[webkit-changes] [WebKit/WebKit] fdc295: MobileMail sometimes crashes underneath -[WKConten...

[Wenson Hsieh]

  Branch: refs/heads/main
  Home:   https://github.com/WebKit/WebKit
  Commit: fdc295002ed6c111bc2e2ea618e4c294b68daedf
      https://github.com/WebKit/WebKit/commit/fdc295002ed6c111bc2e2ea618e4c294b68daedf
  Author: Wenson Hsieh <wenson_hsieh at apple.com>
  Date:   2022-10-20 (Thu, 20 Oct 2022)

  Changed paths:
    M Source/WebKit/UIProcess/ios/WKContentViewInteraction.mm
    M Tools/TestWebKitAPI/TestWebKitAPI.xcodeproj/project.pbxproj
    A Tools/TestWebKitAPI/Tests/ios/CustomContentViewGestures.mm

  Log Message:
  -----------
  MobileMail sometimes crashes underneath -[WKContentView(WKInteraction) deferringGestures]
https://bugs.webkit.org/show_bug.cgi?id=246823
rdar://100971798

Reviewed by Megan Gardner.

>From crash telemetry, it's apparently possible for UIKit to call into WKContentView's gesture
recognizer delegate methods before `-setUpInteraction` has been invoked. If this happens, we end up
crashing due to an ObjC exception, when attempting to insert nil deferring gestures into an array
under the call to `-deferringGestures`. While I wasn't able to reproduce this crash in Mail, I was
able to reproduce it by creating a simple test app that:

1. Creates a new `WKWebView`
2. Immediately calls `_close` on the web view (thereby preventing a web process from being launched
   right away upon being parented)
3. Parent the web view in a visible window
4. Create new `UIGestureRecognizer`s and add them to the content view
5. Call into `-gestureRecognizer:shouldRecognizeSimultaneouslyWithGestureRecognizer:` with the
   custom gestures.

To fix this, we simply make `-deferringGestures` robust in this case by adding null checks.

Test: CustomContentViewGestures.DoNotCrashWhenCheckingGestureDelegateInNewWebView

* Source/WebKit/UIProcess/ios/WKContentViewInteraction.mm:
(-[WKContentView deferringGestures]):
* Tools/TestWebKitAPI/TestWebKitAPI.xcodeproj/project.pbxproj:
* Tools/TestWebKitAPI/Tests/ios/CustomContentViewGestures.mm: Added.

Canonical link: https://commits.webkit.org/255804@main