prefix unused

Author: zth

compiler/ml/cmt_utils.ml

@@ -10,6 +10,8 @@ type action_type =
   | RewriteObjectToRecord
   | RewriteArrayToTuple
   | RewriteIdent of {new_ident: Longident.t}
+  | PrefixVariableWithUnderscore
+  | RemoveUnusedVariable
 
 type cmt_action = {loc: Location.t; action: action_type; description: string}
 
@@ -23,6 +25,19 @@ let emit_possible_actions_from_warning loc w =
   | Unused_match | Unreachable_case ->
     add_possible_action
       {loc; action = RemoveSwitchCase; description = "Remove switch case"}
+  | Unused_var _ | Unused_var_strict _ ->
+    add_possible_action
+      {
+        loc;
+        action = PrefixVariableWithUnderscore;
+        description = "Prefix with `_`";
+      };
+    add_possible_action
+      {
+        loc;
+        action = RemoveUnusedVariable;
+        description = "Remove unused variable";
+      }
   | _ -> ()
 
 let _ =

tests/build_tests/actions/expected/Actions_PrefixUnusedVarUnderscore_applied.res

@@ -0,0 +1,4 @@
+let f = () => {
+  let _x = 1
+  12
+}

tests/build_tests/actions/fixtures/Actions_PrefixUnusedVarUnderscore.res

@@ -0,0 +1,4 @@
+let f = () => {
+  let x = 1
+  12
+}

tools/src/tools.ml

@@ -1319,6 +1319,33 @@ module Actions = struct
                      | _ -> Some str_item)
             in
             Ast_mapper.default_mapper.structure mapper items);
+        value_bindings =
+          (fun mapper bindings ->
+            (* TODO: Implement removing binding action *)
+            Ast_mapper.default_mapper.value_bindings mapper bindings);
+        pat =
+          (fun mapper pattern ->
+            let pattern =
+              match pattern.ppat_desc with
+              | Ppat_var var -> (
+                let prefix_underscore_action =
+                  actions
+                  |> List.find_opt (fun (action : Cmt_utils.cmt_action) ->
+                         match action.action with
+                         | PrefixVariableWithUnderscore ->
+                           action.loc = pattern.ppat_loc
+                         | _ -> false)
+                in
+                match prefix_underscore_action with
+                | Some _ ->
+                  {
+                    pattern with
+                    ppat_desc = Ppat_var {var with txt = "_" ^ var.txt};
+                  }
+                | None -> pattern)
+              | _ -> pattern
+            in
+            Ast_mapper.default_mapper.pat mapper pattern);
         cases =
           (fun mapper cases ->
             let cases =