describe: move dummy --lang argument into own module

Signed-off-by: Ali Caglayan <[email protected]>

Author: Alizter

bin/describe/describe_external_lib_deps.ml

@@ -160,14 +160,7 @@ let to_dyn context_name external_resolved_libs =
 let term =
   let+ common = Common.term
   and+ context_name = Common.context_arg ~doc:"Build context to use."
-  and+ _ =
-    Arg.(
-      value
-      & opt (some string) None
-      & info [ "lang" ] ~docv:"VERSION"
-          ~doc:
-            "This argument has no effect and is deprecated. It exists solely \
-             for backwards compatibility.")
+  and+ _ = Describe_lang_compat.arg
   and+ format = Describe_format.arg in
   let config = Common.init common in
   Scheduler.go ~common ~config @@ fun () ->

bin/describe/describe_lang_compat.ml

@@ -0,0 +1,8 @@
+let arg =
+  Arg.(
+    value
+    & opt (some string) None
+    & info [ "lang" ] ~docv:"VERSION"
+        ~doc:
+          "This argument has no effect and is deprecated. It exists solely for \
+           backwards compatibility.")

bin/describe/describe_lang_compat.mli

@@ -0,0 +1,5 @@
+(** Dune describe commands used to take a --lang arugment that did nothing
+    expect for dune describe workspace. To keep compatilbility with accepting
+    such an argument we provide a dummy argument here that can be used. It's
+    value will typically be ignored. *)
+val arg : string option Cmdliner.Term.t

bin/describe/describe_opam_files.ml

@@ -4,15 +4,7 @@ open Stdune
 let term =
   let+ common = Common.term
   and+ format = Describe_format.arg
-  and+ _ =
-    Arg.(
-      value
-      & opt (some string) None
-      & info [ "lang" ] ~docv:"VERSION"
-          ~doc:
-            "This argument has no effect and is deprecated. It exists solely \
-             for backwards compatibility.")
-  in
+  and+ _ = Describe_lang_compat.arg in
   let config = Common.init common in
   Scheduler.go ~common ~config @@ fun () ->
   Build_system.run_exn @@ fun () ->

bin/describe/describe_pp.ml

@@ -95,14 +95,7 @@ let get_pped_file super_context file =
 let term =
   let+ common = Common.term
   and+ context_name = Common.context_arg ~doc:"Build context to use."
-  and+ _ =
-    Arg.(
-      value
-      & opt (some string) None
-      & info [ "lang" ] ~docv:"VERSION"
-          ~doc:
-            "This argument has no effect and is deprecated. It exists solely \
-             for backwards compatibility.")
+  and+ _ = Describe_lang_compat.arg
   and+ file =
     Arg.(required & pos 0 (some string) None (Arg.info [] ~docv:"FILE"))
   in