Ignore <package>.opam when <package> is empty

bin/main.ml

@@ -70,7 +70,7 @@ let find_root () =
     if String_set.mem "jbuild-workspace" files then
       cont counter ~candidates:((0, dir, to_cwd) :: candidates) dir ~to_cwd
     else if String_set.exists files ~f:(fun fn ->
-        String.is_suffix fn ~suffix:".opam") then
+        String.is_suffix fn ~suffix:".opam" && fn <> ".opam") then
       cont counter ~candidates:((1, dir, to_cwd) :: candidates) dir ~to_cwd
     else if String_set.mem ".git" files || String_set.mem ".hg" files then
       cont counter ~candidates:((2, dir, to_cwd) :: candidates) dir ~to_cwd

doc/manual.org

@@ -152,6 +152,9 @@ only declare parts of the packages in this subtree. Typically your
 =<package>.opam= files should be at the root of your project, since
 this is where =opam pin ...= will look for them.
 
+Note that =<package>= must be non empty, so in particular =.opam=
+files are ignored.
+
 *** Package version
 
 Note that Jbuilder will try to determine the version number of
@@ -985,7 +988,7 @@ Jbuilder looks for the following entries in all these directories, in
 order of precedences:
 
 1. =jbuild-workspace=
-2. any file ending with =.opam=
+2. any file ending with =.opam=, except =.opam= itself
 3. =.git= or =.hg=
 
 The first entry to match in this list will determine the root. If this

src/jbuild_load.ml

@@ -148,7 +148,7 @@ let load () =
       let path = File_tree.Dir.path dir in
       String_set.fold (File_tree.Dir.files dir) ~init:acc ~f:(fun fn acc ->
         match Filename.split_ext fn with
-        | Some (pkg, ".opam") ->
+        | Some (pkg, ".opam") when pkg <> "" ->
           let version_from_opam_file =
             let lines = lines_of_file (Path.relative path fn |> Path.to_string) in
             List.find_map lines ~f:(fun s ->