Bug 323851

On a Google search result page for a film, the "Where to watch" card expands into a panel of provider rows. Each row is a plain `<a href>`. In Safari, pressing one closes the panel and nothing navigates. Chrome and Firefox navigate on the first press. **Steps to reproduce** 1. Search Google for a film with several streaming providers. "soylent green" works. 2. Click the "Where to watch" header, or the "+N more" chip, to expand the panel. 3. Click any provider row. Result: the panel collapses and the page stays where it is. Expected: the browser navigates to the provider, as it does in Chrome and Firefox. **Root cause** WebKit does not give focus to a plain link when it is pressed. `HTMLAnchorElement::isMouseFocusable()` returns `HTMLElement::supportsFocus()` for a link, which is false unless the link carries `tabindex` or `contenteditable`. Google's panel closes itself when focus leaves it. Its container carries `jsaction="...;blur:.CLIENT"`, and that handler branches on `relatedTarget`. Measured on the live page: mousedown on a provider link activeElement before: the panel header activeElement after: body +1 ms blur and focusout on the header, relatedTarget null +3 ms the reveal class is removed and the panel collapses +263 ms mouseup lands on a different element, the panel having shrunk the click is therefore retargeted to a common ancestor The link never receives a click, so nothing navigates. The visible symptom is the panel closing, but the closing is the cause rather than a second effect. The contrasting case in the same session shows the handler is doing what it was written to do. The "+N more" chip is `role="button" tabindex="0"`, so it takes focus, `relatedTarget` stays inside the panel, and the panel stays open. Only the bare links fall out. Confirmed by adding `tabindex="0"` to the six provider links in the page: they become mouse focusable and the very next press navigates. **Why a quirk rather than a behaviour change** WebKit is not violating the specification. HTML leaves this to the user agent: > A focusable area is said to be click focusable if the user agent determines that it is click focusable. https://html.spec.whatwg.org/multipage/interaction.html#focus The specification only says user agents should treat focusable areas with a non-null tabindex as click focusable, which WebKit already does. So this is a divergence from the other engines, not a defect, and changing WebKit's default focus-on-press behaviour is a much larger change than this site needs. **Proposed fix** A new quirk, `needsExpandablePanelAnchorToBeMouseFocusableQuirk`, narrower than the existing `needsAnchorToBeMouseFocusableQuirk` that covers dictionary.com and thesaurus.com for the same root cause: URL scope anyTopLevelDomain("google") and pathIs("/search") element scope only anchors with an ancestor carrying data-expc So only links inside the expandable panel become mouse focusable. Every other link on a Google results page is unaffected, and no other Google property is touched. `anyTopLevelDomain` is needed because the panel is locale-dependent and the reproduction is easiest on a ccTLD. The element check is affordable because `isMouseFocusable()` runs on mouse press, not during style resolution or painting. The ancestor walk is bounded at 12 levels. Known weakness, stated up front: `data-expc` is Google's markup. If they rename it the quirk stops matching and the bug returns silently. The alternative is a domain-wide quirk, which changes focus behaviour for every link on the domain. This patch takes the narrower scope; widening it later is a one-line change. **Test coverage** `fast/quirks/active-quirks-by-domain.html` gains three URLs covering the scoping: the results page, a deeper path under /search that must not match, and a ccTLD results page. Six expected files updated, since the quirk is cocoa-only and glib must show no change. **Console output** No new logging is needed. `Quirks::logQuirksToConsoleIfNecessary()`, called from `FrameLoader.cpp` on main-frame load, already lists every quirk enabled for the URL. On a Google search page the Web Inspector console will show a warning of the form: <url> has active WebKit quirks: MaybeBypassBackForwardCache, NeedsExpandablePanelAnchorToBeMouseFocusableQuirk. Visit https://docs.webkit.org/Infrastructure/Quirks.html for more information. Note this reports quirks enabled for the URL, not quirks that changed behaviour on a given interaction, which is how every table-driven quirk reports. **Reproducing the bug after the quirk lands** The quirk hides the bug, so to see the original behaviour again, turn site-specific quirks off: MiniBrowser Settings menu, uncheck "Enable site-specific quirks" Safari Develop menu, the compatibility setting that disables site-specific hacks With quirks disabled, steps 1 to 3 above fail exactly as reported. With quirks enabled, the provider link navigates. That difference is the check that this patch is doing what it claims. For a layout test the equivalent switch is `internals.setTopDocumentURLForQuirks(url)`, which turns `needsSiteSpecificQuirks` on and sets the URL used for matching, plus `internals.activeQuirks()` to read back what is enabled.