Remove support for old style subsystems

CHANGES.md

@@ -62,6 +62,9 @@
   The global configuration merely specifies the default. 
   (#2213, @aalekseyev, @jdimino)
 
+- Remove support for old style subsystems. Dune will now emit a warning to
+  reinstall the library with the old style subsystem. (#2480, @rgrinberg)
+
 1.11.0 (23/07/2019)
 -------------------
 

src/findlib.ml

@@ -212,11 +212,17 @@ module Package = struct
   let to_dune t =
     let loc = loc t in
     let add_loc x = (loc, x) in
-    let sub_systems =
-      match dune_file t with
-      | None -> Sub_system_name.Map.empty
-      | Some p -> Installed_dune_file.load p
+    let () =
+      dune_file t
+      |> Option.iter ~f:(fun p ->
+        User_warning.emit ~loc:(Loc.in_file p)
+          [ Pp.text
+              ".dune files are ignored since 2.0. Reinstall the library with \
+               dune >= 2.0 to get rid of this warning and enable support for \
+               the subsystem this library provides."
+          ])
     in
+    let sub_systems = Sub_system_name.Map.empty in
     let archives = archives t in
     let obj_dir = Obj_dir.make_external_no_private ~dir:t.dir in
     let modes : Mode.Dict.Set.t =

test/blackbox-tests/test-cases/old-dune-subsystem/run.t

@@ -5,3 +5,12 @@ we understand the old files.
 
   $ env OCAMLPATH=install/lib dune runtest --root example
   Entering directory 'example'
+  File "$TESTCASE_ROOT/install/lib/dune_inline_tests/dune_inline_tests.dune", line 1, characters 0-0:
+  Warning: .dune files are ignored since 2.0. Reinstall the library with dune
+  >= 2.0 to get rid of this warning and enable support for the subsystem this
+  library provides.
+  File "src/dune", line 3, characters 25-42:
+  3 |   (inline_tests (backend dune_inline_tests)))
+                               ^^^^^^^^^^^^^^^^^
+  Error: dune_inline_tests is not an inline tests backend
+  [1]