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…#30704)

* iOS Background Platform Channels (#29665) * added test that passes before this change, and fails after it * started supporting backwards compatible usage of setting handlers

Fixes an issue with Korean IMEs wherein a text input state update may be sent to the framework that misleads the framework into assuming that IME composing has ended. When inputting Korean text, characters are built up keystroke by keystroke until the point that either: * the user presses space/enter to terminate composing and commit the character, or; * the user presses a key such that the character currently being composed cannot be modified further, and the IME determines that the user has begun composing the next character. The following is an example sequence of events for the latter case: 1. User presses ㅂ. GCS_COMPSTR event received with ㅂ. Embedder sends state update to framework. 2. User presses ㅏ. GCS_COMPSTR event received with 바. Embedder sends state update to framework. 3. User presses ㄴ. GCS_COMPSTR event received with 반. Embedder sends state update to framework. 4. User presses ㅏ. At this point, the current character being composed (반) cannot be modified in a meaningful way, and the IME determines that the user is typing 바 followed by 나. GCS_RESULTSTR event received with 바, immediately followed by GCS_COMPSTR event with 나. In step 4, we previously sent two events to the framework, one immediately after the other: * GCS_RESULTSTR triggers the text input model to commit the current composing region to the string under edit. This causes the composing region to collapse to an empty range. * GCS_COMPSTR triggers the text input model to insert the new composing character and set the composing region to that character. Conceptually, this is an atomic operation. The fourth keystroke causes the 반 character to be broken into two (바 and ㄴ) and the latter to be modified to 나. From the user's point of view, as well as from the IME's point of view, the user has NOT stopped composing, and the composing region has simply moved on to the next character. Flutter has no concept of whether the user is composing or not other that whether a non-empty composing region exists. As such, sending a state update after the GCS_RESULTSTR event misleads the framework into believing that composing has ended. This triggers a serious bug: Text fields with input formatters applied do not perform input formatting updates while composing is active; instead they wait until composing has ended to apply any formatting. The previous behaviour would thus trigger input formatters to be applied each time the user input caused a new character to be input. This has the add-on negative effect that once formatting has been applied, it sends an update back to the embedder so that the native OS text input state can be updated. However, since the GCS_RESULTSTR event is _immediately_ followed by a GCS_COMPSTR, the state has changed in the meantime, and the embedder is left processing an update (the intermediate state sent after the GCS_RESULTSTR) which is now out of date (i.e. missing the new state from the GCS_COMPSTR event). Since GCS_RESULTR events are always immediately followed by a subsequent GCS_COMPSTR (in the case where composing continues) or a WM_IME_ENDCOMPOSITION (in the case where composing is finished), and because the event handlers for both of those send updated state to the framework, this change eliminates sending the (intermediate) state in response to GCS_COMPSTR events. Issue: flutter/flutter#96209 (full fix) Issue: flutter/flutter#88645 (partial fix)

* Use the correct Settings in Engine::Spawn * Add unit tests

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Commits on Jan 12, 2022

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