add warning when iter_choices return a 3 items tuple

src/wtforms/widgets/core.py

@@ -1,3 +1,5 @@
+import warnings
+
 from markupsafe import escape
 from markupsafe import Markup
 
@@ -362,6 +364,12 @@ def __call__(self, field, **kwargs):
                     if len(choice) == 4:
                         val, label, selected, render_kw = choice
                     else:
+                        warnings.warn(
+                            "'iter_groups' is expected to return 4 items tuple since "
+                            "wtforms 3.1, this will be mandatory in wtforms 3.2",
+                            DeprecationWarning,
+                            stacklevel=2,
+                        )
                         val, label, selected = choice
                         render_kw = {}
                     html.append(self.render_option(val, label, selected, **render_kw))
@@ -371,6 +379,12 @@ def __call__(self, field, **kwargs):
                 if len(choice) == 4:
                     val, label, selected, render_kw = choice
                 else:
+                    warnings.warn(
+                        "'iter_groups' is expected to return 4 items tuple since "
+                        "wtforms 3.1, this will be mandatory in wtforms 3.2",
+                        DeprecationWarning,
+                        stacklevel=2,
+                    )
                     val, label, selected = choice
                     render_kw = {}
                 html.append(self.render_option(val, label, selected, **render_kw))

tests/conftest.py

@@ -25,7 +25,7 @@ def basic_widget_dummy_field(dummy_field_class):
 
 @pytest.fixture
 def select_dummy_field(dummy_field_class):
-    return dummy_field_class([("foo", "lfoo", True), ("bar", "lbar", False)])
+    return dummy_field_class([("foo", "lfoo", True, {}), ("bar", "lbar", False, {})])
 
 
 @pytest.fixture