Support (package) in (mdx)

This adds a (package) field to (mdx) with the usual semantics.

The syntax is not ideal since (packages) is already supported as sugar
to specify dependencies.

Closes ocaml#3756

Signed-off-by: Etienne Millon <me@emillon.org>

src/dune_rules/dune_file.ml

@@ -2074,6 +2074,14 @@ module Generate_sites_module = struct
        { loc; module_; sourceroot; relocatable; sites; plugins })
 end
 
+module Package_proxy = struct
+  type Stanza.t +=
+    | T of
+        { package : Package.t option
+        ; stanza : Stanza.t
+        }
+end
+
 type Stanza.t +=
   | Library of Library.t
   | Foreign_library of Foreign.Library.t
@@ -2264,6 +2272,7 @@ let stanza_package = function
   | Tests { package = Some package; _ } ->
     Some package
   | Coq_stanza.Theory.T { package = Some package; _ } -> Some package
+  | Package_proxy.T { package; _ } -> package
   | _ -> None
 
 type t =

src/dune_rules/dune_file.mli

@@ -405,6 +405,19 @@ module Generate_sites_module : sig
     }
 end
 
+module Package_proxy : sig
+  (** A wrapper to implement the (package) field on a stanza that does not
+      support it. This also helps with dependency cycles since [stanza_package]
+      (used to filter irrelevant stanzas) is part of [Dune_file] and can not
+      depend on all stanzas. *)
+
+  type Stanza.t +=
+    | T of
+        { package : Package.t option
+        ; stanza : Stanza.t
+        }
+end
+
 type Stanza.t +=
   | Library of Library.t
   | Foreign_library of Foreign.Library.t

src/dune_rules/gen_rules.ml

@@ -68,86 +68,90 @@ end = struct
   let of_stanza stanza ~sctx ~src_dir ~ctx_dir ~scope ~dir_contents ~expander
       ~files_to_install =
     let dir = ctx_dir in
-    match stanza with
-    | Toplevel toplevel ->
-      let+ () = Toplevel_rules.setup ~sctx ~dir ~toplevel in
-      empty_none
-    | Library lib
-      when Lib.DB.available (Scope.libs scope) (Dune_file.Library.best_name lib)
-      ->
-      let+ cctx, merlin =
-        Lib_rules.rules lib ~sctx ~dir ~scope ~dir_contents ~expander
-      in
-      { merlin = Some merlin
-      ; cctx = Some (lib.buildable.loc, cctx)
-      ; js = None
-      ; source_dirs = None
-      }
-    | Foreign_library lib ->
-      let+ () =
-        Lib_rules.foreign_rules lib ~sctx ~dir ~dir_contents ~expander
-      in
-      empty_none
-    | Executables exes -> (
-      Expander.eval_blang expander exes.enabled_if >>= function
-      | false -> Memo.Build.return empty_none
-      | true ->
-        let* () =
-          Memo.Build.Option.iter exes.install_conf ~f:files_to_install
+    let rec go stanza =
+      match stanza with
+      | Toplevel toplevel ->
+        let+ () = Toplevel_rules.setup ~sctx ~dir ~toplevel in
+        empty_none
+      | Library lib
+        when Lib.DB.available (Scope.libs scope)
+               (Dune_file.Library.best_name lib) ->
+        let+ cctx, merlin =
+          Lib_rules.rules lib ~sctx ~dir ~scope ~dir_contents ~expander
         in
+        { merlin = Some merlin
+        ; cctx = Some (lib.buildable.loc, cctx)
+        ; js = None
+        ; source_dirs = None
+        }
+      | Foreign_library lib ->
+        let+ () =
+          Lib_rules.foreign_rules lib ~sctx ~dir ~dir_contents ~expander
+        in
+        empty_none
+      | Executables exes -> (
+        Expander.eval_blang expander exes.enabled_if >>= function
+        | false -> Memo.Build.return empty_none
+        | true ->
+          let* () =
+            Memo.Build.Option.iter exes.install_conf ~f:files_to_install
+          in
+          let+ cctx, merlin =
+            Exe_rules.rules exes ~sctx ~dir ~scope ~expander ~dir_contents
+          in
+          { merlin = Some merlin
+          ; cctx = Some (exes.buildable.loc, cctx)
+          ; js =
+              Some
+                (List.concat_map exes.names ~f:(fun (_, exe) ->
+                     List.map
+                       [ exe ^ ".bc.js"; exe ^ ".bc.runtime.js" ]
+                       ~f:(Path.Build.relative dir)))
+          ; source_dirs = None
+          })
+      | Alias alias ->
+        let+ () = Simple_rules.alias sctx alias ~dir ~expander in
+        empty_none
+      | Tests tests ->
         let+ cctx, merlin =
-          Exe_rules.rules exes ~sctx ~dir ~scope ~expander ~dir_contents
+          Test_rules.rules tests ~sctx ~dir ~scope ~expander ~dir_contents
         in
         { merlin = Some merlin
-        ; cctx = Some (exes.buildable.loc, cctx)
-        ; js =
-            Some
-              (List.concat_map exes.names ~f:(fun (_, exe) ->
-                   List.map
-                     [ exe ^ ".bc.js"; exe ^ ".bc.runtime.js" ]
-                     ~f:(Path.Build.relative dir)))
+        ; cctx = Some (tests.exes.buildable.loc, cctx)
+        ; js = None
         ; source_dirs = None
-        })
-    | Alias alias ->
-      let+ () = Simple_rules.alias sctx alias ~dir ~expander in
-      empty_none
-    | Tests tests ->
-      let+ cctx, merlin =
-        Test_rules.rules tests ~sctx ~dir ~scope ~expander ~dir_contents
-      in
-      { merlin = Some merlin
-      ; cctx = Some (tests.exes.buildable.loc, cctx)
-      ; js = None
-      ; source_dirs = None
-      }
-    | Copy_files { files = glob; _ } ->
-      let* source_dirs =
-        let loc = String_with_vars.loc glob in
-        let+ src_glob = Expander.No_deps.expand_str expander glob in
-        if Filename.is_relative src_glob then
-          Some
-            (Path.Source.relative src_dir src_glob ~error_loc:loc
-            |> Path.Source.parent_exn)
-        else
-          None
-      in
-      Memo.Build.return { merlin = None; cctx = None; js = None; source_dirs }
-    | Install i ->
-      let+ () = files_to_install i in
-      empty_none
-    | Plugin p ->
-      let+ () = Plugin_rules.setup_rules ~sctx ~dir p in
-      empty_none
-    | Cinaps.T cinaps ->
-      let+ () = Cinaps.gen_rules sctx cinaps ~dir ~scope in
-      empty_none
-    | Mdx.T mdx -> (
-      Expander.eval_blang expander (Mdx.enabled_if mdx) >>= function
-      | false -> Memo.Build.return empty_none
-      | true ->
-        let+ () = Mdx.gen_rules ~sctx ~dir ~expander mdx in
-        empty_none)
-    | _ -> Memo.Build.return empty_none
+        }
+      | Copy_files { files = glob; _ } ->
+        let* source_dirs =
+          let loc = String_with_vars.loc glob in
+          let+ src_glob = Expander.No_deps.expand_str expander glob in
+          if Filename.is_relative src_glob then
+            Some
+              (Path.Source.relative src_dir src_glob ~error_loc:loc
+              |> Path.Source.parent_exn)
+          else
+            None
+        in
+        Memo.Build.return { merlin = None; cctx = None; js = None; source_dirs }
+      | Install i ->
+        let+ () = files_to_install i in
+        empty_none
+      | Plugin p ->
+        let+ () = Plugin_rules.setup_rules ~sctx ~dir p in
+        empty_none
+      | Cinaps.T cinaps ->
+        let+ () = Cinaps.gen_rules sctx cinaps ~dir ~scope in
+        empty_none
+      | Mdx.T mdx -> (
+        Expander.eval_blang expander (Mdx.enabled_if mdx) >>= function
+        | false -> Memo.Build.return empty_none
+        | true ->
+          let+ () = Mdx.gen_rules ~sctx ~dir ~expander mdx in
+          empty_none)
+      | Package_proxy.T { stanza; _ } -> go stanza
+      | _ -> Memo.Build.return empty_none
+    in
+    go stanza
 
   let of_stanzas stanzas ~cctxs ~sctx ~src_dir ~ctx_dir ~scope ~dir_contents
       ~expander ~files_to_install =

src/dune_rules/mdx.ml

@@ -153,14 +153,21 @@ let decode =
      and+ preludes = field ~default:[] "preludes" (repeat Prelude.decode)
      and+ enabled_if =
        Enabled_if.decode ~allowed_vars:Any ~since:(Some (2, 9)) ()
+     and+ package =
+       Stanza_common.Pkg.field_opt ()
+         ~check:(Dune_lang.Syntax.since Stanza.syntax (2, 9))
      in
-     { loc; files; packages; preludes; enabled_if })
+     (package, { loc; files; packages; preludes; enabled_if }))
 
 let () =
   let open Dune_lang.Decoder in
   let decode = Dune_lang.Syntax.since Stanza.syntax (2, 4) >>> decode in
   Dune_project.Extension.register_simple syntax
-    (return [ ("mdx", decode >>| fun x -> [ T x ]) ])
+    (return
+       [ ( "mdx"
+         , decode >>| fun (package, x) ->
+           [ Dune_file.Package_proxy.T { package; stanza = T x } ] )
+       ])
 
 (** Returns the list of files (in _build) to be passed to mdx for the given
     stanza and context *)

test/blackbox-tests/test-cases/mdx-stanza.t/package-old-lang-dune/doc-a.md

@@ -0,0 +1,3 @@
+```ocaml
+# let x = 1;;
+```

test/blackbox-tests/test-cases/mdx-stanza.t/package-old-lang-dune/doc-b.md

@@ -0,0 +1,3 @@
+```ocaml
+# let x = 1;;
+```

test/blackbox-tests/test-cases/mdx-stanza.t/package-old-lang-dune/dune

@@ -0,0 +1,7 @@
+(mdx
+ (files doc-a.md)
+ (package a))
+
+(mdx
+ (files doc-b.md)
+ (package b))

test/blackbox-tests/test-cases/mdx-stanza.t/package-old-lang-dune/dune-project

@@ -0,0 +1,2 @@
+(lang dune 2.8)
+(using mdx 0.1)

test/blackbox-tests/test-cases/mdx-stanza.t/package/doc-a.md

@@ -0,0 +1,3 @@
+```ocaml
+# let x = 1;;
+```

test/blackbox-tests/test-cases/mdx-stanza.t/package/doc-b.md

@@ -0,0 +1,3 @@
+```ocaml
+# let x = 1;;
+```

test/blackbox-tests/test-cases/mdx-stanza.t/package/dune

@@ -0,0 +1,7 @@
+(mdx
+ (files doc-a.md)
+ (package a))
+
+(mdx
+ (files doc-b.md)
+ (package b))

test/blackbox-tests/test-cases/mdx-stanza.t/package/dune-project

@@ -0,0 +1,2 @@
+(lang dune 2.9)
+(using mdx 0.1)

test/blackbox-tests/test-cases/mdx-stanza.t/run.t

@@ -91,3 +91,23 @@ The mdx stanza supports (enabled_if):
   Error: 'enabled_if' is only available since version 2.9 of the dune language.
   Please update your dune-project file to have (lang dune 2.9).
   [1]
+
+The mdx stanza supports (package):
+
+  $ dune runtest --root package --only-packages b
+  Entering directory 'package'
+  File "doc-b.md", line 1, characters 0-0:
+  Error: Files _build/default/doc-b.md and
+  _build/default/.mdx/doc-b.md.corrected differ.
+  [1]
+
+(package) needs a recent (lang dune):
+
+  $ dune runtest --root package-old-lang-dune --only-packages b
+  Entering directory 'package-old-lang-dune'
+  File "dune", line 3, characters 1-12:
+  3 |  (package a))
+       ^^^^^^^^^^^
+  Error: 'package' is only available since version 2.9 of the dune language.
+  Please update your dune-project file to have (lang dune 2.9).
+  [1]