feature: [enabled_if] on packages

Add [enabled_if] when defining packages. This construct is limited to
the variables we can inspect using [Sys_poll]. The interpretation of
this field is the same including or excluding it from the set of visible
packages with --only-packages.

Signed-off-by: Rudi Grinberg <[email protected]>

Author: rgrinberg

bin/dune_init.ml

@@ -434,6 +434,7 @@ module Component = struct
                 }
               ]
             ~contents_basename:None
+            ~enabled_if:None
         in
         let packages = Package.Name.Map.singleton (Package.name package) package in
         let info =

doc/changes/added/12905.md

@@ -0,0 +1,4 @@
+- Add `enabled_if` on packages in `dune-project` files. If this field is set,
+  the expression is evaluated to determine whether to mask the package in this
+  workspace. When opam file generation is enabled, this field is converted to
+  a corresponding `available` expression (#12905, @rgrinbreg, @gridbugs)

src/dune_lang/package.ml

@@ -22,6 +22,7 @@ type t =
   ; depends : Package_dependency.t list
   ; conflicts : Package_dependency.t list
   ; depopts : Package_dependency.t list
+  ; enabled_if : Blang.t option
   ; info : Package_info.t
   ; version : Package_version.t option
   ; has_opam_file : opam_file
@@ -55,6 +56,7 @@ let original_opam_file t = t.original_opam_file
 let set_inside_opam_dir t ~dir = { t with opam_file = Name.file t.id.name ~dir }
 let set_version_and_info t ~version ~info = { t with version; info }
 let exclusive_dir t = t.exclusive_dir
+let enabled_if t = t.enabled_if
 
 let encode
       (name : Name.t)
@@ -75,6 +77,7 @@ let encode
       ; opam_file = _
       ; original_opam_file = _
       ; exclusive_dir
+      ; enabled_if
       }
   =
   let open Encoder in
@@ -87,6 +90,7 @@ let encode
         ; field_l "depends" Package_dependency.encode depends
         ; field_l "conflicts" Package_dependency.encode conflicts
         ; field_l "depopts" Package_dependency.encode depopts
+        ; field_o "enabled_if" Blang.encode enabled_if
         ; field_o "version" Package_version.encode version
         ; field "tags" (list string) ~default:[] tags
         ; field_l
@@ -109,6 +113,11 @@ let decode_name ~version =
 ;;
 
 let decode =
+  let enabled_if =
+    String_with_vars.set_decoding_env
+      Pform.Env.package_enabled_if
+      (Blang.Ast.decode ~override_decode_bare_literal:None String_with_vars.decode)
+  in
   let open Decoder in
   let name_map syntax of_list_map to_string name decode print_value error_msg =
     let+ names = field ~default:[] name (syntax >>> repeat decode) in
@@ -133,6 +142,9 @@ let decode =
        and+ depends = field ~default:[] "depends" (repeat Package_dependency.decode)
        and+ conflicts = field ~default:[] "conflicts" (repeat Package_dependency.decode)
        and+ depopts = field ~default:[] "depopts" (repeat Package_dependency.decode)
+       and+ enabled_if =
+         (* CR rgrinberg: limit this to variables from [Sys_poll] *)
+         field_o "enabled_if" (Syntax.since Stanza.syntax (3, 21) >>> enabled_if)
        and+ info = Package_info.decode ~since:(2, 0) ()
        and+ tags = field "tags" (enter (repeat string)) ~default:[]
        and+ exclusive_dir =
@@ -180,6 +192,7 @@ let decode =
        ; opam_file
        ; original_opam_file = None
        ; exclusive_dir
+       ; enabled_if
        }
 ;;
 
@@ -208,6 +221,7 @@ let to_dyn
       ; opam_file = _
       ; original_opam_file = _
       ; exclusive_dir = _
+      ; enabled_if
       }
   =
   let open Dyn in
@@ -225,6 +239,7 @@ let to_dyn
     ; "deprecated_package_names", Name.Map.to_dyn Loc.to_dyn_hum deprecated_package_names
     ; "sites", Site.Map.to_dyn Section.to_dyn sites
     ; "allow_empty", Bool allow_empty
+    ; "enabled_if", (option Blang.to_dyn) enabled_if
     ]
 ;;
 
@@ -241,6 +256,7 @@ let create
       ~conflicts
       ~depends
       ~depopts
+      ~enabled_if
       ~info
       ~has_opam_file
       ~dir
@@ -272,5 +288,6 @@ let create
   ; original_opam_file
   ; exclusive_dir =
       Option.map contents_basename ~f:(fun (loc, s) -> loc, Path.Source.relative dir s)
+  ; enabled_if
   }
 ;;

src/dune_lang/package.mli

@@ -36,6 +36,7 @@ val tags : t -> string list
 val synopsis : t -> string option
 val info : t -> Package_info.t
 val description : t -> string option
+val enabled_if : t -> Blang.t option
 val id : t -> Id.t
 
 val set_version_and_info
@@ -60,6 +61,7 @@ val create
   -> conflicts:Package_dependency.t list
   -> depends:Package_dependency.t list
   -> depopts:Package_dependency.t list
+  -> enabled_if:Blang.t option
   -> info:Package_info.t
   -> has_opam_file:opam_file
   -> dir:Path.Source.t

src/dune_lang/package_constraint.ml

@@ -34,7 +34,7 @@ end
 
 module T = struct
   type t =
-    | Bvar of Package_variable_name.t
+    | Bvar of Value.t
     | Uop of Relop.t * Value.t
     | Bop of Relop.t * Value.t * Value.t
     | And of t list
@@ -44,7 +44,7 @@ module T = struct
   let rec to_dyn =
     let open Dyn in
     function
-    | Bvar v -> variant "Bvar" [ Package_variable_name.to_dyn v ]
+    | Bvar v -> variant "Bvar" [ Value.to_dyn v ]
     | Uop (b, x) -> variant "Uop" [ Relop.to_dyn b; Value.to_dyn x ]
     | Bop (b, x, y) -> variant "Bop" [ Relop.to_dyn b; Value.to_dyn x; Value.to_dyn y ]
     | And t -> variant "And" (List.map ~f:to_dyn t)
@@ -55,7 +55,7 @@ module T = struct
   let rec compare a b =
     let open Ordering.O in
     match a, b with
-    | Bvar a, Bvar b -> Package_variable_name.compare a b
+    | Bvar a, Bvar b -> Value.compare a b
     | Bvar _, _ -> Lt
     | _, Bvar _ -> Gt
     | Uop (a_op, a_value), Uop (b_op, b_value) ->
@@ -85,7 +85,10 @@ include Comparable.Make (T)
 let rec encode c =
   let open Encoder in
   match c with
-  | Bvar x -> Package_variable_name.Project.encode x
+  | Bvar (String_literal _) ->
+    (* We aren't ever able to decode these *)
+    assert false
+  | Bvar (Variable x) -> Package_variable_name.Project.encode x
   | Uop (op, x) -> pair Relop.encode Value.encode (op, x)
   | Bop (op, x, y) -> triple Relop.encode Value.encode Value.encode (op, x, y)
   | And conjuncts -> list sexp (string "and" :: List.map ~f:encode conjuncts)
@@ -154,7 +157,7 @@ let decode =
     >>= function
     | Atom (_loc, A s) when String.is_prefix s ~prefix:":" ->
       let+ () = junk in
-      Bvar (Package_variable_name.of_string (String.drop s 1))
+      Bvar (Variable (Package_variable_name.of_string (String.drop s 1)))
     | _ -> sum (ops @ logops))
 ;;
 

src/dune_lang/package_constraint.mli

@@ -13,7 +13,7 @@ end
     represent strings and booleans. If a variable appears in a position where a
     boolean is expected it will be assumed to represent a boolean. *)
 type t =
-  | Bvar of Package_variable_name.t (** A boolean variable *)
+  | Bvar of Value.t
   | Uop of Relop.t * Value.t
   (** A unary operator applied to a value. Unary operators are operators
       whose LHS is implied by context. E.g. when placing version constraints

src/dune_lang/package_dependency.ml

@@ -61,7 +61,8 @@ let check_for_typo ~loc { name; constraint_ } =
           ]
     in
     Some message
-  | Some (Bvar var) when String.equal (Package_variable_name.to_string var) "with_test" ->
+  | Some (Bvar (Variable var))
+    when String.equal (Package_variable_name.to_string var) "with_test" ->
     let message =
       User_message.make
         ~loc

src/dune_lang/pform.ml

@@ -649,6 +649,10 @@ module Env = struct
       }
   ;;
 
+  let os ~version =
+    List.map Var.Os.all ~f:(fun v -> Var.Os.to_string v, since ~version (Var.Os v))
+  ;;
+
   let initial =
     let macros =
       let macro (x : Macro.t) = No_info x in
@@ -766,11 +770,8 @@ module Env = struct
         ; "dune-warnings", since ~version:(3, 21) Var.Dune_warnings
         ]
       in
-      let os =
-        List.map Var.Os.all ~f:(fun v ->
-          Var.Os.to_string v, since ~version:(3, 20) (Var.Os v))
-      in
-      String.Map.of_list_exn (List.concat [ lowercased; uppercased; other; os ])
+      String.Map.of_list_exn
+        (List.concat [ lowercased; uppercased; other; os ~version:(3, 20) ])
     in
     fun ~stanza:syntax_version ~extensions ->
       let extensions =
@@ -779,6 +780,21 @@ module Env = struct
       { syntax_version; syntax_lang = Stanza.syntax; vars; macros; extensions }
   ;;
 
+  let package_enabled_if =
+    let syntax_version = 3, 21 in
+    let vars =
+      let os = os ~version:syntax_version in
+      (* CR rgrinberg: This has to be disabled for multi context builds *)
+      ("architecture", No_info Var.Architecture) :: os
+    in
+    { syntax_version = 3, 21
+    ; syntax_lang = Stanza.syntax
+    ; vars = String.Map.of_list_exn vars
+    ; macros = String.Map.empty
+    ; extensions = Syntax.Map.singleton Stanza.syntax syntax_version
+    }
+  ;;
+
   let lt_renamed_input_file t =
     { t with
       vars =

src/dune_lang/pform.mli

@@ -204,6 +204,7 @@ module Env : sig
     -> extensions:(Syntax.t * Syntax.Version.t) list
     -> t
 
+  val package_enabled_if : t
   val add_user_vars : t -> string list -> t
   val parse : t -> Template.Pform.t -> pform
 

src/dune_pkg/opam_file.ml

@@ -282,6 +282,7 @@ let load_opam_file_with_contents ~contents:opam_file_string file name =
     ~conflicts:[]
     ~depends:[]
     ~depopts:[]
+    ~enabled_if:None (* CR-someday rgrinberg: would be nice to interpret this *)
     ~info
     ~synopsis:(get_one "synopsis")
     ~description:(get_one "description")