Add simplified version of rules

src/gen_rules.ml

@@ -474,6 +474,10 @@ module Gen(P : Params) = struct
      | User rules                                                      |
      +-----------------------------------------------------------------+ *)
 
+  let do_rule (conf : Do.t) ~dir =
+    SC.add_rule sctx
+      (SC.Do_action.run sctx conf.action ~dir)
+
   let user_rule (rule : Rule.t) ~dir ~package_context =
     let targets = List.map rule.targets ~f:(Path.relative dir) in
     SC.add_rule sctx
@@ -600,6 +604,7 @@ module Gen(P : Params) = struct
       let dir = ctx_dir in
       match (stanza : Stanza.t) with
       | Rule         rule  -> user_rule   rule  ~dir ~package_context
+      | Do           conf  -> do_rule     conf  ~dir
       | Alias        alias -> alias_rules alias ~dir ~package_context
       | Library _ | Executables _ | Provides _ | Install _ -> ());
     let files = lazy (

src/jbuild_types.ml

@@ -727,6 +727,18 @@ module Rule = struct
       })
 end
 
+module Do = struct
+  type t =
+    { loc    : Loc.t
+    ; action : Action.Unexpanded.t
+    }
+
+  let v1 sexp =
+    { loc = Sexp.Ast.loc sexp
+    ; action = Action.Unexpanded.t sexp
+    }
+end
+
 module Menhir = struct
   type t =
     { base : string option
@@ -830,6 +842,7 @@ module Stanza = struct
     | Library     of Library.t
     | Executables of Executables.t
     | Rule        of Rule.t
+    | Do          of Do.t
     | Provides    of Provides.t
     | Install     of Install_conf.t
     | Alias       of Alias_conf.t
@@ -852,6 +865,7 @@ module Stanza = struct
       ; cstr "menhir"      (Menhir.v1 @> nil)            (fun x -> rules (Menhir.v1_to_rule x))
       ; cstr "install"     (Install_conf.v1 pkgs @> nil) (fun x -> [Install     x])
       ; cstr "alias"       (Alias_conf.v1 pkgs @> nil)   (fun x -> [Alias       x])
+      ; cstr "do"          (Do.v1 @> nil)                (fun x -> [Do          x])
       (* Just for validation and error messages *)
       ; cstr "jbuild_version" (Jbuild_version.t @> nil) (fun _ -> [])
       ]

src/super_context.ml

@@ -452,6 +452,25 @@ module Pkg_version = struct
     Build.vpath spec
 end
 
+module Do_action = struct
+  open Build.O
+  module U = Action.Unexpanded
+
+  let run t action ~dir =
+    let action =
+      Action.Unexpanded.expand t.context dir action ~f:(function
+        | "ROOT" -> Path t.context.build_dir
+        | var ->
+          match expand_var_no_root t var with
+          | Some s -> Str s
+          | None -> Not_found)
+    in
+    let { Action.Infer.Outcome.deps; targets } = Action.Infer.infer action in
+    Build.path_set deps
+    >>>
+    Build.action ~dir ~targets:(Path.Set.elements targets) action
+end
+
 module Action = struct
   open Build.O
   module U = Action.Unexpanded

src/super_context.mli

@@ -122,6 +122,15 @@ module Deps : sig
   val only_plain_files : t -> dir:Path.t -> Dep_conf.t list -> Path.t option list
 end
 
+(** Interpret "do" actions, for which targes are inferred *)
+module Do_action : sig
+  val run
+    :  t
+    -> Action.Unexpanded.t
+    -> dir:Path.t
+    -> (unit, Action.t) Build.t
+end
+
 (** Interpret action written in jbuild files *)
 module Action : sig
   val run