refactor(cache): use cmdliner groups in dune cache commands

We also do some cleanup of the documentation. This will make adding
more subcommands easier in the future.

closes #4471

<!-- ps-id: 60b331a0-d183-498b-9bba-5ea3d4538fb2 -->

Signed-off-by: Ali Caglayan <alizter@gmail.com>

bin/cache.ml

@@ -1,85 +1,28 @@
 open Stdune
 open Import
 
-let name = "cache"
-
 (* CR-someday amokhov: Implement other commands supported by Jenga. *)
 
-let man =
-  [ `S "DESCRIPTION"
-  ; `P
-      {|Dune can share build artifacts between workspaces. Currently, the only
-        action supported by this command is `trim`, but we plan to provide more
-        functionality soon. |}
-  ; `S "ACTIONS"
-  ; `P {|$(b,trim) trim the shared cache to free space.|}
-  ; `S "EXAMPLES"
-  ; `Pre
-      {|Trimming the Dune cache to 1 GB.
-
-        \$ dune cache trim --trimmed-size=1GB |}
-  ; `Pre
-      {|Trimming 500 MB from the Dune cache.
-
-        \$ dune cache trim --size=500MB |}
-  ; `Blocks Common.help_secs
-  ]
-
-let doc = "Manage the shared cache of build artifacts"
+let trim =
+  let info =
+    let doc = "Trim the Dune cache" in
+    let man =
+      [ `P "Trim the Dune cache to a specified size or by a specified amount."
+      ; `S "EXAMPLES"
+      ; `Pre
+          {|Trimming the Dune cache to 1 GB.
 
-let info = Cmd.info name ~doc ~man
+           \$ dune cache trim --trimmed-size=1GB |}
+      ; `Pre
+          {|Trimming 500 MB from the Dune cache.
 
-let trim ~trimmed_size ~size =
-  Log.init_disabled ();
-  let open Result.O in
-  match
-    let+ goal =
-      match (trimmed_size, size) with
-      | Some trimmed_size, None -> Result.Ok trimmed_size
-      | None, Some size ->
-        Result.Ok (Int64.sub (Dune_cache.Trimmer.overhead_size ()) size)
-      | _ -> Result.Error "specify either --size or --trimmed-size"
+           \$ dune cache trim --size=500MB |}
+      ]
     in
-    Dune_cache.Trimmer.trim ~goal
-  with
-  | Error s -> User_error.raise [ Pp.text s ]
-  | Ok { trimmed_bytes } ->
-    User_message.print
-      (User_message.make [ Pp.textf "Freed %s" (Bytes_unit.pp trimmed_bytes) ])
-
-type mode =
-  | Trim
-  | Start_deprecated
-  | Stop_deprecated
-
-let modes =
-  [ ("start", Start_deprecated); ("stop", Stop_deprecated); ("trim", Trim) ]
-
-(* CR-someday amokhov: See https://github.com/ocaml/dune/issues/4471. *)
-
-(* We don't want to list deprecated subcommands in help. *)
-let non_deprecated_modes = [ ("trim", Trim) ]
-
-(* We do want to print a nice error message if a deprecated subcommand is
-   run. *)
-let deprecated_error () =
-  User_error.raise
-    [ Pp.text
-        "Dune no longer uses the cache daemon, and so the `start` and `stop` \
-         subcommands of `dune cache` were removed."
-    ]
-
-let term =
-  Term.ret
-  @@ let+ mode =
-       Arg.(
-         value
-         & pos 0 (some (enum modes)) None
-         & info [] ~docv:"ACTION"
-             ~doc:
-               (Printf.sprintf "The cache action to perform (%s)"
-                  (Arg.doc_alts_enum non_deprecated_modes)))
-     and+ trimmed_size =
+    Cmd.info "trim" ~doc ~man
+  in
+  Cmd.v info
+  @@ let+ trimmed_size =
        Arg.(
          value
          & opt (some bytes) None
@@ -91,9 +34,35 @@ let term =
          & opt (some bytes) None
          & info ~docv:"BYTES" [ "size" ] ~doc:"Size to trim the cache to.")
      in
-     match mode with
-     | Some Trim -> `Ok (trim ~trimmed_size ~size)
-     | Some Start_deprecated | Some Stop_deprecated -> deprecated_error ()
-     | None -> `Help (`Pager, Some name)
+     Log.init_disabled ();
+     let open Result.O in
+     match
+       let+ goal =
+         match (trimmed_size, size) with
+         | Some trimmed_size, None -> Result.Ok trimmed_size
+         | None, Some size ->
+           Result.Ok (Int64.sub (Dune_cache.Trimmer.overhead_size ()) size)
+         | _ -> Result.Error "please specify either --size or --trimmed-size"
+       in
+       Dune_cache.Trimmer.trim ~goal
+     with
+     | Error s -> User_error.raise [ Pp.text s ]
+     | Ok { trimmed_bytes } ->
+       User_message.print
+         (User_message.make
+            [ Pp.textf "Freed %s" (Bytes_unit.pp trimmed_bytes) ])
 
-let command = Cmd.v info term
+let command =
+  let info =
+    let doc = "Manage the shared cache of build artifacts" in
+    let man =
+      [ `S "DESCRIPTION"
+      ; `P
+          "Dune can share build artifacts between workspaces. Currently, the \
+           only action supported by this command is `trim`, but we plan to \
+           provide more functionality soon."
+      ]
+    in
+    Cmd.info "cache" ~doc ~man
+  in
+  Cmd.group info [ trim ]