Error message when two same states

compiler/desugared/name_resolution.ml

@@ -366,9 +366,29 @@ let process_data_decl
     in
     let states_idmap, states_list =
       List.fold_right
-        (fun state_id (states_idmap, states_list) ->
+        (fun state_id
+             ((states_idmap : StateName.t IdentName.Map.t), states_list) ->
+          let state_id_name = Marked.unmark state_id in
+          if IdentName.Map.mem state_id_name states_idmap then
+            Errors.raise_multispanned_error
+              [
+                ( Some
+                    (Format.asprintf "First instance of state %a:"
+                       (Cli.format_with_style [ANSITerminal.yellow])
+                       ("\"" ^ state_id_name ^ "\"")),
+                  Marked.get_mark state_id );
+                ( Some
+                    (Format.asprintf "Second instance of state %a:"
+                       (Cli.format_with_style [ANSITerminal.yellow])
+                       ("\"" ^ state_id_name ^ "\"")),
+                  Marked.get_mark
+                    (IdentName.Map.find state_id_name states_idmap
+                    |> StateName.get_info) );
+              ]
+              "There are two states with the same name for the same variable: \
+               this is ambiguous. Please change the name of either states.";
           let state_uid = StateName.fresh state_id in
-          ( IdentName.Map.add (Marked.unmark state_id) state_uid states_idmap,
+          ( IdentName.Map.add state_id_name state_uid states_idmap,
             state_uid :: states_list ))
         decl.scope_decl_context_item_states (IdentName.Map.empty, [])
     in

tests/test_scope/good/scope_call3.catala_en

@@ -43,7 +43,7 @@ $ catala Interpret -t -s HousingComputation
      7 │   definition f of x equals (output of RentComputation).f of x
        │                             ‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾
     
-[LOG]     ≔  RentComputation.direct.output: { "f" = λ (param0: integer) → { "f" = λ (x: integer) → error_empty ⟨true ⊢ (λ (x1: integer) → error_empty ⟨true ⊢ x1 +! 1⟩) (x +! 1)⟩ }_RentComputation."f" param0 }_RentComputation
+[LOG]     ≔  RentComputation.direct.output: { "f" = <function>}_RentComputation
 [LOG]   ←  RentComputation.direct
 [LOG]   →  RentComputation.f
 [LOG]     ≔  RentComputation.f.input0: 1

tests/test_variable_state/bad/double_same_state.catala_en

@@ -0,0 +1,31 @@
+## Test
+
+```catala
+declaration scope A:
+  output foo content integer
+    state bar
+    state bar
+
+scope A:
+  definition foo state bar equals 2
+```
+
+```catala-test-inline
+$ catala Typecheck
+[ERROR] There are two states with the same name for the same variable: this is ambiguous. Please change the name of either states.
+
+First instance of state "bar":
+┌─⯈ tests/test_variable_state/bad/double_same_state.catala_en:6.11-6.14:
+└─┐
+6 │     state bar
+  │           ‾‾‾
+  └─ Test
+
+Second instance of state "bar":
+┌─⯈ tests/test_variable_state/bad/double_same_state.catala_en:7.11-7.14:
+└─┐
+7 │     state bar
+  │           ‾‾‾
+  └─ Test
+#return code 255#
+```