Inset box-shadow incorrectly positioned on table cells with collapsed borders

Ahmad-S792 · darinadler · commit aade63473a3e · 2026-02-16T12:37:19.000-08:00
https://bugs.webkit.org/show_bug.cgi?id=306607 rdar://169254286 Reviewed by Darin Adler. This patch aligns WebKit with Gecko / Firefox and Blink / Chromium. When painting inset box-shadows on table cells with collapsed borders, we were positioning the shadow too far inward, exposing the background color. This occurred because collapsed borders report half-widths through borderTop()/borderLeft() etc., but BackgroundPainter expects the border box to be at the outer edge when calculating inset shadow bounds. The fix expands the paint rect by the half-widths before passing it to BackgroundPainter for inset shadows. BackgroundPainter then subtracts these half-widths to compute the inner edge, correctly positioning the inset shadow at the true inner edge of the collapsed border. * Source/WebCore/rendering/RenderTableCell.cpp: (WebCore::RenderTableCell::paintBoxDecorations): * LayoutTests/TestExpectations: Progression Canonical link: https://commits.webkit.org/307661@main
diff --git a/LayoutTests/TestExpectations b/LayoutTests/TestExpectations
@@ -6857,7 +6857,6 @@ imported/w3c/web-platform-tests/css/css-tables/absolute-tables-007.html [ ImageO
 imported/w3c/web-platform-tests/css/css-tables/absolute-tables-011.tentative.html [ ImageOnlyFailure ]
 imported/w3c/web-platform-tests/css/css-tables/absolute-tables-015.html [ ImageOnlyFailure ]
 imported/w3c/web-platform-tests/css/css-tables/anonymous-table-ws-001.html [ ImageOnlyFailure ]
-imported/w3c/web-platform-tests/css/css-tables/box-shadow-001.html [ ImageOnlyFailure ]
 imported/w3c/web-platform-tests/css/css-tables/col-definite-min-size-001.html [ ImageOnlyFailure ]
 imported/w3c/web-platform-tests/css/css-tables/fixup-dynamic-anonymous-inline-table-001.html [ ImageOnlyFailure ]
 imported/w3c/web-platform-tests/css/css-tables/fixup-dynamic-anonymous-inline-table-002.html [ ImageOnlyFailure ]
diff --git a/Source/WebCore/rendering/RenderTableCell.cpp b/Source/WebCore/rendering/RenderTableCell.cpp
@@ -1643,7 +1643,12 @@ void RenderTableCell::paintBoxDecorations(PaintInfo& paintInfo, const LayoutPoin
     // Paint our cell background.
     paintBackgroundsBehindCell(paintInfo, paintOffset, this, paintOffset);
 
-    backgroundPainter.paintBoxShadow(paintRect, style(), Style::ShadowStyle::Inset);
+    // For collapsed borders, we expand from inner edge to outer edge for inset shadow painting.
+    LayoutRect insetShadowRect = paintRect;
+    if (table->collapseBorders())
+        insetShadowRect.expand(RectEdges<LayoutUnit> { borderTop(), borderRight(), borderBottom(), borderLeft() });
+
+    backgroundPainter.paintBoxShadow(insetShadowRect, style(), Style::ShadowStyle::Inset);
 
     if (!style().border().hasBorder() || table->collapseBorders())
         return;
