Repository: Textualize/textual

Issue:
RadioButton still selectable by keyboard when disabled
It appears that when a `RadioButton` is disabled, click events no longer respond as expected, but you can still navigate to it with the keyboard and select it with `space` or `enter`.

![radio-select-disabled](https://github.com/Textualize/textual/assets/11033703/d3e8667f-a704-4d22-8692-c30873dd106a)

```python
from textual.app import App, ComposeResult
from textual.widgets import RadioButton, RadioSet, Static


class Test(App):
    DEFAULT_CSS = """
    RadioButton:disabled {
        color: red;
    }
    """

    def compose(self) -> ComposeResult:
        with RadioSet():
            yield RadioButton("Enabled 1")
            yield RadioButton("Disabled 2", disabled=True)
            yield RadioButton("Disabled 3", disabled=True)
        yield Static("Selected:", id="selected")

    def on_radio_set_changed(self, radio_set: RadioSet.Changed) -> None:
        self.query_one("#selected").update(f"Selected: {radio_set.pressed.label}")


if __name__ == "__main__":
    app = Test()
    app.run()
```

# Textual Diagnostics

## Versions

| Name    | Value  |
|---------|--------|
| Textual | 0.44.1 |
| Rich    | 13.7.0 |

## Python

| Name           | Value                                                     |
|----------------|-----------------------------------------------------------|
| Version        | 3.8.10                                                    |
| Implementation | CPython                                                   |
| Compiler       | Clang 12.0.5 (clang-1205.0.22.9)                          |
| Executable     | /Users/geoff/Documents/projects/test/venv/bin/python |

## Operating System

| Name    | Value                                                                                                 |
|---------|-------------------------------------------------------------------------------------------------------|
| System  | Darwin                                                                                                |
| Release | 22.5.0                                                                                                |
| Version | Darwin Kernel Version 22.5.0: Thu Jun  8 22:22:19 PDT 2023; root:xnu-8796.121.3~7/RELEASE_ARM64_T8103 |

## Terminal

| Name                 | Value           |
|----------------------|-----------------|
| Terminal Application | vscode (1.85.0) |
| TERM                 | xterm-256color  |
| COLORTERM            | truecolor       |
| FORCE_COLOR          | *Not set*       |
| NO_COLOR             | *Not set*       |

## Rich Console options

| Name           | Value                |
|----------------|----------------------|
| size           | width=158, height=40 |
| legacy_windows | False                |
| min_width      | 1                    |
| max_width      | 158                  |
| is_terminal    | True                 |
| encoding       | utf-8                |
| max_height     | 40                   |
| justify        | None                 |
| overflow       | None                 |
| no_wrap        | False                |
| highlight      | None                 |
| markup         | None                 |
| height         | None                 |





Discussion:
Good spot: for clarification, this looks to be a `RadioSet` bug, not a `RadioButton` bug.
This may impact other widgets where you can press a key to select. Suggest we also check other widgets.

Resolving patch:
diff --git a/src/textual/widgets/_radio_set.py b/src/textual/widgets/_radio_set.py
--- a/src/textual/widgets/_radio_set.py
+++ b/src/textual/widgets/_radio_set.py
@@ -2,7 +2,8 @@
 
 from __future__ import annotations
 
-from typing import ClassVar, Optional
+from contextlib import suppress
+from typing import ClassVar, Literal, Optional
 
 import rich.repr
 
@@ -151,9 +152,8 @@ def __init__(
     def _on_mount(self, _: Mount) -> None:
         """Perform some processing once mounted in the DOM."""
 
-        # If there are radio buttons, select the first one.
-        if self._nodes:
-            self._selected = 0
+        # If there are radio buttons, select the first available one.
+        self.action_next_button()
 
         # Get all the buttons within us; we'll be doing a couple of things
         # with that list.
@@ -248,24 +248,58 @@ def action_previous_button(self) -> None:
 
         Note that this will wrap around to the end if at the start.
         """
-        if self._nodes:
-            if self._selected == 0:
-                self._selected = len(self.children) - 1
-            elif self._selected is None:
-                self._selected = 0
-            else:
-                self._selected -= 1
+        self._move_selected_button(-1)
 
     def action_next_button(self) -> None:
         """Navigate to the next button in the set.
 
         Note that this will wrap around to the start if at the end.
         """
-        if self._nodes:
-            if self._selected is None or self._selected == len(self._nodes) - 1:
-                self._selected = 0
-            else:
-                self._selected += 1
+        self._move_selected_button(1)
+
+    def _move_selected_button(self, direction: Literal[-1, 1]) -> None:
+        """Move the selected button to the next or previous one.
+
+        Note that this will wrap around the start/end of the button list.
+
+        We compute the available buttons by ignoring the disabled ones and then
+        we induce an ordering by computing the distance to the currently selected one if
+        we start at the selected button and then start moving in the direction indicated.
+
+        For example, if the direction is `1` and self._selected is 2, we have this:
+        selected:     v
+        buttons:  X X X X X X X
+        indices:  0 1 2 3 4 5 6
+        distance: 5 6 0 1 2 3 4
+
+        Args:
+            direction: `1` to move to the next button and `-1` for the previous.
+        """
+
+        candidate_indices = (
+            index
+            for index, button in enumerate(self.children)
+            if not button.disabled and index != self._selected
+        )
+
+        if self._selected is None:
+            with suppress(StopIteration):
+                self._selected = next(candidate_indices)
+        else:
+            selected = self._selected
+
+            def distance(index: int) -> int:
+                """Induce a distance between the given index and the selected button.
+
+                Args:
+                    index: The index of the button to consider.
+
+                Returns:
+                    The distance between the two buttons.
+                """
+                return direction * (index - selected) % len(self.children)
+
+            self._selected = min(candidate_indices, key=distance, default=None)
 
     def action_toggle(self) -> None:
         """Toggle the state of the currently-selected button."""


Test patch:
diff --git a/tests/toggles/test_radioset.py b/tests/toggles/test_radioset.py
--- a/tests/toggles/test_radioset.py
+++ b/tests/toggles/test_radioset.py
@@ -135,3 +135,49 @@ async def test_there_can_only_be_one():
     async with BadRadioSetApp().run_test() as pilot:
         assert len(pilot.app.query("RadioButton.-on")) == 1
         assert pilot.app.query_one(RadioSet).pressed_index == 0
+
+
+class RadioSetDisabledButtonsApp(App[None]):
+    def compose(self) -> ComposeResult:
+        self.selected = []
+        with RadioSet():
+            yield RadioButton("0", disabled=True)
+            yield RadioButton("1")
+            yield RadioButton("2", disabled=True)
+            yield RadioButton("3", disabled=True)
+            yield RadioButton("4")
+            yield RadioButton("5")
+            yield RadioButton("6", disabled=True)
+            yield RadioButton("7")
+            yield RadioButton("8", disabled=True)
+
+    def on_radio_set_changed(self, radio_set: RadioSet.Changed) -> None:
+        self.selected.append(str(radio_set.pressed.label))
+
+
+async def test_keyboard_navigation_with_disabled_buttons():
+    """Regression test for https://github.com/Textualize/textual/issues/3839."""
+
+    app = RadioSetDisabledButtonsApp()
+    async with app.run_test() as pilot:
+        await pilot.press("enter")
+        for _ in range(5):
+            await pilot.press("down")
+            await pilot.press("enter")
+        for _ in range(5):
+            await pilot.press("up")
+            await pilot.press("enter")
+
+    assert app.selected == [
+        "1",
+        "4",
+        "5",
+        "7",
+        "1",
+        "4",
+        "1",
+        "7",
+        "5",
+        "4",
+        "1",
+    ]