Add build_context field to context

Now we create the build context only once per context

Signed-off-by: Rudi Grinberg <me@rgrinberg.com>

Author: rgrinberg

src/dune_rules/context.ml

@@ -97,16 +97,14 @@ module T = struct
     ; supports_shared_libraries : Dynlink_supported.By_the_os.t
     ; which : string -> Path.t option
     ; lib_config : Lib_config.t
+    ; build_context : Build_context.t
     }
 
   let equal x y = Context_name.equal x.name y.name
 
   let hash t = Context_name.hash t.name
 
-  let rec to_build_context
-      { name; build_dir; env; for_host; stdlib_dir; default_ocamlpath; _ } =
-    Build_context.create ~name ~build_dir ~env ~stdlib_dir ~default_ocamlpath
-      ~host:(Option.map ~f:to_build_context for_host)
+  let build_context t = t.build_context
 
   let to_dyn t : Dyn.t =
     let open Dyn.Encoder in
@@ -419,7 +417,7 @@ let create ~(kind : Kind.t) ~path ~env ~env_nodes ~name ~merlin ~targets
       | Error (Makefile_config file, msg) ->
         User_error.raise ~loc:(Loc.in_file file) [ Pp.text msg ]
     in
-    let* default_findlib_paths, (ocaml_config_vars, ocfg) =
+    let* default_ocamlpath, (ocaml_config_vars, ocfg) =
       Fiber.fork_and_join default_findlib_paths (fun () ->
           let+ lines =
             Process.run_capture_lines ~env Strict ocamlc [ "-config" ]
@@ -432,7 +430,7 @@ let create ~(kind : Kind.t) ~path ~env ~env_nodes ~name ~merlin ~targets
               (vars, ocfg)
             | Error msg -> Error (Ocamlc_config, msg) ))
     in
-    let findlib_paths = ocamlpath @ default_findlib_paths in
+    let findlib_paths = ocamlpath @ default_ocamlpath in
     let version = Ocaml_version.of_ocaml_config ocfg in
     let env =
       (* See comment in ansi_color.ml for setup_env_for_colors. For versions
@@ -473,7 +471,7 @@ let create ~(kind : Kind.t) ~path ~env ~env_nodes ~name ~merlin ~targets
         ; ( "DUNE_OCAML_HARDCODED"
           , String.concat
               ~sep:(Char.escaped ocamlpath_sep)
-              (List.map ~f:Path.to_string default_findlib_paths) )
+              (List.map ~f:Path.to_string default_ocamlpath) )
         ; extend_var "OCAMLTOP_INCLUDE_PATH"
             (Path.Build.relative local_lib_root "toplevel")
         ; extend_var "OCAMLFIND_IGNORE_DUPS_IN" ~path_sep:ocamlpath_sep
@@ -545,6 +543,11 @@ let create ~(kind : Kind.t) ~path ~env ~env_nodes ~name ~merlin ~targets
       supports_shared_libraries && dynamically_linked_foreign_archives
     in
     let t =
+      let build_context =
+        Build_context.create ~name ~build_dir ~env ~stdlib_dir
+          ~default_ocamlpath
+          ~host:(Option.map host ~f:(fun c -> c.build_context))
+      in
       { name
       ; implicit
       ; kind
@@ -570,7 +573,7 @@ let create ~(kind : Kind.t) ~path ~env ~env_nodes ~name ~merlin ~targets
       ; env
       ; findlib = Findlib.create ~paths:findlib_paths ~lib_config
       ; findlib_toolchain
-      ; default_ocamlpath = default_findlib_paths
+      ; default_ocamlpath
       ; arch_sixtyfour
       ; install_prefix
       ; stdlib_dir
@@ -581,6 +584,7 @@ let create ~(kind : Kind.t) ~path ~env ~env_nodes ~name ~merlin ~targets
           Dynlink_supported.By_the_os.of_bool supports_shared_libraries
       ; which
       ; lib_config
+      ; build_context
       }
     in
     if Ocaml_version.supports_response_file version then (

src/dune_rules/context.mli

@@ -94,6 +94,7 @@ type t = private
         (** Given a program name, e.g. ["ocaml"], find the path to a preferred
             executable in PATH, e.g. [Some "/path/to/ocaml.opt.exe"]. *)
   ; lib_config : Lib_config.t
+  ; build_context : Build_context.t
   }
 
 val equal : t -> t -> bool
@@ -130,7 +131,7 @@ val lib_config : t -> Lib_config.t
     the host build context. Otherwise, it just returns [exe]. *)
 val map_exe : t -> Path.t -> Path.t
 
-val to_build_context : t -> Build_context.t
+val build_context : t -> Build_context.t
 
 val init_configurator : t -> unit
 

src/dune_rules/dep_conf_eval.ml

@@ -50,7 +50,7 @@ let dep expander = function
              | Some pkg ->
                Build.alias
                  (Build_system.Alias.package_install
-                    ~context:(Context.to_build_context context)
+                    ~context:(Context.build_context context)
                     ~pkg)
              | None ->
                Build.fail

src/dune_rules/install_rules.ml

@@ -741,23 +741,20 @@ let install_rules sctx (package : Package.t) =
           ]
   in
   let () =
+    let context = Context.build_context ctx in
     let target_alias =
-      Build_system.Alias.package_install
-        ~context:(Context.to_build_context ctx)
-        ~pkg:package
+      Build_system.Alias.package_install ~context ~pkg:package
     in
     Rules.Produce.Alias.add_deps target_alias files
       ~dyn_deps:
         (let+ packages = packages in
          Package.Id.Set.to_list packages
          |> Path.Set.of_list_map ~f:(fun (pkg : Package.Id.t) ->
-                let name = Package.Id.name pkg in
                 let pkg =
+                  let name = Package.Id.name pkg in
                   Package.Name.Map.find_exn (Super_context.packages sctx) name
                 in
-                Build_system.Alias.package_install
-                  ~context:(Context.to_build_context ctx)
-                  ~pkg
+                Build_system.Alias.package_install ~context ~pkg
                 |> Alias.stamp_file |> Path.build))
   in
   let action =

src/dune_rules/main.ml

@@ -80,7 +80,7 @@ let init_build_system ?only_packages ~sandboxing_preference ?caching w =
     Artifact_substitution.copy_file ?chmod ~src ~dst ~conf ()
   in
   Build_system.init ~sandboxing_preference ~promote_source
-    ~contexts:(List.map ~f:Context.to_build_context w.contexts)
+    ~contexts:(List.map ~f:Context.build_context w.contexts)
     ?caching ();
   List.iter w.contexts ~f:Context.init_configurator;
   let+ scontexts = Gen_rules.gen w.conf ~contexts:w.contexts ?only_packages in

src/dune_rules/super_context.ml

@@ -292,7 +292,7 @@ let make_rule t ?sandbox ?mode ?locks ?loc ~dir build =
   let build = chdir_to_build_context_root t build in
   let env = get_node t.env_tree ~dir |> Env_node.external_env in
   Rule.make ?sandbox ?mode ?locks ~info:(Rule.Info.of_loc_opt loc)
-    ~context:(Some (Context.to_build_context t.context))
+    ~context:(Some (Context.build_context t.context))
     ~env:(Some env) build
 
 let add_rule t ?sandbox ?mode ?locks ?loc ~dir build =
@@ -310,7 +310,7 @@ let add_rules t ?sandbox ~dir builds =
 let add_alias_action t alias ~dir ~loc ?locks ~stamp action =
   let env = Some (get_node t.env_tree ~dir |> Env_node.external_env) in
   Rules.Produce.Alias.add_action
-    ~context:(Context.to_build_context t.context)
+    ~context:(Context.build_context t.context)
     ~env alias ~loc ?locks ~stamp action
 
 let build_dir_is_vendored build_dir =