fix: fix literal with widgeT_type (#586)

src/magicgui/type_map/_type_map.py

@@ -93,14 +93,8 @@ def match_type(type_: Any, default: Any | None = None) -> WidgetTuple | None:
         return widgets.FunctionGui, {"function": default}
 
     origin = get_origin(type_) or type_
-    if origin is Literal:
-        choices = []
-        nullable = False
-        for choice in get_args(type_):
-            if choice is None:
-                nullable = True
-            else:
-                choices.append(choice)
+    choices, nullable = _literal_choices(type_)
+    if choices is not None:  # it's a Literal type
         return widgets.ComboBox, {"choices": choices, "nullable": nullable}
 
     # sequence of paths
@@ -193,6 +187,24 @@ def _type_optional(
     return type_, nullable
 
 
+def _literal_choices(annotation: Any) -> tuple[list | None, bool]:
+    """Return choices and nullable for a Literal type.
+
+    if annotation is not a Literal type, returns (None, False)
+    """
+    origin = get_origin(annotation) or annotation
+    choices: list | None = None
+    nullable = False
+    if origin is Literal:
+        choices = []
+        for choice in get_args(annotation):
+            if choice is None:
+                nullable = True
+            else:
+                choices.append(choice)
+    return choices, nullable
+
+
 def _pick_widget_type(
     value: Any = Undefined,
     annotation: Any = Undefined,
@@ -219,6 +231,10 @@ def _pick_widget_type(
     _type, optional = _type_optional(value, annotation)
     options.setdefault("nullable", optional)
     choices = choices or (isinstance(_type, EnumMeta) and _type)
+    literal_choices, nullable = _literal_choices(annotation)
+    if literal_choices is not None:
+        choices = literal_choices
+        options["nullable"] = nullable
 
     if "widget_type" in options:
         widget_type = options.pop("widget_type")

tests/test_types.py

@@ -187,3 +187,13 @@ def test_type_registered_warns():
             register_type(Path, widget_type=widgets.TextEdit)
             assert isinstance(widgets.create_widget(annotation=Path), widgets.TextEdit)
     assert isinstance(widgets.create_widget(annotation=Path), widgets.FileEdit)
+
+
+def test_pick_widget_literal():
+    from typing import Literal
+
+    cls, options = type_map.get_widget_class(
+        annotation=Annotated[Literal["a", "b"], {"widget_type": "RadioButtons"}]
+    )
+    assert cls == widgets.RadioButtons
+    assert set(options["choices"]) == {"a", "b"}