AX: Bound all indefinite-blocking main-thread retrieval calls from the accessibility thread with timeouts

[twilco]

ab00c2f

AX: Bound all indefinite-blocking main-thread retrieval calls from the accessibility thread with timeouts
https://bugs.webkit.org/show_bug.cgi?id=314367
rdar://176524311

Reviewed by Dominic Mazzoni.

retrieveAutoreleasedValueFromMainThread and retrieveValueFromMainThread block
the AX thread forever via callOnMainThreadAndWait if the main thread is busy
(e.g. long-running JS, layout, synchronous IPC). This can cause assistive
technologies to hang waiting for responses that never come.

Convert all unguarded call sites in WebAccessibilityObjectWrapperMac to use
retrieveValueFromMainThreadWithTimeout (or the WithDefault variant), returning
nil on timeout.

For three operations (text marker for position, start/end text marker for
bounds), add approximate-hit-test fallbacks: when the main thread times out,
use AXIsolatedObject::approximateHitTest to find the element at the relevant
point and return the start/end of its text marker range. This provides a
potentially less accurate, but usable result rather than nothing.

Make AXIsolatedObject::approximateHitTest public so the wrapper can call it
directly for these fallbacks without going through accessibilityHitTest (which
would redundantly attempt the main thread again).

* Source/WebCore/accessibility/AXCoreObject.h:
* Source/WebCore/accessibility/isolatedtree/AXIsolatedObject.h:
* Source/WebCore/accessibility/mac/WebAccessibilityObjectWrapperMac.mm:
(-[WebAccessibilityObjectWrapper attachmentView]):
(-[WebAccessibilityObjectWrapper _associatedPluginParentWith:]):
(handleLineRectsAndTextAttribute):
(-[WebAccessibilityObjectWrapper _accessibilityHitTest:returnPlatformElements:]):
(handleSelectTextWithCriteriaAttribute):
(handleSearchTextWithCriteriaAttribute):
(handleTextOperationAttribute):
(handleEndTextMarkerForBoundsAttribute):
(handleStartTextMarkerForBoundsAttribute):
(handleMisspellingTextMarkerRangeAttribute):
(handleTextMarkerForPositionAttribute):

Canonical link: https://commits.webkit.org/312880@main

60729d3

Misc	iOS, visionOS, tvOS & watchOS	macOS	Linux	Windows	Apple Internal
✅ 🧪 style	✅ 🛠 ios	✅ 🛠 mac	✅ 🛠 wpe	🛠 win	⏳ 🛠 ios-apple
✅ 🧪 bindings	✅ 🛠 ios-sim	✅ 🛠 mac-AS-debug	✅ 🧪 wpe-wk2	🧪 win-tests	⏳ 🛠 mac-apple
✅ 🧪 webkitperl	✅ 🧪 ios-wk2	✅ 🧪 api-mac	✅ 🧪 api-wpe		⏳ 🛠 vision-apple
	✅ 🧪 ios-wk2-wpt	✅ 🧪 api-mac-debug	✅ 🛠 gtk3-libwebrtc
	✅ 🧪 api-ios	✅ 🧪 mac-wk1	✅ 🛠 gtk
	✅ 🛠 ios-safer-cpp	✅ 🧪 mac-wk2	✅ 🧪 gtk-wk2
	✅ 🛠 vision	✅ 🧪 mac-AS-debug-wk2	✅ 🧪 api-gtk
✅ 🛠 🧪 merge	✅ 🛠 vision-sim	✅ 🧪 mac-wk2-stress	✅ 🛠 playstation
	✅ 🧪 vision-wk2	🧪 mac-intel-wk2
	✅ 🛠 tv	✅ 🛠 mac-safer-cpp
	✅ 🛠 tv-sim
	✅ 🛠 watch
	✅ 🛠 watch-sim

[webkit-early-warning-system]

EWS run on current version of this PR (hash 60729d3)

Details

Misc	iOS, visionOS, tvOS & watchOS	macOS	Linux	Windows	Apple Internal
✅ 🧪 style	✅ 🛠 ios	✅ 🛠 mac	✅ 🛠 wpe	🛠 win	⏳ 🛠 ios-apple
✅ 🧪 bindings	✅ 🛠 ios-sim	✅ 🛠 mac-AS-debug	✅ 🧪 wpe-wk2	🧪 win-tests	⏳ 🛠 mac-apple
✅ 🧪 webkitperl	✅ 🧪 ios-wk2	✅ 🧪 api-mac	✅ 🧪 api-wpe		⏳ 🛠 vision-apple
	✅ 🧪 ios-wk2-wpt	✅ 🧪 api-mac-debug	✅ 🛠 gtk3-libwebrtc
	✅ 🧪 api-ios	✅ 🧪 mac-wk1	✅ 🛠 gtk
	✅ 🛠 ios-safer-cpp	✅ 🧪 mac-wk2	✅ 🧪 gtk-wk2
	✅ 🛠 vision	✅ 🧪 mac-AS-debug-wk2	✅ 🧪 api-gtk
✅ 🛠 🧪 merge	✅ 🛠 vision-sim	✅ 🧪 mac-wk2-stress	✅ 🛠 playstation
	✅ 🧪 vision-wk2	🧪 mac-intel-wk2
	✅ 🛠 tv	✅ 🛠 mac-safer-cpp
	✅ 🛠 tv-sim
	✅ 🛠 watch
	✅ 🛠 watch-sim

[webkit-commit-queue]

Committed 312880@main (ab00c2f): https://commits.webkit.org/312880@main

Reviewed commits have been landed. Closing PR #64519 and removing active labels.