Bug 303833 – Web Inspector: Sources Navigation Sidebar is sometimes empty on page reload

• Status: RESOLVED
• Resolution: FIXED
• Component: Web Inspector

[Razvan Caliman]

This intermittent issue is caused by an unhandled exception.
In a Release build, this manifests as a an empty tree outline for the main frame.

Steps:
- inspect webkit.org
- go to Sources tab
- select a resource from the sidebar
- reload the page
- select another resource from the sidebar
- reload the page again

Result:
Sometimes, the tree outline for the main frame is empty. Its disclosure triangle shows it expanded, but there are no children.
Toggling the disclosure triangle off and back on again reveals the tree elements for loaded resources.

---

TypeError:​ undefined is not an object (evaluating 'treeElement.parent._childrenListNode.appendChild')​ (at TreeOutline.js:​1001:​49)​
    _updateVirtualizedElements @ TreeOutline.js:​1001:​49
    boundUpdateVirtualizedElements @ TreeOutline.js:​688:​44
    _execute @ Debouncer.js:​132:​29
    force @ Debouncer.js:​63:​22
    reveal @ TreeElement.js:​508:​70
    revealAndSelect @ TreeElement.js:​564:​20
    _revealAndSelectRepresentedObject @ ContentBrowserTabContentView.js:​317:​40
    _contentBrowserCurrentContentViewDidChange @ ContentBrowserTabContentView.js:​299:​47
    dispatch @ Object.js:​134:​35
    dispatchEventToListeners @ Object.js:​142:​17
    _currentContentViewDidChange @ ContentBrowser.js:​540:​38
    dispatch @ Object.js:​134:​35
    dispatchEventToListeners @ Object.js:​142:​17
    showBackForwardEntryForIndex @ ContentViewContainer.js:​173:​38
    showContentView @ ContentViewContainer.js:​148:​42
    showDefaultContentViewForTreeElement @ NavigationSidebarPanel.js:​208:​82
    _checkElementsForPendingViewStateCookie @ NavigationSidebarPanel.js:​708:​79
    _treeElementAddedOrChanged @ NavigationSidebarPanel.js:​613:​57
    dispatch @ Object.js:​134:​35
    dispatchEventToListeners @ Object.js:​142:​17
    insertChild @ TreeOutline.js:​290:​54
    _insertChildTreeElement @ FolderizedTreeElement.js:​246:​38
    _addTreeElement @ FolderizedTreeElement.js:​216:​37
    addChildForRepresentedObject @ FolderizedTreeElement.js:​103:​29
    onpopulate @ FrameTreeElement.js:​169:​46
    traverseNextTreeElement @ TreeElement.js:​616:​31
    ?​ @ NavigationSidebarPanel.js:​660:​80
    forEach @ [native code]​
    _checkOutlinesForPendingViewStateCookie @ NavigationSidebarPanel.js:​653:​41
    restoreStateFromCookie @ NavigationSidebarPanel.js:​251:​53
    restoreStateFromCookie @ TabContentView.js:​165:​63
    ?​ @ Main.js:​1756:​46
    ?​ @ Main.js:​1732:​37

[Radar WebKit Bug Importer]

<rdar://problem/166141968>

[Razvan Caliman]

Created attachment 477675 [details]
Screen recording of issue

[Razvan Caliman]

Pull request: https://github.com/WebKit/WebKit/pull/55109

[EWS]

Committed 304221@main (97a29a8fcc7f): <https://commits.webkit.org/304221@main>

Reviewed commits have been landed. Closing PR #55109 and removing active labels.