fix: Clamp character indices when converting a text selection to a range

AccessKit / accesskit

UI accessibility infrastructure across platforms and programming languages

BSD 3-Clause "New" or "Revised" License

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fix: Clamp character indices when converting a text selection to a range #416

Closed mwcampbell closed 1 month ago

mwcampbell commented 1 month ago

@DataTriny discovered a way to cause a panic in AccessKit when moving in an egui multi-line edit. Apparently, the egui cursor can end up being outside the actual bounds of the text. I could fix this in egui, but I think it's better to make AccessKit resilient to broken implementations, when we can do so at little cost. So I implemented a fix in AccessKit instead.

To test this fix with egui, you'll need to cherry-pick this PR onto a local copy of the winit-0.29-backport branch.

DataTriny commented 1 month ago

For reference, here are the steps that would trigger a panic:

Write some text inside an egui multi-line text area,
Add a blank line at the end,
Go back to the line above (up arrow),
Move the caret to the right by at least one character,
Now go down to land on the last blank line.

I can confirm that this PR fixes the bug.