297033 2025-08-06 20:04:18 -0700 [css-anchor-position-1] Changing window focus causes relayout on anchor() tests 2025-08-06 20:10:18 -0700 1 1 1 Unclassified WebKit Layout and Rendering WebKit Local Build Unspecified Unspecified NEW InRadar P2 Normal --- 291856 1 fantasai.bugs koivisto bfulgham kiet.ho simon.fraser webkit-bug-importer zalan oldest_to_newest 2134832 0 fantasai.bugs 2025-08-06 20:04:18 -0700 For some reason, we are triggering relayout when the window changes focus on anchor positioning tests such as https://wpt.live/css/css-anchor-position/anchor-scope-scroll.html This is noticeable if you turn on logging. Seems like an excessive amount of work given nothing is supposed to change? 2134833 1 webkit-bug-importer 2025-08-06 20:04:26 -0700 <rdar://problem/157715763> 2134835 2 zalan 2025-08-06 20:10:18 -0700 It looks like the anchored element's inset value goes from fixed to auto on window focus (which then triggers layout). in RenderStyle::changeRequiresLayout (lldb) expr a.m_sides[0] (const std::array<WebCore::Style::InsetEdge, 4>::value_type) $5 = { WebCore::Style::LengthWrapperBase<WebCore::Style::LengthPercentage<WebCore::CSS::Range, float>, WebCore::Constant<WebCore::CSSValueAuto> > = { m_value = { = (m_intValue = 1126105088, m_floatValue = 159, m_calculationValueHandle = 1126105088) m_type = Fixed m_hasQuirk = false m_isFloat = true m_isEmptyValue = false } } } (lldb) expr b.m_sides[0] (const std::array<WebCore::Style::InsetEdge, 4>::value_type) $6 = { WebCore::Style::LengthWrapperBase<WebCore::Style::LengthPercentage<WebCore::CSS::Range, float>, WebCore::Constant<WebCore::CSSValueAuto> > = { m_value = { = (m_intValue = 0, m_floatValue = 0, m_calculationValueHandle = 0) m_type = Auto m_hasQuirk = false m_isFloat = true m_isEmptyValue = false } } }