Fill generated switch cases with %todo instead of the removed failwith

analysis/src/codemod.ml

@@ -21,7 +21,7 @@ let transform_opt ~source ~pos ~debug ~typ ~hint =
         let cases =
           collect_patterns pattern
           |> List.map (fun (p : Parsetree.pattern) ->
-              Ast_helper.Exp.case p (Type_utils.Codegen.mk_fail_with_exp ()))
+              Ast_helper.Exp.case p (Type_utils.Codegen.mk_todo_exp ()))
         in
         let result = ref None in
         let mk_iterator ~pos ~result =

analysis/src/type_utils.ml

@@ -1035,10 +1035,10 @@ let rec context_path_from_core_type (core_type : Parsetree.core_type) =
   | _ -> None
 
 module Codegen = struct
-  let mk_fail_with_exp () =
-    Ast_helper.Exp.apply
-      (Ast_helper.Exp.ident {txt = Lident "failwith"; loc = Location.none})
-      [(Nolabel, Ast_helper.Exp.constant (Ast_helper.Const.string "TODO"))]
+  (* Placeholder body for generated cases: `%todo`, which compiles (with a
+     warning) and throws at runtime. *)
+  let mk_todo_exp () =
+    Ast_helper.Exp.extension ({txt = "todo"; loc = Location.none}, PStr [])
 
   let mk_construct_pat ?payload name =
     Ast_helper.Pat.construct
@@ -1160,7 +1160,7 @@ module Codegen = struct
       Some
         (patterns
         |> List.map (fun (pat : Parsetree.pattern) ->
-            Ast_helper.Exp.case pat (mk_fail_with_exp ())))
+            Ast_helper.Exp.case pat (mk_todo_exp ())))
 end
 
 let get_module_path_relative_to_env ~debug ~(env : Query_env.t) ~env_from_item

changes/code-action-todo-placeholder.fix.md

@@ -0,0 +1 @@
+- Fill cases added by the exhaustive-switch and add-missing-cases code actions with `%todo` instead of the removed `failwith("TODO")`.

changes/deprecated-let-without-interface.fix.md

@@ -1 +1 @@
-- Warn when another module uses a `@deprecated` `let` binding from a module without an interface file. As a result, `failwith` and `invalid_arg`, deprecated since v12, now emit their deprecation warning when used.
+- Warn when another module uses a `@deprecated` `let` binding from a module without an interface file.

tests/analysis_tests/tests/src/expected/Codemod.res.txt

@@ -2,7 +2,7 @@ Codemod AddMissingCasessrc/Codemod.res 3:10
 switch (v1, v2) {
           //      ^c-a (#valid, #valid) | (#invalid, _)
           | (#valid, #invalid) => ()
-          | (#valid, #valid) => failwith("TODO")
-          | (#invalid, _) => failwith("TODO")
+          | (#valid, #valid) => %todo
+          | (#invalid, _) => %todo
           }
 

tests/analysis_tests/tests/src/expected/ExhaustiveSwitch.res.txt

@@ -128,9 +128,9 @@ TextDocumentEdit: ExhaustiveSwitch.res
 newText:
    <--here
    switch x->getV {
-   | One => failwith("TODO")
-   | Two => failwith("TODO")
-   | Three(_) => failwith("TODO")
+   | One => %todo
+   | Two => %todo
+   | Three(_) => %todo
    }
 
 Xform src/ExhaustiveSwitch.res 36:4
@@ -152,11 +152,11 @@ TextDocumentEdit: ExhaustiveSwitch.res
 newText:
    <--here
    switch vvv {
-   | None => failwith("TODO")
-   | Some(_) => failwith("TODO")
-   | Some(One) => failwith("TODO")
-   | Some(Two) => failwith("TODO")
-   | Some(Three(_)) => failwith("TODO")
+   | None => %todo
+   | Some(_) => %todo
+   | Some(One) => %todo
+   | Some(Two) => %todo
+   | Some(Three(_)) => %todo
    }