Edition compte user: améliore message erreur si cas_id dupliqué

app/auth/models.py

@@ -67,14 +67,6 @@ def is_valid_user_name(user_name: str) -> bool:
     )
 
 
-def is_new_cas_id(cas_id: str) -> bool:
-    "Check that cas_id is a valid new id (uniqueness, allow nulls)"
-    if not cas_id:
-        return True
-    nb_with_this_id = db.session.query(User).filter_by(cas_id=cas_id).count()
-    return nb_with_this_id == 0
-
-
 class User(UserMixin, ScoDocModel):
     """ScoDoc users, handled by Flask / SQLAlchemy"""
 
@@ -435,11 +427,18 @@ class User(UserMixin, ScoDocModel):
                 if cas_id:
                     new_cas_id = cas_id
         if new_cas_id != self.cas_id:
-            if is_new_cas_id(new_cas_id):
+            existing: User = (
+                db.session.query(User).filter_by(cas_id=new_cas_id).first()
+                if new_cas_id is not None
+                else None
+            )
+            if not existing:
                 self.cas_id = new_cas_id
             else:
-                log(f"User.from_dict: CAS id invalide pour {self.user_name}")
-                raise ScoValueError(f"CAS id invalide pour {self.user_name}")
+                msg = f"""CAS id invalide pour {self.user_name
+                    }, déjà utilisé par {existing.user_name}"""
+                log(f"User.from_dict: {msg}")
+                raise ScoValueError(msg)
 
     def get_token(self, expires_in=3600):
         "Un jeton pour cet user. Stocké en base, non commité."