fix: do not re-run jbuild syntax dune files on every run

While this is more correct, it ends up being too slow in practice
especially since we don't have cut-off on the results

Signed-off-by: Rudi Grinberg <me@rgrinberg.com>

<!-- ps-id: 9d1157e2-de9a-4b99-9bd5-3a76490d42d7 -->

CHANGES.md

@@ -1,6 +1,9 @@
 Unreleased
 ----------
 
+- Do not re-run jbuild syntax files on every iteration of the watch mode. This
+  is too memory consuming. (#.., fix #6900, @rgrinberg)
+
 - Fix a crash when using a version of Coq < 8.13 due to the native compiler
   config variable being missing. We now explicitly default to `(mode vo)` for
   these older versions of Coq. (#7847, fixes #7846, @Alizter)

src/dune_rules/dune_load.ml

@@ -153,7 +153,6 @@ module Script = struct
     in
     let ocaml = Action.Prog.ok_exn context.ocaml.ocaml in
     let* () =
-      let* (_ : Memo.Run.t) = Memo.current_run () in
       Memo.of_reproducible_fiber
         (Process.run Strict ~display:Quiet ~dir:(Path.source dir)
            ~env:context.env ocaml args)