Remove env_extra in Action

It's simply to just use Env.t everywhere. Also, there's no need to have the env
in the execution context since it's not used for anything. Only the env that is
passed directly is used.

src/action.ml

@@ -697,10 +697,9 @@ end
 type exec_context =
   { context : Context.t option
   ; purpose : Process.purpose
-  ; env     : Env.t
   }
 
-let exec_run_direct ~ectx ~dir ~env_extra ~stdout_to ~stderr_to prog args =
+let exec_run_direct ~ectx ~dir ~env ~stdout_to ~stderr_to prog args =
   begin match ectx.context with
    | None
    | Some { Context.for_host = None; _ } -> ()
@@ -715,7 +714,6 @@ let exec_run_direct ~ectx ~dir ~env_extra ~stdout_to ~stderr_to prog args =
      invalid_prefix ("_build/" ^ target.name);
      invalid_prefix ("_build/install/" ^ target.name);
   end;
-  let env = Env.extend ectx.env ~vars:env_extra in
   Process.run Strict ~dir:(Path.to_string dir) ~env
     ~stdout_to ~stderr_to
     ~purpose:ectx.purpose
@@ -732,17 +730,17 @@ let exec_echo stdout_to str =
      | None -> print_string str; flush stdout
      | Some (_, oc) -> output_string oc str)
 
-let rec exec t ~ectx ~dir ~env_extra ~stdout_to ~stderr_to =
+let rec exec t ~ectx ~dir ~env ~stdout_to ~stderr_to =
   match t with
   | Run (Error e, _) ->
     Prog.Not_found.raise e
   | Run (Ok prog, args) ->
-    exec_run ~ectx ~dir ~env_extra ~stdout_to ~stderr_to prog args
+    exec_run ~ectx ~dir ~env ~stdout_to ~stderr_to prog args
   | Chdir (dir, t) ->
-    exec t ~ectx ~dir ~env_extra ~stdout_to ~stderr_to
+    exec t ~ectx ~dir ~env ~stdout_to ~stderr_to
   | Setenv (var, value, t) ->
     exec t ~ectx ~dir ~stdout_to ~stderr_to
-      ~env_extra:(Env.Map.add env_extra var value)
+      ~env:(Env.add env ~var ~value)
   | Redirect (Stdout, fn, Echo s) ->
     Io.write_file (Path.to_string fn) s;
     Fiber.return ()
@@ -754,13 +752,13 @@ let rec exec t ~ectx ~dir ~env_extra ~stdout_to ~stderr_to =
       | Stderr -> (get_std_output stdout_to, out)
       | Outputs -> (out, out)
     in
-    exec_run_direct ~ectx ~dir ~env_extra ~stdout_to ~stderr_to prog args
+    exec_run_direct ~ectx ~dir ~env ~stdout_to ~stderr_to prog args
   | Redirect (outputs, fn, t) ->
-    redirect ~ectx ~dir outputs fn t ~env_extra ~stdout_to ~stderr_to
+    redirect ~ectx ~dir outputs fn t ~env ~stdout_to ~stderr_to
   | Ignore (outputs, t) ->
-    redirect ~ectx ~dir outputs Config.dev_null t ~env_extra ~stdout_to ~stderr_to
+    redirect ~ectx ~dir outputs Config.dev_null t ~env ~stdout_to ~stderr_to
   | Progn l ->
-    exec_list l ~ectx ~dir ~env_extra ~stdout_to ~stderr_to
+    exec_list l ~ectx ~dir ~env ~stdout_to ~stderr_to
   | Echo str -> exec_echo stdout_to str
   | Cat fn ->
     Io.with_file_in (Path.to_string fn) ~f:(fun ic ->
@@ -813,9 +811,9 @@ let rec exec t ~ectx ~dir ~env_extra ~stdout_to ~stderr_to =
     let path, arg =
       Utils.system_shell_exn ~needed_to:"interpret (system ...) actions"
     in
-    exec_run ~ectx ~dir ~env_extra ~stdout_to ~stderr_to path [arg; cmd]
+    exec_run ~ectx ~dir ~env ~stdout_to ~stderr_to path [arg; cmd]
   | Bash cmd ->
-    exec_run ~ectx ~dir ~env_extra ~stdout_to ~stderr_to
+    exec_run ~ectx ~dir ~env ~stdout_to ~stderr_to
       (Utils.bash_exn ~needed_to:"interpret (bash ...) actions")
       ["-e"; "-u"; "-o"; "pipefail"; "-c"; cmd]
   | Write_file (fn, s) ->
@@ -867,7 +865,7 @@ let rec exec t ~ectx ~dir ~env_extra ~stdout_to ~stderr_to =
       Print_diff.print file1 file2
     end
 
-and redirect outputs fn t ~ectx ~dir ~env_extra ~stdout_to ~stderr_to =
+and redirect outputs fn t ~ectx ~dir ~env ~stdout_to ~stderr_to =
   let fn = Path.to_string fn in
   let oc = Io.open_out fn in
   let out = Some (fn, oc) in
@@ -877,18 +875,18 @@ and redirect outputs fn t ~ectx ~dir ~env_extra ~stdout_to ~stderr_to =
     | Stderr -> (stdout_to, out)
     | Outputs -> (out, out)
   in
-  exec t ~ectx ~dir ~env_extra ~stdout_to ~stderr_to >>| fun () ->
+  exec t ~ectx ~dir ~env ~stdout_to ~stderr_to >>| fun () ->
   close_out oc
 
-and exec_list l ~ectx ~dir ~env_extra ~stdout_to ~stderr_to =
+and exec_list l ~ectx ~dir ~env ~stdout_to ~stderr_to =
   match l with
   | [] ->
     Fiber.return ()
   | [t] ->
-    exec t ~ectx ~dir ~env_extra ~stdout_to ~stderr_to
+    exec t ~ectx ~dir ~env ~stdout_to ~stderr_to
   | t :: rest ->
-    exec t ~ectx ~dir ~env_extra ~stdout_to ~stderr_to >>= fun () ->
-    exec_list rest ~ectx ~dir ~env_extra ~stdout_to ~stderr_to
+    exec t ~ectx ~dir ~env ~stdout_to ~stderr_to >>= fun () ->
+    exec_list rest ~ectx ~dir ~env ~stdout_to ~stderr_to
 
 let exec ~targets ?context t =
   let env =
@@ -898,9 +896,8 @@ let exec ~targets ?context t =
   in
   let targets = Path.Set.to_list targets in
   let purpose = Process.Build_job targets in
-  let ectx = { purpose; context; env } in
-  exec t ~ectx ~dir:Path.root ~env_extra:Env.Map.empty
-    ~stdout_to:None ~stderr_to:None
+  let ectx = { purpose; context } in
+  exec t ~ectx ~dir:Path.root ~env ~stdout_to:None ~stderr_to:None
 
 let sandbox t ~sandboxed ~deps ~targets =
   Progn