iOS Text Editing Infinite Loop

[justinmc]

Description

Programmatically modifying text while it is being input causes an infinite loop on iOS, but not on Android.

For example, this is reproduced when setting an onChanged handler and adding a character to the text. See the linked issue for more details.

The reason why Android doesn't cause an infinite loop is that Android batches text changes that come very quickly. This PR solves the problem on iOS by performing a similar batching by debouncing. eliminating the ACK response that the engine was sending back to the framework.

Related Issues

Closes flutter/flutter#61282

Further work in this area:
#21534
flutter/flutter#66864

Tests

I added the following tests:

• Updated tests that depended on the ACK response.

Breaking Change

Not a breaking change.

[LongCatIsLooong]

We reuse FlutterTextInputView so the cache needs to be erased every time the connection changes/resets. Also this needs to be properly deallocated I think.

[justinmc]

Alright got the deallocation in 9949623. For erasing the state each time the connection changes, would that just be in resetAllClientIds?

[LongCatIsLooong]

FlutterTextInputView.setClientId I think?

[LongCatIsLooong]

Is possible to fix this by holding off the framework -> engine TextEditingValue update until onChange is called? Or there're other manifestations of this bug (other than changing the text editing value in onChange)?

[justinmc]

@LongCatIsLooong Good thinking. I just tried playing around with that idea and it didn't seem to work, though (messing with the calls around here).

The reason it doesn't work seems to be that the problem is more with the engine sending updates to the framework too fast. Here's an example:

• Framework receives "a" from the engine, changes it to "a0", and sends it back to the engine.
• Framework receives "ab" from the engine before the "a0" ack because the typing was so fast. It changes it to "ab0" and sends that to the engine.
• Framework receives the engine's ack of its first message, "a0". Comparing that to its latest value, "ab0", it concludes that it needs to call onChanged and another zero is added and sent to the engine: "a00".
• Framework receives the engine's ack of its second message, "ab0", calls onChanged and sends the engine "ab00".
• Infinite loop where messages alternate between "a000..." and "ab000..." with increasing zeroes.

Maybe this could be fixed in the framework with a similar sort of batching that is being done in the engine in this PR, or a more sophisticated queue that waits for ack responses from the engine?