fix(selection list): update indexes after option removed (#4464)

* fix(selection list): update indexes after option removed * add basic test * update changelog * improve test --------- Co-authored-by: Darren Burns <[email protected]>
Textualize · May 2, 2024 · 17e975d · 17e975d
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diff --git a/CHANGELOG.md b/CHANGELOG.md
@@ -9,15 +9,13 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 
 ### Fixed
 
+- Fixed `SelectionList` issues after removing an option https://github.com/Textualize/textual/pull/4464
 - Fixed `ListView` bugs with the initial index https://github.com/Textualize/textual/pull/4452
 
-## Unreleased
-
 ### Changed
 
 - When displaying a message using `App.exit()`, the console no longer highlights things such as numbers.
 
-
 ## [0.58.1] - 2024-05-01
 
 ### Fixed

diff --git a/src/textual/widgets/_selection_list.py b/src/textual/widgets/_selection_list.py
@@ -646,6 +646,11 @@ def _remove_option(self, index: int) -> None:
         option = self.get_option_at_index(index)
         self._deselect(option.value)
         del self._values[option.value]
+        # Decrement index of options after the one we just removed.
+        self._values = {
+            option_value: option_index - 1 if option_index > index else option_index
+            for option_value, option_index in self._values.items()
+        }
         return super()._remove_option(index)
 
     def add_options(

diff --git a/tests/selection_list/test_selection_list_create.py b/tests/selection_list/test_selection_list_create.py
@@ -114,3 +114,12 @@ async def test_options_are_available_soon() -> None:
     selection = Selection("", 0, id="some_id")
     selection_list = SelectionList[int](selection)
     assert selection_list.get_option("some_id") is selection
+
+
+async def test_removing_option_updates_indexes() -> None:
+    async with SelectionListApp().run_test() as pilot:
+        selections = pilot.app.query_one(SelectionList)
+        assert selections._values == {n: n for n in range(5)}
+
+        selections.remove_option_at_index(0)
+        assert selections._values == {n + 1: n for n in range(4)}