refactor(dune_lang): misc refactoring for consistency (#7934)

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

src/dune_rules/dune_file.ml

@@ -625,7 +625,9 @@ module Library = struct
          let+ _ = field_b "no_keep_locs" ~check in
          ()
        and+ sub_systems =
-         let* () = return () in
+         return ()
+         >>> (* CR rgrinberg: weird that we have to remember to delay this. Can't
+                this be pushed down to the [record_parser] itself *)
          Sub_system_info.record_parser ()
        and+ virtual_modules =
          field_o "virtual_modules"
@@ -641,8 +643,8 @@ module Library = struct
            >>> located Lib_name.decode)
        and+ private_modules =
          field_o "private_modules"
-           (let* () = Dune_lang.Syntax.since Stanza.syntax (1, 2) in
-            Ordered_set_lang.decode)
+           (Dune_lang.Syntax.since Stanza.syntax (1, 2)
+           >>> Ordered_set_lang.decode)
        and+ stdlib =
          field_o "stdlib"
            (Dune_lang.Syntax.since Ocaml_stdlib.syntax (0, 1)
@@ -1750,8 +1752,8 @@ module Rule = struct
       | Action -> short_form
       | Since (version, inner) ->
         let what = Printf.sprintf "'%s' in short-form 'rule'" atom in
-        let* () = Dune_lang.Syntax.since ~what Stanza.syntax version in
-        interpret atom inner
+        Dune_lang.Syntax.since ~what Stanza.syntax version
+        >>> interpret atom inner
     in
     peek_exn >>= function
     | List (_, Atom (loc, A s) :: _) -> (
@@ -1872,13 +1874,9 @@ module Alias_conf = struct
           and+ package = field_o "package" Stanza_common.Pkg.decode
           and+ action =
             field_o "action"
-              (let extra_info =
-                 "Use a rule stanza with the alias field instead"
-               in
-               let* () =
-                 Dune_lang.Syntax.deleted_in ~extra_info Stanza.syntax (2, 0)
-               in
-               located Dune_lang.Action.decode_dune_file)
+              (Dune_lang.Syntax.deleted_in Stanza.syntax (2, 0)
+                 ~extra_info:"Use a rule stanza with the alias field instead"
+              >>> located Dune_lang.Action.decode_dune_file)
           and+ loc = loc
           and+ locks = Locks.field ()
           and+ enabled_if =