Better error message

compiler/surface/name_resolution.ml

@@ -28,6 +28,7 @@ type unique_rulename = Ambiguous of Pos.t list | Unique of Desugared.Ast.RuleNam
 type scope_context = {
   var_idmap : Scopelang.Ast.ScopeVar.t Desugared.Ast.IdentMap.t;  (** Scope variables *)
   label_idmap : Desugared.Ast.RuleName.t Desugared.Ast.IdentMap.t;
+      (** Set of rules attached to a label *)
   default_rulemap : unique_rulename Desugared.Ast.ScopeDefMap.t;
       (** What is the default rule to refer to for unnamed exceptions, if any *)
   sub_scopes_idmap : Scopelang.Ast.SubScopeName.t Desugared.Ast.IdentMap.t;
@@ -460,8 +461,8 @@ let process_definition (ctxt : context) (s_name : Scopelang.Ast.ScopeName.t) (d
                     match Desugared.Ast.IdentMap.find_opt (Pos.unmark label) s_ctxt.label_idmap with
                     | Some existing_label ->
                         Errors.raise_multispanned_error
-                          "This label has already been given to a rule defining this variable, \
-                           please pick a new one."
+                          "This label has already been given to another rule, please pick a new \
+                           one since labels should be unique."
                           [
                             (Some "Duplicate label:", Pos.get_position label);
                             ( Some "Existing rule with same label:",

tests/test_exception/bad/output/duplicate_labels.catala_en.A.out

@@ -1,4 +1,4 @@
-[ERROR] This label has already been given to a rule defining this variable, please pick a new one.
+[ERROR] This label has already been given to another rule, please pick a new one since labels should be unique.
 
 Duplicate label:
   --> test_exception/bad/duplicate_labels.catala_en

tests/test_exception/bad/output/same_label_two_variables.catala_en.A.out

@@ -0,0 +1,17 @@
+[ERROR] This label has already been given to another rule, please pick a new one since labels should be unique.
+
+Duplicate label:
+  --> test_exception/bad/same_label_two_variables.catala_en
+   | 
+13 |   label base
+   |         ^^^^
+   + Test
+
+Existing rule with same label:
+  --> test_exception/bad/same_label_two_variables.catala_en
+   | 
+10 |   label base
+   |   ^^^^^^^^^
+11 |   definition x equals -1
+   |   ^^^^^^^^^^^^^^^^^^^^^^^
+   + 

tests/test_exception/bad/same_label_two_variables.catala_en

@@ -0,0 +1,20 @@
+## Test
+
+```catala
+declaration scope A:
+  context x content integer
+  context y content integer
+  context z content integer
+
+scope A:
+  label base
+  definition x equals -1
+
+  label base
+  definition y equals 1
+
+  exception base
+  definition x under condition z = 0 consequence equals 0
+
+  definition z equals 0
+```