Bug 1907289 - Reflow table cell if collapsed borders have changed. r=dshin, a=dmeehan

A potentially better approach could be to call FrameNeedsReflow from
nsBCTableCellFrame::SetBorderWidth... But it seems that might
over-invalidate quite a lot when recalculating borders, since it seems
we reset the relevant ones and then accumulate directly on the frame.

If that seems like a better approach, happy to give that a try. This
should be less risky for performance changes in general tho.

Differential Revision: https://phabricator.services.mozilla.com/D216409

layout/tables/nsTableCellFrame.cpp

@@ -889,6 +889,14 @@ void nsTableCellFrame::Reflow(nsPresContext* aPresContext,
   PushDirtyBitToAbsoluteFrames();
 }
 
+void nsBCTableCellFrame::Reflow(nsPresContext* aPresContext,
+                                ReflowOutput& aDesiredSize,
+                                const ReflowInput& aReflowInput,
+                                nsReflowStatus& aStatus) {
+  nsTableCellFrame::Reflow(aPresContext, aDesiredSize, aReflowInput, aStatus);
+  mLastUsedBorder = GetUsedBorder();
+}
+
 /* ----- global methods ----- */
 
 NS_QUERYFRAME_HEAD(nsTableCellFrame)
@@ -944,9 +952,7 @@ nsresult nsTableCellFrame::GetFrameName(nsAString& aResult) const {
 
 nsBCTableCellFrame::nsBCTableCellFrame(ComputedStyle* aStyle,
                                        nsTableFrame* aTableFrame)
-    : nsTableCellFrame(aStyle, aTableFrame, kClassID) {
-  mBStartBorder = mIEndBorder = mBEndBorder = mIStartBorder = 0;
-}
+    : nsTableCellFrame(aStyle, aTableFrame, kClassID) {}
 
 nsBCTableCellFrame::~nsBCTableCellFrame() = default;
 

layout/tables/nsTableCellFrame.h

@@ -216,6 +216,7 @@ class nsTableCellFrame : public nsContainerFrame,
   }
 
   virtual mozilla::LogicalMargin GetBorderWidth(mozilla::WritingMode aWM) const;
+  virtual bool BCBordersChanged() const { return false; }
 
   void DecorateForSelection(DrawTarget* aDrawTarget, nsPoint aPt);
 
@@ -265,10 +266,15 @@ class nsBCTableCellFrame final : public nsTableCellFrame {
   NS_DECL_FRAMEARENA_HELPERS(nsBCTableCellFrame)
 
   nsBCTableCellFrame(ComputedStyle* aStyle, nsTableFrame* aTableFrame);
+  void Reflow(nsPresContext*, ReflowOutput&, const ReflowInput&,
+              nsReflowStatus&) override;
 
   ~nsBCTableCellFrame();
 
   nsMargin GetUsedBorder() const override;
+  bool BCBordersChanged() const override {
+    return GetUsedBorder() != mLastUsedBorder;
+  }
 
   // Get the *inner half of the border only*, in twips.
   mozilla::LogicalMargin GetBorderWidth(
@@ -289,10 +295,12 @@ class nsBCTableCellFrame final : public nsTableCellFrame {
  private:
   // These are the entire width of the border (the cell edge contains only
   // the inner half).
-  nscoord mBStartBorder;
-  nscoord mIEndBorder;
-  nscoord mBEndBorder;
-  nscoord mIStartBorder;
+  nscoord mBStartBorder = 0;
+  nscoord mIEndBorder = 0;
+  nscoord mBEndBorder = 0;
+  nscoord mIStartBorder = 0;
+
+  nsMargin mLastUsedBorder;
 };
 
 // Implemented here because that's a sane-ish way to make the includes work out.

layout/tables/nsTableRowFrame.cpp

@@ -755,14 +755,14 @@ void nsTableRowFrame::ReflowChildren(nsPresContext* aPresContext,
       NS_ASSERTION(kidFrame->GetWritingMode() == wm,
                    "expected consistent writing-mode within table");
       LogicalSize cellDesiredSize = kidFrame->GetDesiredSize();
-      if ((availCellISize != kidFrame->GetPriorAvailISize()) ||
-          (cellDesiredSize.ISize(wm) > kidFrame->GetPriorAvailISize()) ||
+      if (availCellISize != kidFrame->GetPriorAvailISize() ||
+          cellDesiredSize.ISize(wm) > kidFrame->GetPriorAvailISize() ||
           HasAnyStateBits(NS_FRAME_IS_DIRTY) || isPaginated ||
           kidFrame->IsSubtreeDirty() ||
           // See if it needs a special reflow, or if it had one that we need to
           // undo.
           kidFrame->HasAnyStateBits(NS_FRAME_CONTAINS_RELATIVE_BSIZE) ||
-          HasPctBSize()) {
+          kidFrame->BCBordersChanged() || HasPctBSize()) {
         // Reflow the cell to fit the available isize, bsize
         // XXX The old IR_ChildIsDirty code used availCellISize here.
         LogicalSize kidAvailSize(wm, availCellISize,

testing/web-platform/tests/css/css-tables/collapsed-border-remove-row-group-ref.html

@@ -0,0 +1,24 @@
+<!doctype html>
+<meta charset="utf-8">
+<title>CSS test reference</title>
+<style>
+  table {
+    border-collapse: collapse;
+  }
+
+  td {
+    border-bottom: 10px solid;
+  }
+</style>
+<table>
+  <thead>
+    <tr>
+      <td>Something</td>
+    </tr>
+  </thead>
+  <tbody>
+    <tr>
+      <td>Body</td>
+    </tr>
+  </tbody>
+</table>

testing/web-platform/tests/css/css-tables/collapsed-border-remove-row-group.html

@@ -0,0 +1,39 @@
+<!doctype html>
+<meta charset="utf-8">
+<title>collapsed border recalculation as a result of removal</title>
+<link rel="author" href="mailto:emilio@crisal.io" title="Emilio Cobos Álvarez">
+<link rel="author" href="https://mozilla.org" title="Mozilla">
+<link rel="help" href="https://drafts.csswg.org/css-tables/#border-collapse-property">
+<link rel="help" href="https://bugzilla.mozilla.org/show_bug.cgi?id=1907289">
+<link rel="match" href="collapsed-border-remove-row-group-ref.html">
+<style>
+  table {
+    border-collapse: collapse;
+  }
+  td {
+    border-bottom: 10px solid;
+  }
+</style>
+<table>
+  <thead>
+    <tr>
+      <td>Something</td>
+    </tr>
+  </thead>
+  <thead id="removeMe">
+    <tr>
+      <td style="border: 0">Something</td>
+    </tr>
+  </thead>
+  <tbody>
+    <tr>
+      <td>Body</td>
+    </tr>
+  </tbody>
+</table>
+<script>
+  onload = function () {
+    removeMe.getBoundingClientRect();
+    removeMe.remove();
+  };
+</script>