Deprecate let%lwt at the structure item level

ocsigen · Oct 6, 2019 · 403df4a · 403df4a
1 parent 1d44e3b
commit 403df4a
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Showing 3 changed files with 14 additions and 3 deletions.
diff --git a/src/ppx/ppx_lwt.ml b/src/ppx/ppx_lwt.ml
@@ -465,7 +465,15 @@ let mapper =
       default_loc := stri.pstr_loc;
       match stri with
       | [%stri let%lwt [%p? var] = [%e? exp]] ->
-        [%stri let [%p var] = Lwt_main.run [%e mapper.expr mapper exp]]
+        let warning =
+          str
+            ("let%lwt should not be used at the module item level.\n" ^
+             "Replace let%lwt x = e by let x = Lwt_main.run (e)")
+        in
+        [%stri
+          let [%p var] =
+            (Lwt_main.run [@ocaml.ppwarning [%e warning]])
+              [%e mapper.expr mapper exp]]
           [@metaloc !default_loc]
 
       | x -> default_mapper.structure_item mapper x);

diff --git a/test/ppx_expect/cases/run_1.expect b/test/ppx_expect/cases/run_1.expect
@@ -0,0 +1,3 @@
+File "run_1.ml", line 2, characters 0-26:
+Warning 22: let%lwt should not be used at the module item level.
+Replace let%lwt x = e by let x = Lwt_main.run (e)
diff --git a/test/ppx_expect/cases/run_1.ml b/test/ppx_expect/cases/run_1.ml
@@ -1,2 +1,2 @@
-let%lwt () =
-  Lwt.return ()
+(* On one line for error message compatibility with 4.09. *)
+let%lwt () = Lwt.return ()