Support (package) in (mdx) (#4691)

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 #3756

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

CHANGES.md

@@ -159,6 +159,8 @@ Unreleased
 
 - Add `(enabled_if ...)` to `(mdx ...)` (#4434, @emillon)
 
+- Add `(package ...)` to `(mdx ...)` (#4691, fixes #3756, @emillon)
+
 2.8.5 (28/03/2021)
 ------------------
 

doc/dune-files.rst

@@ -1881,6 +1881,15 @@ Where ``<optional-fields>`` are:
   See `MDX's documentation <https://github.com/realworldocaml/mdx>`__ for more
   details on preludes.
 
+- ``(enabled_if <blang expression>)`` is the same as the corresponding field of
+  `library`_.
+
+- ``(package <package>)`` specifies which package to attach this stanza to
+  (similarly to when ``(package)`` is attached to a ``(rule)`` stanza. When
+  ``-p`` is passed, ``(mdx)`` stanzas with an other package will be ignored.
+  Note that this is feature is completely separate from ``(packages)``, which
+  specifies some dependencies.
+
 .. _plugin:
 
 plugin (since 2.8)

src/dune_rules/mdx.ml

@@ -127,6 +127,7 @@ type t =
   ; packages : (Loc.t * Package.Name.t) list
   ; preludes : Prelude.t list
   ; enabled_if : Blang.t
+  ; package : Package.t option
   }
 
 let enabled_if t = t.enabled_if
@@ -153,8 +154,11 @@ 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 })
+     { loc; files; packages; preludes; enabled_if; package })
 
 let () =
   let open Dune_lang.Decoder in
@@ -228,10 +232,22 @@ let gen_rules_for_single_file stanza ~sctx ~dir ~expander ~mdx_prog src =
 (** Generates the rules for a given mdx stanza *)
 let gen_rules t ~sctx ~dir ~expander =
   let open Memo.Build.O in
-  let* files_to_mdx = files_to_mdx t ~sctx ~dir
-  and* mdx_prog =
-    Super_context.resolve_program sctx ~dir ~loc:(Some t.loc)
-      ~hint:"opam install mdx" "ocaml-mdx"
+  let register_rules () =
+    let* files_to_mdx = files_to_mdx t ~sctx ~dir
+    and* mdx_prog =
+      Super_context.resolve_program sctx ~dir ~loc:(Some t.loc)
+        ~hint:"opam install mdx" "ocaml-mdx"
+    in
+    Memo.Build.parallel_iter files_to_mdx
+      ~f:(gen_rules_for_single_file t ~sctx ~dir ~expander ~mdx_prog)
+  in
+  let* only_packages = Only_packages.get () in
+  let do_it =
+    match (only_packages, t.package) with
+    | None, _
+    | Some _, None ->
+      true
+    | Some only, Some stanza_package ->
+      Package.Name.Map.mem only (Package.name stanza_package)
   in
-  Memo.Build.parallel_iter files_to_mdx
-    ~f:(gen_rules_for_single_file t ~sctx ~dir ~expander ~mdx_prog)
+  Memo.Build.if_ do_it register_rules

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/doc-nopkg.md

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

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

@@ -0,0 +1,10 @@
+(mdx
+ (files doc-a.md)
+ (package a))
+
+(mdx
+ (files doc-b.md)
+ (package b))
+
+(mdx
+ (files doc-nopkg.md))

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/doc-nopkg.md

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

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

@@ -0,0 +1,10 @@
+(mdx
+ (files doc-a.md)
+ (package a))
+
+(mdx
+ (files doc-b.md)
+ (package b))
+
+(mdx
+ (files doc-nopkg.md))

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 +91,39 @@ 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
+  Entering directory 'package'
+  File "doc-a.md", line 1, characters 0-0:
+  Error: Files _build/default/doc-a.md and
+  _build/default/.mdx/doc-a.md.corrected differ.
+  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.
+  File "doc-nopkg.md", line 1, characters 0-0:
+  Error: Files _build/default/doc-nopkg.md and
+  _build/default/.mdx/doc-nopkg.md.corrected differ.
+  [1]
+
+  $ 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.
+  File "doc-nopkg.md", line 1, characters 0-0:
+  Error: Files _build/default/doc-nopkg.md and
+  _build/default/.mdx/doc-nopkg.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]