[install_rules] Allow for stanzas to install files in different packa…

…ges.

In some cases, it is convenient for stanzas to produce objects that
will be installed under different packages.

For example, in Coq we may want to install the costly native files in
a `foo-native` package, or distributions such as Debian like to split
packages in `-doc`, `-dev`, and `-dbg` variants.

This PR modifies the code so this is possible.

This code is cherry-picked from ocaml#4750 (which would be the first user
of the feature), but I am submitting separately as I think the change
deserves more discussion.

For example, this implies that `Dune_file.stanza_package stanza` is not
canonical anymore. Likely, a better modelling would be to introduce
the notion of "sub-package".

The code changes themselves don't make me super-happy, consider them a
draft. If you folks are OK with the idea, I can improve it so the
common case of one stanza installing files only for one package is
better optimized.

Signed-off-by: Emilio Jesus Gallego Arias <[email protected]>

src/dune_rules/install_rules.ml

@@ -255,7 +255,10 @@ end = struct
     List.exists [ "README"; "LICENSE"; "CHANGE"; "HISTORY" ] ~f:(fun prefix ->
         String.is_prefix fn ~prefix)
 
-  let stanza_to_entries ~sctx ~dir ~scope ~expander stanza =
+  (* We allow for an stanza to produce files in different packages *)
+  let stanza_to_entries ~sctx ~dir ~scope ~expander stanza :
+      (Package.Name.t * (Loc.t option * Path.Build.t Install.Entry.t)) list
+      Memo.Build.t =
     let* stanza_and_package =
       let+ stanza = keep_if expander stanza ~scope in
       let open Option.O in
@@ -264,48 +267,49 @@ end = struct
       (stanza, package)
     in
     match stanza_and_package with
-    | None -> Memo.Build.return None
-    | Some (stanza, package) ->
-      let new_entries =
-        match (stanza : Stanza.t) with
-        | Dune_file.Install i
-        | Dune_file.Executables { install_conf = Some i; _ } ->
-          let path_expander =
-            File_binding.Unexpanded.expand ~dir
-              ~f:(Expander.No_deps.expand_str expander)
-          in
-          let section = i.section in
-          Memo.Build.List.map i.files ~f:(fun unexpanded ->
-              let* fb = path_expander unexpanded in
-              let loc = File_binding.Expanded.src_loc fb in
-              let src = File_binding.Expanded.src fb in
-              let dst = File_binding.Expanded.dst fb in
-              let+ entry =
-                Install.Entry.make_with_site section
-                  (Super_context.get_site_of_packages sctx)
-                  src ?dst
-              in
-              (Some loc, entry))
-        | Dune_file.Library lib ->
-          let sub_dir = Dune_file.Library.sub_dir lib in
-          let* dir_contents = Dir_contents.get sctx ~dir in
-          lib_install_files sctx ~scope ~dir ~sub_dir lib ~dir_contents
-        | Coq_stanza.Theory.T coqlib ->
-          Coq_rules.install_rules ~sctx ~dir coqlib
-        | Dune_file.Documentation d ->
-          let* dc = Dir_contents.get sctx ~dir in
-          let+ mlds = Dir_contents.mlds dc d in
-          List.map mlds ~f:(fun mld ->
-              ( None
+    | None -> Memo.Build.return []
+    | Some (stanza, package) -> (
+      let name = Package.name package in
+      match (stanza : Stanza.t) with
+      | Dune_file.Install i
+      | Dune_file.Executables { install_conf = Some i; _ } ->
+        let path_expander =
+          File_binding.Unexpanded.expand ~dir
+            ~f:(Expander.No_deps.expand_str expander)
+        in
+        let section = i.section in
+        Memo.Build.List.map i.files ~f:(fun unexpanded ->
+            let* fb = path_expander unexpanded in
+            let loc = File_binding.Expanded.src_loc fb in
+            let src = File_binding.Expanded.src fb in
+            let dst = File_binding.Expanded.dst fb in
+            let+ entry =
+              Install.Entry.make_with_site section
+                (Super_context.get_site_of_packages sctx)
+                src ?dst
+            in
+            (name, (Some loc, entry)))
+      | Dune_file.Library lib ->
+        let sub_dir = Dune_file.Library.sub_dir lib in
+        let* dir_contents = Dir_contents.get sctx ~dir in
+        lib_install_files sctx ~scope ~dir ~sub_dir lib ~dir_contents
+        >>| List.map ~f:(fun entry -> (name, entry))
+      | Coq_stanza.Theory.T coqlib ->
+        Coq_rules.install_rules ~sctx ~dir coqlib
+        >>| List.map ~f:(fun entry -> (name, entry))
+      | Dune_file.Documentation d ->
+        let* dc = Dir_contents.get sctx ~dir in
+        let+ mlds = Dir_contents.mlds dc d in
+        List.map mlds ~f:(fun mld ->
+            ( name
+            , ( None
               , Install.Entry.make
                   ~dst:(sprintf "odoc-pages/%s" (Path.Build.basename mld))
-                  Section.Doc mld ))
-        | Dune_file.Plugin t -> Plugin_rules.install_rules ~sctx ~dir t
-        | _ -> Memo.Build.return []
-      in
-      let name = Package.name package in
-      let+ entries = new_entries in
-      Some (name, entries)
+                  Section.Doc mld ) ))
+      | Dune_file.Plugin t ->
+        Plugin_rules.install_rules ~sctx ~dir t
+        >>| List.map ~f:(fun entry -> (name, entry))
+      | _ -> Memo.Build.return [])
 
   let stanzas_to_entries sctx =
     let ctx = Super_context.context sctx in
@@ -372,12 +376,10 @@ end = struct
           in
           named_entries :: acc)
       |> Memo.Build.parallel_map ~f:Fun.id
+      |> Memo.Build.map ~f:List.concat
     in
-    List.fold_left l ~init ~f:(fun acc named_entries ->
-        match named_entries with
-        | None -> acc
-        | Some (name, entries) ->
-          Package.Name.Map.Multi.add_all acc name entries)
+    List.fold_left l ~init ~f:(fun acc (name, entry) ->
+        Package.Name.Map.Multi.add_all acc name [ entry ])
     |> Package.Name.Map.map ~f:(fun entries ->
            (* Sort entries so that the ordering in [dune-package] is independent
               of Dune's current implementation. *)