Fix META generation for private libs.

CHANGES.md

@@ -1,6 +1,8 @@
 Unreleased
 ----------
 
+- Fixes `opam` META file requires entry for private libs (#4841, fixes #4839, @toots)
+
 - Fixes `dune exec` not adding .exe on Windows (#4371, fixes #3322, @MisterDA)
 
 - Allow multiple cinaps stanzas in the same directory (#4460, @rgrinberg)

src/dune_rules/gen_meta.ml

@@ -89,7 +89,14 @@ let gen_lib pub_name lib ~path ~version =
     | Ppx_deriver _ ->
       [ Pos "ppx_driver" ]
   in
-  let to_names = Lib_name.Set.of_list_map ~f:Lib.name in
+  let name lib =
+    let name = Lib.name lib in
+    match Lib_info.status (Lib.info lib) with
+    | Private (_, Some pkg) ->
+      Lib_name.mangled (Package.name pkg) (Lib_name.to_local_exn name)
+    | _ -> name
+  in
+  let to_names = Lib_name.Set.of_list_map ~f:name in
   let* lib_deps = Resolve.read_memo_build (Lib.requires lib) >>| to_names in
   let* ppx_rt_deps =
     Resolve.read_memo_build (Lib.ppx_runtime_deps lib) >>| to_names

test/blackbox-tests/test-cases/private-package-lib.t/run.t

@@ -62,7 +62,7 @@ Note the name mangling convention in the META file:
   package "bar" (
     directory = "bar"
     description = ""
-    requires = "secret"
+    requires = "foo.__private__.secret"
     archive(byte) = "foo.cma"
     archive(native) = "foo.cmxa"
     plugin(byte) = "foo.cma"