chunhtai 26037dff87
Add set semantics enabled API and wire iOS a11y bridge (#161265)
fixes https://github.com/flutter/flutter/issues/158399

old pr https://github.com/flutter/engine/pull/56691

previously the only correct way to enable semantics is that ios
embedding receive signal from native OS, it call SetSemanticsEnabled to
shell and then to dart to enable semantics tree generation.

If for some reason framework decide to enable semantics first, e.g.
through SemanticsBinding.instance.ensureSemantics(typically due to
integration test or ci that wants to test semantics), the update will be
dropped in shell. Even if it later on receive signal from native OS to
turn on semantics, it can't construct the complete accessibility tree in
embedding because the updatesemantics sends diff update and previous
updates are gone forever. It will end up in a broken state.

This pr changes so that the only source of truth will be in the
framework side. When framework starts generating the the semantics tree,
it will call SetSemanticsTreeEnabled through dart:ui, and the embedding
needs to prepare itself to accept semantics update after receiving the
message.

This however require some refactoring on iOS embedding because it will
only create a11y bridge when receiving OS notification when assitive
technologies turns on.

This requires three phase transition

add an empty dart:ui API setSemanticsTreeEnabled
makes framework calls the empty API.
merge this pr with actual implementation of setSemanticsTreeEnabled

I will do the android part in a separate pr


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2025-03-24 20:11:13 +00:00
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