Generalize expansion to be in own module

The result is Super_context.Expander which can be used for expandding OSL as well

Signed-off-by: Rudi Grinberg <rudi.grinberg@gmail.com>

src/super_context.ml

@@ -560,15 +560,44 @@ module Scope_key = struct
     sprintf "%s@%s" key (Dune_project.Name.encode scope)
 end
 
-module Action = struct
-  open Build.O
-  module U = Action.Unexpanded
-
 type targets =
   | Static of Path.t list
   | Infer
   | Alias
 
+module Expander : sig
+  module Resolved_forms : sig
+    type t
+
+    (* Failed resolutions *)
+    val failures : t -> fail list
+
+    (* All "name" for %{lib:name:...}/%{lib-available:name} forms *)
+    val lib_deps : t -> Build.lib_deps
+
+    (* Static deps from %{...} variables. For instance %{exe:...} *)
+    val sdeps    : t -> Path.Set.t
+
+    (* Dynamic deps from %{...} variables. For instance %{read:...} *)
+    val ddeps    : t -> (unit, Value.t list) Build.t String.Map.t
+  end
+
+  type sctx = t
+
+  type expander
+    =  sctx
+    -> dir:Path.t
+    -> dep_kind:Build.lib_dep_kind
+    -> scope:Scope.t
+    -> targets_written_by_user:targets
+    -> map_exe:(Path.t -> Path.t)
+    -> bindings:Pform.Map.t
+    -> String_with_vars.Var.t
+    -> Syntax.Version.t
+    -> Value.t list option
+
+  val with_expander : (expander -> 'a) -> 'a * Resolved_forms.t
+end = struct
   module Resolved_forms = struct
     type t =
       { (* Failed resolutions *)
@@ -581,6 +610,11 @@ module Action = struct
         mutable ddeps     : (unit, Value.t list) Build.t String.Map.t
       }
 
+    let failures t = t.failures
+    let lib_deps t = t.lib_deps
+    let sdeps t = t.sdeps
+    let ddeps t = t.ddeps
+
     let empty () =
       { failures  = []
       ; lib_deps  = String.Map.empty
@@ -600,29 +634,33 @@ module Action = struct
       None
   end
 
+  type sctx = t
+
+  type expander
+    =  sctx
+    -> dir:Path.t
+    -> dep_kind:Build.lib_dep_kind
+    -> scope:Scope.t
+    -> targets_written_by_user:targets
+    -> map_exe:(Path.t -> Path.t)
+    -> bindings:Pform.Map.t
+    -> String_with_vars.Var.t
+    -> Syntax.Version.t
+    -> Value.t list option
+
   let path_exp path = [Value.Path path]
   let str_exp  str  = [Value.String str]
 
-  let map_exe sctx =
-    match sctx.host with
-    | None -> (fun exe -> exe)
-    | Some host ->
-      fun exe ->
-        match Path.extract_build_context_dir exe with
-        | Some (dir, exe) when dir = sctx.context.build_dir ->
-          Path.append host.context.build_dir exe
-        | _ -> exe
-
   let parse_lib_file ~loc s =
     match String.lsplit2 s ~on:':' with
     | None ->
       Loc.fail loc "invalid %%{lib:...} form: %s" s
     | Some x -> x
 
-  let expand_step1 sctx ~dir ~dep_kind ~scope ~targets_written_by_user
-        ~map_exe ~bindings t =
-    let acc = Resolved_forms.empty () in
-    let expand pform syntax_version =
+  open Build.O
+
+  let expander ~acc sctx ~dir ~dep_kind ~scope ~targets_written_by_user
+        ~map_exe ~bindings pform syntax_version =
     let loc = String_with_vars.Var.loc pform in
     let key = String_with_vars.Var.full_name pform in
     let res =
@@ -738,9 +776,40 @@ module Action = struct
                      (Path.Set.of_list (Value.L.deps_only v)) acc.sdeps
     );
     res
-    in
-    let t = U.partial_expand t ~dir ~map_exe ~f:expand in
-    (t, acc)
+
+  let with_expander
+    : 'a. (expander -> 'a) -> 'a * Resolved_forms.t
+    = fun f ->
+      let acc = Resolved_forms.empty () in
+      (f (expander ~acc), acc)
+end
+
+module Action = struct
+  open Build.O
+  module U = Action.Unexpanded
+
+  type nonrec targets = targets =
+    | Static of Path.t list
+    | Infer
+    | Alias
+
+
+  let map_exe sctx =
+    match sctx.host with
+    | None -> (fun exe -> exe)
+    | Some host ->
+      fun exe ->
+        match Path.extract_build_context_dir exe with
+        | Some (dir, exe) when dir = sctx.context.build_dir ->
+          Path.append host.context.build_dir exe
+        | _ -> exe
+
+  let expand_step1 sctx ~dir ~dep_kind ~scope ~targets_written_by_user
+        ~map_exe ~bindings t =
+    Expander.with_expander (fun expander ->
+      let f = expander sctx ~dir ~dep_kind ~scope ~targets_written_by_user
+                ~map_exe ~bindings in
+      U.partial_expand t ~dir ~map_exe ~f)
 
   let expand_step2 ~dir ~dynamic_expansions ~bindings
         ~(deps_written_by_user : Path.t Jbuild.Bindings.t)
@@ -826,13 +895,13 @@ module Action = struct
              sprintf "- %s" (Utils.describe_target target))
            |> String.concat ~sep:"\n"));
     let build =
-      Build.record_lib_deps_simple forms.lib_deps
+      Build.record_lib_deps_simple (Expander.Resolved_forms.lib_deps forms)
       >>>
-      Build.path_set (Path.Set.union deps forms.sdeps)
+      Build.path_set (Path.Set.union deps (Expander.Resolved_forms.sdeps forms))
       >>>
       Build.arr (fun paths -> ((), paths))
       >>>
-      let ddeps = String.Map.to_list forms.ddeps in
+      let ddeps = String.Map.to_list (Expander.Resolved_forms.ddeps forms) in
       Build.first (Build.all (List.map ddeps ~f:snd))
       >>^ (fun (vals, deps_written_by_user) ->
         let dynamic_expansions =
@@ -857,7 +926,7 @@ module Action = struct
       >>>
       Build.action_dyn () ~dir ~targets
     in
-    match forms.failures with
+    match Expander.Resolved_forms.failures forms with
     | [] -> build
     | fail :: _ -> Build.fail fail >>> build
 end