in
-  SC.add_rules sctx ~dir (aggregate :: intermediates)
+  let project = Compilation_context.scope cctx |> Scope.project in
+  if not @@ activated project then Memo.return ()
+  else
+    (* Indexing is performed by the external binary [ocaml-uideps] which performs
+        full shape reduction to compute the actual definition of all the elements in
+        the typedtree. This step is therefore dependent on all the cmts of those
+        definitions are used by all the cmts of modules in this cctx. *)
+    let dir = CC.dir cctx in
+    let modules =
+      CC.modules cctx
+      |> Modules.fold_no_vlib ~init:[] ~f:(fun x acc -> x :: acc)
+    in
+    let sctx = CC.super_context cctx in
+    let obj_dir = CC.obj_dir cctx in
+    let cm_kind = Lib_mode.Cm_kind.(Ocaml Cmi) in
+    let modules_with_cmts =
+      List.filter_map
+        ~f:(fun module_ ->
+          Obj_dir.Module.cmt_file obj_dir ~ml_kind:Impl ~cm_kind module_
+          |> Option.map ~f:(fun cmt -> (module_, Path.build cmt)))
+        modules
+    in
+    let open Memo.O in
+    let* ocaml_uideps = ocaml_uideps sctx ~dir in
+    let context_dir =
+      CC.context cctx |> Context.name |> Context_name.build_dir |> Path.build
+    in
+    let* build_path = build_path cctx in
+    (* let all_cmts = List.map ~f:snd modules_with_cmts in *)
+    let intermediate_targets, intermediates =
+      List.fold_map modules_with_cmts ~init:[]
+        ~f:(fun targets (_module_, for_cmt) ->
+          let fn = uideps_path_in_obj_dir ~for_cmt obj_dir in
+          let action =
+            Command.run ~dir:context_dir ocaml_uideps
+              [ A "process-cmt"
+              ; A "-o"
+              ; Target fn
+              ; Dep for_cmt
+              ; As (List.map ~f:Path.to_absolute_filename build_path)
+                (* TODO ulysse: these deps are incorrect. Fixing it might improve
+                   performance by increasing parallelism. *)
+                (* ; Hidden_deps (Dep.Set.of_files all_cmts) *)
+              ]
+          in
+          (Path.build fn :: targets, action))
+    in
+    let fn = uideps_path_in_obj_dir obj_dir in
+    let aggregate =
+      Command.run ~dir:context_dir ocaml_uideps
+        [ A "aggregate"; A "-o"; Target fn; Deps intermediate_targets ]
+    in
+    SC.add_rules sctx ~dir (aggregate :: intermediates)
 
 let aggregate sctx ~dir ~target ~uideps =
   let open Memo.O in

test/blackbox-tests/test-cases/tuideps.t/dune-project

@@ -1,3 +1,4 @@
 (lang dune 3.5)
 (implicit_transitive_deps false)
-(using project_indexation 0.1)
+
+(enable_project_indexation)

test/blackbox-tests/test-cases/tuideps.t/run.t

@@ -5,7 +5,7 @@
 $ tree -a _build/default 
 
   $ dune clean
-  $ dune build 
+  $ dune build @uideps
 
   $ find . -name '*.uideps'
   ./_build/default/implicit-lib/.imp_lib.objs/.uideps