[rejected AI] Preserve explicitly empty choice labels

CHANGES.rst

@@ -5,6 +5,7 @@ Version 3.3.0b4
 
 Unreleased
 
+- Preserve explicitly empty labels when rendering select and radio choices.
 - :class:`~datalist.DataList` ``choices`` accepts the shorthand
   ``{value: label}`` dict syntax. :issue:`886`
 - ``choices`` callables on fields nested in a :class:`~fields.FieldList` are

src/wtforms/fields/choices.py

@@ -253,7 +253,7 @@ def __iter__(self):
         for i, choice in enumerate(self._iter_choices_normalized()):
             opt = self._Option(
                 id=f"{self.id}-{i}",
-                label=choice.label or choice.value,
+                label=choice.value if choice.label is None else choice.label,
                 **opts,
             )
             opt.choice = choice

src/wtforms/widgets/core.py

@@ -448,7 +448,7 @@ def render_option(cls, choice, **kwargs):
         options = {"value": value, **(choice.render_kw or {}), **kwargs}
         if choice.selected:
             options["selected"] = True
-        label = escape(choice.label or choice.value)
+        label = escape(choice.value if choice.label is None else choice.label)
         return Markup(f"<option {html_params(**options)}>{label}</option>")
 
     @classmethod
@@ -482,7 +482,8 @@ def _dispatch_render_option(cls):
         accepts_kwargs = any(p.kind == p.VAR_KEYWORD for p in sig.parameters.values())
 
         def adapter(choice):
-            args = (choice.value, choice.label or choice.value, choice.selected)
+            label = choice.value if choice.label is None else choice.label
+            args = (choice.value, label, choice.selected)
             if accepts_kwargs:
                 return ro(*args, **(choice.render_kw or {}))
             return ro(*args)

tests/fields/test_select.py

@@ -11,8 +11,10 @@
 from wtforms.fields import enum_choices
 from wtforms.fields import enum_coerce
 from wtforms.fields import Field
+from wtforms.fields import RadioField
 from wtforms.fields import SelectChoice
 from wtforms.fields import SelectField
+from wtforms.fields import SelectMultipleField
 from wtforms.form import Form
 
 if sys.version_info >= (3, 11):
@@ -25,6 +27,46 @@ def make_form(name="F", **fields):
     return type(str(name), (Form,), fields)
 
 
+@pytest.mark.parametrize("field_type", [SelectField, SelectMultipleField, RadioField])
+@pytest.mark.parametrize("optgroup", [None, "Group"])
+def test_explicit_empty_choice_labels(field_type, optgroup):
+    F = make_form(
+        s=field_type(
+            choices=[
+                SelectChoice("blank", "", optgroup=optgroup),
+                SelectChoice("automatic", optgroup=optgroup),
+            ]
+        )
+    )
+    form = F(s=["blank"] if field_type is SelectMultipleField else "blank")
+    options = list(form.s)
+    assert options[0].label.text == ""
+    assert options[1].label.text == "automatic"
+    if field_type is RadioField:
+        assert '<label for="s-0"></label>' in form.s()
+    else:
+        assert '<option selected value="blank"></option>' in form.s()
+        assert '<option value="automatic">automatic</option>' in form.s()
+
+
+def test_legacy_render_option_preserves_empty_label():
+    labels = []
+
+    class LegacySelect(widgets.Select):
+        @classmethod
+        def render_option(cls, value, label, selected, **kwargs):
+            labels.append(label)
+            return super().render_option(Choice(value, label, selected, kwargs))
+
+    F = make_form(
+        s=SelectField(choices=[SelectChoice("blank", "")], widget=LegacySelect())
+    )
+    with pytest.warns(DeprecationWarning, match="pre-3.3 signature"):
+        html = F(s="blank").s()
+    assert labels == [""]
+    assert '<option selected value="blank"></option>' in html
+
+
 def test_select_field_copies_choices():
     class F(Form):
         items = SelectField(choices=[])