feature: remove limitations on [enabled_if] on libraries

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

<!-- ps-id: 2eb4a6ec-7903-421c-a370-9bbc0136e47a -->

doc/changes/10250.md

@@ -0,0 +1,2 @@
+- Remove limitations on percent forms in the `(enabled_if ..)` field of
+  libraries (#10250, @rgrinberg)

src/dune_rules/artifacts_obj.ml

@@ -10,12 +10,14 @@ let empty = { libraries = Lib_name.Map.empty; modules = Module_name.Map.empty }
 let lookup_module { modules; libraries = _ } = Module_name.Map.find modules
 let lookup_library { libraries; modules = _ } = Lib_name.Map.find libraries
 
-let make ~dir ~lib_config ~libs ~exes =
+let make ~dir ~expander ~lib_config ~libs ~exes =
   let+ libraries =
     Memo.List.map libs ~f:(fun ((lib : Library.t), _, _, _) ->
       let+ lib_config = lib_config in
       let name = Lib_name.of_local lib.name in
-      let info = Library.to_lib_info lib ~dir ~lib_config in
+      let info =
+        Library.to_lib_info lib ~expander:(Memo.return expander) ~dir ~lib_config
+      in
       name, info)
     >>| Lib_name.Map.of_list_exn
   in

src/dune_rules/artifacts_obj.mli

@@ -6,6 +6,7 @@ val empty : t
 
 val make
   :  dir:Path.Build.t
+  -> expander:Expander0.t
   -> lib_config:Lib_config.t Memo.t
   -> libs:(Library.t * _ * Modules.t * Path.Build.t Obj_dir.t) list
   -> exes:(_ * _ * Modules.t * Path.Build.t Obj_dir.t) list

src/dune_rules/expander.ml

@@ -63,6 +63,7 @@ type t =
 
 let artifacts t = t.artifacts_host
 let dir t = t.dir
+let project t = t.project
 let context t = Context.name t.context
 
 let set_local_env_var t ~var ~value =
@@ -909,3 +910,12 @@ let expand_locks t (locks : Locks.t) =
   Memo.List.map locks ~f:(fun (Lock x) -> No_deps.expand_path t x)
   |> Action_builder.of_memo
 ;;
+
+module M = struct
+  type nonrec t = t
+
+  let project = project
+  let eval_blang = eval_blang
+end
+
+let to_expander0 t = Expander0.create (Memo.return t) (module M)

src/dune_rules/expander.mli

@@ -6,6 +6,7 @@ type t
 
 val dir : t -> Path.Build.t
 val context : t -> Context_name.t
+val project : t -> Dune_project.t
 
 val make_root
   :  project:Dune_project.t
@@ -123,3 +124,4 @@ val foreign_flags
       Fdecl.t
 
 val lookup_artifacts : (dir:Path.Build.t -> Artifacts_obj.t Memo.t) Fdecl.t
+val to_expander0 : t -> Expander0.t

src/dune_rules/expander0.ml

@@ -24,3 +24,26 @@ let as_in_build_dir ~what ~loc p =
           (Path.to_string_maybe_quoted p)
       ]
 ;;
+
+module type S = sig
+  type t
+
+  val project : t -> Dune_project.t
+  val eval_blang : t -> Blang.t -> bool Memo.t
+end
+
+open Memo.O
+
+type t = E : 'a Memo.t * (module S with type t = 'a) -> t
+
+let db = Fdecl.create Dyn.opaque
+let set_db = Fdecl.set db
+let create e m = E (e, m)
+let project (E (e, (module E))) = Memo.map e ~f:E.project
+
+let eval_blang (E (e, (module E))) blang =
+  let* e = e in
+  E.eval_blang e blang
+;;
+
+let get ~dir = (Fdecl.get db) ~dir

src/dune_rules/expander0.mli

@@ -2,3 +2,17 @@ open Import
 
 val isn't_allowed_in_this_position : source:Dune_lang.Template.Pform.t -> 'a
 val as_in_build_dir : what:string -> loc:Loc.t -> Path.t -> Path.Build.t
+
+module type S = sig
+  type t
+
+  val project : t -> Dune_project.t
+  val eval_blang : t -> Blang.t -> bool Memo.t
+end
+
+include S
+
+val set_db : (dir:Path.Build.t -> t Memo.t) -> unit
+val get : dir:Path.Build.t -> t Memo.t
+val project : t -> Dune_project.t Memo.t
+val create : 'a Memo.t -> (module S with type t = 'a) -> t

src/dune_rules/install_rules.ml

@@ -170,7 +170,14 @@ end = struct
       ocaml.lib_config
     in
     let make_entry ?(loc = loc) = make_entry lib_subdir ~loc in
-    let info = Library.to_lib_info lib ~dir ~lib_config in
+    let* expander = Super_context.expander sctx ~dir in
+    let info =
+      Library.to_lib_info
+        lib
+        ~expander:(Memo.return (Expander.to_expander0 expander))
+        ~dir
+        ~lib_config
+    in
     let lib_name = Library.best_name lib in
     let* installable_modules =
       let+ modules =
@@ -210,26 +217,24 @@ end = struct
           in
           make_entry ?sub_dir Lib source ?dst))
     in
-    let* additional_deps =
-      let+ expander = Super_context.expander sctx ~dir:lib_src_dir in
-      fun (loc, deps) ->
-        Lib_file_deps.eval deps ~expander ~loc ~paths:(Disallow_external lib_name)
-        >>| Path.Set.to_list_map ~f:(fun path ->
-          let path =
-            let path = path |> Path.as_in_build_dir_exn in
-            check_runtime_deps_relative_path ~lib_info:info ~loc (Path.Build.local path);
-            path
-          in
-          let sub_dir =
-            let src_dir = Path.Build.parent_exn path in
-            match Path.Build.equal lib_src_dir src_dir with
-            | true -> None
-            | false ->
-              Path.Build.local src_dir
-              |> Path.Local.descendant ~of_:(Path.Build.local lib_src_dir)
-              |> Option.map ~f:Path.Local.to_string
-          in
-          make_entry ?sub_dir Lib path)
+    let additional_deps (loc, deps) =
+      Lib_file_deps.eval deps ~expander ~loc ~paths:(Disallow_external lib_name)
+      >>| Path.Set.to_list_map ~f:(fun path ->
+        let path =
+          let path = path |> Path.as_in_build_dir_exn in
+          check_runtime_deps_relative_path ~lib_info:info ~loc (Path.Build.local path);
+          path
+        in
+        let sub_dir =
+          let src_dir = Path.Build.parent_exn path in
+          match Path.Build.equal lib_src_dir src_dir with
+          | true -> None
+          | false ->
+            Path.Build.local src_dir
+            |> Path.Local.descendant ~of_:(Path.Build.local lib_src_dir)
+            |> Option.map ~f:Path.Local.to_string
+        in
+        make_entry ?sub_dir Lib path)
     in
     let { Lib_config.has_native; ext_obj; _ } = lib_config in
     let { Lib_mode.Map.ocaml = { Mode.Dict.byte; native } as ocaml; melange } =

src/dune_rules/lib_rules.ml

@@ -580,13 +580,19 @@ let library_rules
   let* () =
     Memo.Option.iter vimpl ~f:(Virtual_rules.setup_copy_rules_for_impl ~sctx ~dir)
   in
+  let* expander = Super_context.expander sctx ~dir in
   let* () = Check_rules.add_cycle_check sctx ~dir top_sorted_modules in
   let* () = gen_wrapped_compat_modules lib cctx
   and* () = Module_compilation.build_all cctx
-  and* expander = Super_context.expander sctx ~dir
   and* lib_info =
     let lib_config = ocaml.lib_config in
-    let info = Library.to_lib_info lib ~dir ~lib_config in
+    let info =
+      Library.to_lib_info
+        lib
+        ~expander:(Memo.return (Expander.to_expander0 expander))
+        ~dir
+        ~lib_config
+    in
     let mode = Lib_mode.Map.Set.for_merlin (Lib_info.modes info) in
     let+ () = Check_rules.add_obj_dir sctx ~obj_dir mode in
     info

src/dune_rules/ml_sources.ml

@@ -547,6 +547,7 @@ let make
     Memo.lazy_ (fun () ->
       Artifacts_obj.make
         ~dir
+        ~expander:(Expander.to_expander0 expander)
         ~lib_config
         ~libs:modules_of_stanzas.libraries
         ~exes:modules_of_stanzas.executables)

src/dune_rules/scope.ml

@@ -52,7 +52,7 @@ module DB = struct
   end
 
   let create_db_from_stanzas ~instrument_with ~parent ~lib_config stanzas =
-    let (map : Found_or_redirect.t Lib_name.Map.t) =
+    let map =
       List.map stanzas ~f:(fun stanza ->
         match (stanza : Library_related_stanza.t) with
         | Library_redirect s ->
@@ -62,7 +62,10 @@ module DB = struct
           let old_public_name = Deprecated_library_name.old_public_name s in
           Found_or_redirect.redirect old_public_name s.new_public_name
         | Library (dir, (conf : Library.t)) ->
-          let info = Library.to_lib_info conf ~dir ~lib_config |> Lib_info.of_local in
+          let info =
+            let expander = Expander0.get ~dir in
+            Library.to_lib_info conf ~expander ~dir ~lib_config |> Lib_info.of_local
+          in
           Library.best_name conf, Found_or_redirect.found info)
       |> Lib_name.Map.of_list_reducei ~f:(fun name (v1 : Found_or_redirect.t) v2 ->
         let res =
@@ -100,11 +103,12 @@ module DB = struct
       ~parent:(Some parent)
       ~resolve:(fun name ->
         Memo.return
-          (match Lib_name.Map.find map name with
-           | None -> Lib.DB.Resolve_result.not_found
-           | Some (Redirect lib) -> Lib.DB.Resolve_result.redirect_in_the_same_db lib
-           | Some (Found lib) -> Lib.DB.Resolve_result.found lib))
-      ~all:(fun () -> Lib_name.Map.keys map |> Memo.return)
+        @@
+        match Lib_name.Map.find map name with
+        | None -> Lib.DB.Resolve_result.not_found
+        | Some (Redirect lib) -> Lib.DB.Resolve_result.redirect_in_the_same_db lib
+        | Some (Found lib) -> Lib.DB.Resolve_result.found lib)
+      ~all:(fun () -> Memo.return @@ Lib_name.Map.keys map)
       ~lib_config
       ~instrument_with
   ;;

src/dune_rules/stanzas/library.ml

@@ -166,10 +166,13 @@ let decode =
      and+ enabled_if =
        let open Enabled_if in
        let allowed_vars =
-         Only
-           (("context_name", (2, 8))
-            :: ("profile", (2, 5))
-            :: Lib_config.allowed_in_enabled_if)
+         if Dune_project.dune_version project >= (3, 15)
+         then Any
+         else
+           Only
+             (("context_name", (2, 8))
+              :: ("profile", (2, 5))
+              :: Lib_config.allowed_in_enabled_if)
        in
        decode ~allowed_vars ~since:(Some (1, 10)) ()
      and+ instrumentation_backend =
@@ -402,6 +405,7 @@ let main_module_name t : Lib_info.Main_module_name.t =
 
 let to_lib_info
   conf
+  ~expander
   ~dir
   ~lib_config:
     ({ Lib_config.has_native; ext_lib; ext_dll; natdynlink_supported; _ } as lib_config)
@@ -474,19 +478,24 @@ let to_lib_info
   let name = best_name conf in
   let enabled =
     let+ enabled_if_result =
-      Blang_expand.eval conf.enabled_if ~dir:(Path.build dir) ~f:(fun ~source:_ pform ->
-        let+ value =
-          match pform with
-          | Var Context_name ->
-            let context, _ = Path.Build.extract_build_context_exn dir in
-            Memo.return context
-          | Var Profile ->
-            let context, _ = Path.Build.extract_build_context_exn dir in
-            let+ profile = Per_context.profile (Context_name.of_string context) in
-            Profile.to_string profile
-          | _ -> Memo.return @@ Lib_config.get_for_enabled_if lib_config pform
-        in
-        [ Value.String value ])
+      let* expander = expander in
+      let* project = Expander0.project expander in
+      if Dune_project.dune_version project >= (3, 15)
+      then Expander0.eval_blang expander conf.enabled_if
+      else
+        Blang_expand.eval conf.enabled_if ~dir:(Path.build dir) ~f:(fun ~source:_ pform ->
+          let+ value =
+            match pform with
+            | Var Context_name ->
+              let context, _ = Path.Build.extract_build_context_exn dir in
+              Memo.return context
+            | Var Profile ->
+              let context, _ = Path.Build.extract_build_context_exn dir in
+              let+ profile = Per_context.profile (Context_name.of_string context) in
+              Profile.to_string profile
+            | _ -> Memo.return @@ Lib_config.get_for_enabled_if lib_config pform
+          in
+          [ Value.String value ])
     in
     if not enabled_if_result
     then Lib_info.Enabled_status.Disabled_because_of_enabled_if

src/dune_rules/stanzas/library.mli

@@ -76,4 +76,10 @@ val is_virtual : t -> bool
 val is_impl : t -> bool
 val obj_dir : dir:Path.Build.t -> t -> Path.Build.t Obj_dir.t
 val main_module_name : t -> Lib_info.Main_module_name.t
-val to_lib_info : t -> dir:Path.Build.t -> lib_config:Lib_config.t -> Lib_info.local
+
+val to_lib_info
+  :  t
+  -> expander:Expander0.t Memo.t
+  -> dir:Path.Build.t
+  -> lib_config:Lib_config.t
+  -> Lib_info.local

src/dune_rules/super_context.ml

@@ -382,7 +382,13 @@ let () =
     let* ctx = Context.DB.by_dir dir in
     let* t = find_exn (Context.name ctx) in
     let* expander = expander t ~dir in
-    Expander.expand_str expander sw |> Action_builder.evaluate_and_collect_facts >>| fst)
+    Expander.expand_str expander sw |> Action_builder.evaluate_and_collect_facts >>| fst);
+  Expander0.set_db (fun ~dir ->
+    Context.DB.by_dir dir
+    >>| Context.name
+    >>= find_exn
+    >>= expander ~dir
+    >>| Expander.to_expander0)
 ;;
 
 let context t = t.context

test/blackbox-tests/test-cases/enabled_if/eif-library-name-collision.t

@@ -40,6 +40,7 @@ For private libraries
   Error: Library foo is defined twice:
   - a/dune:1
   - b/dune:1
+  -> required by alias default
   [1]
 
 For public libraries

test/blackbox-tests/test-cases/enabled_if/enabled-if-lib-other-vars.t

@@ -0,0 +1,16 @@
+Here we demonstrate that we expand any variable in enabled_if on libraries
+
+  $ cat >dune-project <<EOF
+  > (lang dune 3.15)
+  > EOF
+
+  $ cat >dune <<EOF
+  > (library
+  >  (name foo)
+  >  (enabled_if %{env:FOO=false}))
+  > EOF
+  $ dune build %{cma:./foo}
+  Error: No rule found for foo.cma
+  -> required by %{cma:./foo} at command line:1
+  [1]
+  $ FOO=true dune build %{cma:./foo}