diff --git a/src/action.ml b/src/action.ml
index c622c675..aefaac06 100644
--- a/src/action.ml
+++ b/src/action.ml
@@ -1,8 +1,105 @@
-type t =
-  { prog      : Path.t
-  ; args      : string list
-  ; dir       : Path.t
-  ; env       : string array
-  ; stdout_to : Path.t option
-  ; touches   : Path.t list
-  }
+open Import
+open Sexp.Of_sexp
+
+module Mini_shexp = struct
+  type 'a t =
+    | Run            of 'a * 'a list
+    | Chdir          of 'a * 'a t
+    | Setenv         of 'a * 'a * 'a t
+    | With_stdout_to of 'a * 'a t
+
+  let rec t a sexp =
+    sum
+      [ cstr_rest "run" (a @> nil) a             (fun prog args -> Run (prog, args))
+      ; cstr "chdir"    (a @> t a @> nil)        (fun dn t -> Chdir (dn, t))
+      ; cstr "setenv"   (a @> a @> t a @> nil)   (fun k v t -> Setenv (k, v, t))
+      ; cstr "with-stdout-to" (a @> t a @> nil)  (fun fn t -> With_stdout_to (fn, t))
+      ]
+      sexp
+
+  let rec map t ~f =
+    match t with
+    | Run (prog, args) -> Run (f prog, List.map args ~f)
+    | Chdir (fn, t) -> Chdir (f fn, map t ~f)
+    | Setenv (var, value, t) -> Setenv (f var, f value, map t ~f)
+    | With_stdout_to (fn, t) -> With_stdout_to (f fn, map t ~f)
+
+  let rec fold t ~init:acc ~f =
+    match t with
+    | Run (prog, args) -> List.fold_left args ~init:(f acc prog) ~f
+    | Chdir (fn, t) -> fold t ~init:(f acc fn) ~f
+    | Setenv (var, value, t) -> fold t ~init:(f (f acc var) value) ~f
+    | With_stdout_to (fn, t) -> fold t ~init:(f acc fn) ~f
+
+  let to_action ~dir ~env (t : string t) =
+    let rec loop vars dir stdouts = function
+      | Chdir (fn, t) ->
+        loop vars (Path.relative dir fn) stdouts t
+      | Setenv (var, value, t) ->
+        loop (String_map.add vars ~key:var ~data:value) dir stdouts t
+      | With_stdout_to (fn, t) ->
+        loop vars dir (Path.relative dir fn :: stdouts) t
+      | Run (prog, args) ->
+        let stdout_to, touches =
+          match stdouts with
+          | [] -> None, []
+          | p :: rest -> (Some p, rest)
+        in
+        { Action.
+          prog = Path.relative dir prog
+        ; args = args
+        ; dir
+        ; env = Context.extend_env ~vars ~env
+        ; stdout_to
+        ; touches
+        }
+    in
+    loop String_map.empty dir [] t
+
+  let rec sexp_of_t f : _ -> Sexp.t = function
+    | Run (a, xs) -> List (Atom "run" :: f a :: List.map xs ~f)
+    | Chdir (a, r) -> List [Atom "chdir" ; f a ; sexp_of_t f r]
+    | Setenv (k, v, r) -> List [Atom "setenv" ; f k ; f v ; sexp_of_t f r]
+    | With_stdout_to (fn, r) -> List [Atom "with-stdout-to"; f fn; sexp_of_t f r]
+end
+
+module T = struct
+  type 'a t =
+    | Bash of 'a
+    | Shexp of 'a Mini_shexp.t
+
+  let t a sexp =
+    match sexp with
+    | Atom _ -> Bash  (a              sexp)
+    | List _ -> Shexp (Mini_shexp.t a sexp)
+
+  let map t ~f =
+    match t with
+    | Bash x -> Bash (f x)
+    | Shexp x -> Shexp (Mini_shexp.map x ~f)
+
+  let fold t ~init ~f =
+    match t with
+    | Bash x -> f init x
+    | Shexp x -> Mini_shexp.fold x ~init ~f
+
+  let sexp_of_t f : _ -> Sexp.t = function
+    | Bash a -> List [Atom "bash" ; f a]
+    | Shexp a -> List [Atom "shexp" ; Mini_shexp.sexp_of_t f a]
+end
+
+include T
+
+module Unexpanded = String_with_vars.Lift(T)
+
+let to_action ~dir ~env = function
+  | Shexp shexp -> Mini_shexp.to_action ~dir ~env shexp
+  | Bash cmd ->
+    { Action.
+      prog = Path.absolute "/bin/bash"
+    ; args = ["-e"; "-u"; "-o"; "pipefail"; "-c"; cmd]
+    ; env
+    ; dir
+    ; stdout_to = None
+    ; touches = []
+    }
diff --git a/src/build.mli b/src/build.mli
index 464e9b6a..d2491db2 100644
--- a/src/build.mli
+++ b/src/build.mli
@@ -78,7 +78,11 @@ val run_capture_lines
   -> 'a Arg_spec.t list
   -> ('a, string list) t
 
-val action : targets:Path.t list -> (Action.t, unit) t
+val action
+  :  dir:Path.t
+  -> env:string array
+  -> targets:Path.t list
+  -> (string Action.t, unit) t
 
 (** Create a file with the given contents. *)
 val echo : Path.t -> (string, unit) t
diff --git a/src/jbuild_types.ml b/src/jbuild_types.ml
index cf6242b3..4ab6634c 100644
--- a/src/jbuild_types.ml
+++ b/src/jbuild_types.ml
@@ -117,111 +117,6 @@ module Pp_or_flag = struct
       | Flag s -> Inr s)
 end
 
-module User_action = struct
-  module Mini_shexp = struct
-    type 'a t =
-      | Run    of 'a * 'a list
-      | Chdir  of 'a * 'a t
-      | Setenv of 'a * 'a * 'a t
-      | With_stdout_to of 'a * 'a t
-
-    let rec t a sexp =
-      sum
-        [ cstr_rest "run" (a @> nil) a             (fun prog args -> Run (prog, args))
-        ; cstr "chdir"    (a @> t a @> nil)        (fun dn t -> Chdir (dn, t))
-        ; cstr "setenv"   (a @> a @> t a @> nil)   (fun k v t -> Setenv (k, v, t))
-        ; cstr "with-stdout-to" (a @> t a @> nil)  (fun fn t -> With_stdout_to (fn, t))
-        ]
-        sexp
-
-    let rec map t ~f =
-      match t with
-      | Run (prog, args) -> Run (f prog, List.map args ~f)
-      | Chdir (fn, t) -> Chdir (f fn, map t ~f)
-      | Setenv (var, value, t) -> Setenv (f var, f value, map t ~f)
-      | With_stdout_to (fn, t) -> With_stdout_to (f fn, map t ~f)
-
-    let rec fold t ~init:acc ~f =
-      match t with
-      | Run (prog, args) -> List.fold_left args ~init:(f acc prog) ~f
-      | Chdir (fn, t) -> fold t ~init:(f acc fn) ~f
-      | Setenv (var, value, t) -> fold t ~init:(f (f acc var) value) ~f
-      | With_stdout_to (fn, t) -> fold t ~init:(f acc fn) ~f
-
-    let to_action ~dir ~env (t : string t) =
-      let rec loop vars dir stdouts = function
-        | Chdir (fn, t) ->
-          loop vars (Path.relative dir fn) stdouts t
-        | Setenv (var, value, t) ->
-          loop (String_map.add vars ~key:var ~data:value) dir stdouts t
-        | With_stdout_to (fn, t) ->
-          loop vars dir (Path.relative dir fn :: stdouts) t
-        | Run (prog, args) ->
-          let stdout_to, touches =
-            match stdouts with
-            | [] -> None, []
-            | p :: rest -> (Some p, rest)
-          in
-          { Action.
-            prog = Path.relative dir prog
-          ; args = args
-          ; dir
-          ; env = Context.extend_env ~vars ~env
-          ; stdout_to
-          ; touches
-          }
-      in
-      loop String_map.empty dir [] t
-
-    let rec sexp_of_t f : _ -> Sexp.t = function
-      | Run (a, xs) -> List (Atom "run" :: f a :: List.map xs ~f)
-      | Chdir (a, r) -> List [Atom "chdir" ; f a ; sexp_of_t f r]
-      | Setenv (k, v, r) -> List [Atom "setenv" ; f k ; f v ; sexp_of_t f r]
-      | With_stdout_to (fn, r) -> List [Atom "with-stdout-to"; f fn; sexp_of_t f r]
-  end
-
-  module T = struct
-    type 'a t =
-      | Bash of 'a
-      | Shexp of 'a Mini_shexp.t
-
-    let t a sexp =
-      match sexp with
-      | Atom _ -> Bash  (a              sexp)
-      | List _ -> Shexp (Mini_shexp.t a sexp)
-
-    let map t ~f =
-      match t with
-      | Bash x -> Bash (f x)
-      | Shexp x -> Shexp (Mini_shexp.map x ~f)
-
-    let fold t ~init ~f =
-      match t with
-      | Bash x -> f init x
-      | Shexp x -> Mini_shexp.fold x ~init ~f
-
-    let sexp_of_t f : _ -> Sexp.t = function
-      | Bash a -> List [Atom "bash" ; f a]
-      | Shexp a -> List [Atom "shexp" ; Mini_shexp.sexp_of_t f a]
-  end
-
-  include T
-
-  module Unexpanded = String_with_vars.Lift(T)
-
-  let to_action ~dir ~env = function
-    | Shexp shexp -> Mini_shexp.to_action ~dir ~env shexp
-    | Bash cmd ->
-      { Action.
-        prog = Path.absolute "/bin/bash"
-      ; args = ["-e"; "-u"; "-o"; "pipefail"; "-c"; cmd]
-      ; env
-      ; dir
-      ; stdout_to = None
-      ; touches = []
-      }
-end
-
 module Dep_conf = struct
   type t =
     | File of String_with_vars.t
@@ -653,13 +548,13 @@ module Rule = struct
   type t =
     { targets : string list (** List of files in the current directory *)
     ; deps    : Dep_conf.t list
-    ; action  : User_action.Unexpanded.t
+    ; action  : Action.Unexpanded.t
     }
 
   let common =
     field "targets" (list file_in_current_dir)    >>= fun targets ->
     field "deps"    (list Dep_conf.t) ~default:[] >>= fun deps ->
-    field "action"  User_action.Unexpanded.t      >>= fun action ->
+    field "action"  Action.Unexpanded.t           >>= fun action ->
     return { targets; deps; action }
 
   let v1 = record common
@@ -748,13 +643,13 @@ module Alias_conf = struct
   type t =
     { name  : string
     ; deps  : Dep_conf.t list
-    ; action : User_action.Unexpanded.t option
+    ; action : Action.Unexpanded.t option
     }
 
   let common =
     field "name" string                        >>= fun name ->
     field "deps" (list Dep_conf.t) ~default:[] >>= fun deps ->
-    field_o "action" User_action.Unexpanded.t  >>= fun action ->
+    field_o "action" Action.Unexpanded.t  >>= fun action ->
     return
       { name
       ; deps