Option indexing appears to break after an OptionList.clear_options and OptionList.add_option(s)

[davep]

This looks to be a bug introduced in v0.48 of Textual. Consider this code:

from textual import on
from textual.app import App, ComposeResult
from textual.reactive import var
from textual.widgets import Button, OptionList
from textual.widgets.option_list import Option

class OptionListReAdd(App[None]):

    count: var[int] = var(0)

    def compose(self) -> ComposeResult:
        yield Button("Add again")
        yield OptionList(Option(f"This is the option we'll keep adding {self.count}", id="0"))

    @on(Button.Pressed)
    def readd(self) -> None:
        self.count += 1
        _ = self.query_one(OptionList).get_option("0")
        self.query_one(OptionList).clear_options().add_option(
            Option(f"This is the option we'll keep adding {self.count}", id="0")
        )

if __name__ == "__main__":
    OptionListReAdd().run()

With v0.47.1, you can press the button many times and the code does what you'd expect; the option keeps being replaced, and it can always be acquired back with a get_option on its ID.

With v0.48.0/1 you get the following error the second time you press the button:

╭────────────────────────────────────────────────────── Traceback (most recent call last) ───────────────────────────────────────────────────────╮
│ /Users/davep/develop/python/textual-sandbox/option_list_readd.py:18 in readd                                                                   │
│                                                                                                                                                │
│   15 │   @on(Button.Pressed)                                                                                                                   │
│   16 │   def readd(self) -> None:                                                                                                              │
│   17 │   │   self.count += 1                                                                                                                   │
│ ❱ 18 │   │   _ = self.query_one(OptionList).get_option("0")                                                                                    │
│   19 │   │   self.query_one(OptionList).clear_options().add_option(                                                                            │
│   20 │   │   │   Option(f"This is the option we'll keep adding {self.count}", id="0")                                                          │
│   21 │   │   )                                                                                                                                 │
│                                                                                                                                                │
│ ╭──────────────────────────────── locals ─────────────────────────────────╮                                                                    │
│ │ self = OptionListReAdd(title='OptionListReAdd', classes={'-dark-mode'}) │                                                                    │
│ ╰─────────────────────────────────────────────────────────────────────────╯                                                                    │
│                                                                                                                                                │
│ /Users/davep/develop/python/textual-sandbox/.venv/lib/python3.10/site-packages/textual/widgets/_option_list.py:861 in get_option               │
│                                                                                                                                                │
│    858 │   │   Raises:                                                                          ╭───────── locals ─────────╮                   │
│    859 │   │   │   OptionDoesNotExist: If no option has the given ID.                           │ option_id = '0'          │                   │
│    860 │   │   """                                                                              │      self = OptionList() │                   │
│ ❱  861 │   │   return self.get_option_at_index(self.get_option_index(option_id))                ╰──────────────────────────╯                   │
│    862 │                                                                                                                                       │
│    863 │   def get_option_index(self, option_id: str) -> int:                                                                                  │
│    864 │   │   """Get the index of the option with the given ID.                                                                               │
│                                                                                                                                                │
│ /Users/davep/develop/python/textual-sandbox/.venv/lib/python3.10/site-packages/textual/widgets/_option_list.py:845 in get_option_at_index      │
│                                                                                                                                                │
│    842 │   │   try:                                                                             ╭─────── locals ───────╮                       │
│    843 │   │   │   return self._options[index]                                                  │ index = 1            │                       │
│    844 │   │   except IndexError:                                                               │  self = OptionList() │                       │
│ ❱  845 │   │   │   raise OptionDoesNotExist(                                                    ╰──────────────────────╯                       │
│    846 │   │   │   │   f"There is no option with an index of {index}"                                                                          │
│    847 │   │   │   ) from None                                                                                                                 │
│    848                                                                                                                                         │
╰────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────╯
OptionDoesNotExist: There is no option with an index of 1

Tagging @willmcgugan for triage.

Perhaps related to b1aaea7

[davep]

Diving into the innards with this:

from textual import on
from textual.app import App, ComposeResult
from textual.containers import Horizontal
from textual.reactive import var
from textual.widgets import Button, OptionList, Pretty
from textual.widgets.option_list import Option

class OptionListReAdd(App[None]):

    CSS = """
    OptionList {
        height: 1fr;
    }

    Horizontal {
        height: 2fr;
        Pretty {
            width: 1fr;
        }
    }
    """

    count: var[int] = var(0)

    def compose(self) -> ComposeResult:
        yield Button("Add again")
        yield OptionList()
        with Horizontal():
            yield Pretty([], id="options")
            yield Pretty([], id="ids")

    @on(Button.Pressed)
    def readd(self) -> None:
        self.count += 1
        self.query_one(OptionList).add_option(
            Option(f"Option {self.count}", id=str(self.count))
        )
        self.query_one("#options", Pretty).update(
            self.query_one(OptionList)._options
        )
        self.query_one("#ids", Pretty).update(
            self.query_one(OptionList)._option_ids
        )

if __name__ == "__main__":
    OptionListReAdd().run()

I see this:

it looks like the changes made have introduced some sort of off-by-one error on the index mapping for each ID.

[davep]

It's a bit late in the evening for me to do a PR with confidence, but it looks like the issue is fixed with something like this:

diff --git a/src/textual/widgets/_option_list.py b/src/textual/widgets/_option_list.py
index 59e2adf9..9366f071 100644
--- a/src/textual/widgets/_option_list.py
+++ b/src/textual/widgets/_option_list.py
@@ -596,13 +596,14 @@ class OptionList(ScrollView, can_focus=True):
             # Turn any incoming values into valid content for the list.
             content = [self._make_content(item) for item in items]
             self._duplicate_id_check(content)
+            start = len(self._options)
             self._contents.extend(content)
             # Pull out the content that is genuine options. Add them to the
             # list of options and map option IDs to their new indices.
             new_options = [item for item in content if isinstance(item, Option)]
             self._options.extend(new_options)
             for new_option_index, new_option in enumerate(
-                new_options, start=len(self._options)
+                new_options, start=start
             ):
                 if new_option.id:
                     self._option_ids[new_option.id] = new_option_index

The calculation of the new index values for the mapping is currently starting after the new options have been added, when it should go from the last position before they're added (is how it looks to me).

Pinging @rodrigogiraoserrao for a double-check as this does seem to be from b1aaea7

[davep]

A test like this illustrates the issue:

from textual.app import App, ComposeResult
from textual.widgets import OptionList
from textual.widgets.option_list import Option

class OptionListApp(App[None]):
    """Test option list application."""

    def compose(self) -> ComposeResult:
        yield OptionList()

async def test_get_after_add() -> None:
    """It should be possible to get an option by ID after adding."""
    async with OptionListApp().run_test() as pilot:
        option_list = pilot.app.query_one(OptionList)
        option_list.add_option(Option("0", id="0"))
        assert option_list.get_option("0").id == "0"

This will fail.

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