[webkit-changes] [WebKit/WebKit] 516777: REGRESSION (259904 at main): Gmail App stutters / jit...

[Wenson Hsieh]

  Branch: refs/heads/main
  Home:   https://github.com/WebKit/WebKit
  Commit: 51677708a84b70ea867ffe8810705f094414620e
      https://github.com/WebKit/WebKit/commit/51677708a84b70ea867ffe8810705f094414620e
  Author: Wenson Hsieh <wenson_hsieh at apple.com>
  Date:   2023-04-14 (Fri, 14 Apr 2023)

  Changed paths:
    M Source/WTF/Scripts/Preferences/UnifiedWebPreferences.yaml
    M Source/WTF/wtf/cocoa/RuntimeApplicationChecksCocoa.h
    M Source/WebCore/platform/RuntimeApplicationChecks.h
    M Source/WebCore/platform/cocoa/RuntimeApplicationChecksCocoa.mm
    M Source/WebKit/Shared/WebPreferencesDefaultValues.cpp
    M Source/WebKit/Shared/WebPreferencesDefaultValues.h

  Log Message:
  -----------
  REGRESSION (259904 at main): Gmail App stutters / jitters when scrolling down in compose view
https://bugs.webkit.org/show_bug.cgi?id=255431
rdar://106644805

Reviewed by Ryosuke Niwa.

In the iOS Gmail app when Live Range Selection is enabled by default, the web view used for compose
gets into a state where it constantly modifies the selection without any visual change. This is
because the page installs a `selectionchange` event listener on the document element; when fired,
this event listener creates a new `span` element whose text is a single zero-width joiner character,
and then inserts this node into the selection range via `getSelection().getRangeAt(0).insertNode()`.

When live range selection is enabled, this causes each `selectionchange` event to mutate the
selection, queueing a subsequent `selectionchange` event in the process. Since the event is
scheduled, this doesn't end up being an infinite loop; however, it does lead to various issues, such
as the fact that attempts to scroll the selection off-screen cause the scroll position to stutter as
we scroll to reveal the selection range that is being set every frame.

Fix this by adding a linked-on-or-after check for live range selection. For now, we additionally
limit this to Gmail (currently the only known third-party app to encounter this bincompat issue),
in hopes that we'll be able to remove legacy (non-live-range) code sooner, once the Gmail app adapts
to live ranges.

* Source/WTF/Scripts/Preferences/UnifiedWebPreferences.yaml:
* Source/WTF/wtf/cocoa/RuntimeApplicationChecksCocoa.h:
* Source/WebCore/platform/RuntimeApplicationChecks.h:
* Source/WebCore/platform/cocoa/RuntimeApplicationChecksCocoa.mm:
(WebCore::IOSApplication::isGmail):

Add a new method to check for the Gmail app, so that we can disable Live Range Selection for only
Gmail (until they adjust their injected script to be compatible with our new behavior).

* Source/WebKit/Shared/WebPreferencesDefaultValues.cpp:
(WebKit::defaultLiveRangeSelectionEnabled):
* Source/WebKit/Shared/WebPreferencesDefaultValues.h:

Canonical link: https://commits.webkit.org/262960@main