From: L. David Baron <dbaron@dbaron.org>

Bug 1307853 - Set inline-resize flag when the content-box size is changing (in addition to border-box).

MozReview-Commit-ID: FjUwuQB8g5j

diff --git a/layout/generic/ReflowInput.cpp b/layout/generic/ReflowInput.cpp
--- a/layout/generic/ReflowInput.cpp
+++ b/layout/generic/ReflowInput.cpp
@@ -517,19 +517,35 @@ IsQuirkContainingBlockHeight(const Reflo
   return true;
 }
 
 
 void
 ReflowInput::InitResizeFlags(nsPresContext* aPresContext, nsIAtom* aFrameType)
 {
   const WritingMode wm = mWritingMode; // just a shorthand
+  // We should report that we have a resize in the inline dimension if
+  // *either* the border-box size or the content-box size in that
+  // dimension has changed.  It might not actually be necessary to do
+  // this if the border-box size has changed and the content-box size
+  // has not changed, but since we've historically used the flag to mean
+  // border-box size change, continue to do that.  (It's possible for
+  // the content-box size to change without a border-box size change or
+  // a style change given a fixed width, box-sizing:border-box, and
+  // percentage padding.
+  // FIXME: Note that this might produce some incorrect results (both
+  // false positives and false negatives) in the presence of style
+  // changes since the current concept of content-box width might
+  // reflect style changes if the UsedPaddingProperty() was not used.
+  // This is not currently a real problem since border and padding
+  // changes currently produce nsChangeHint_NeedDirtyReflow hints.
   bool isIResize =
     mFrame->ISize(wm) !=
-      ComputedISize() + ComputedLogicalBorderPadding().IStartEnd(wm);
+      ComputedISize() + ComputedLogicalBorderPadding().IStartEnd(wm) ||
+    mFrame->ContentISize(wm) != ComputedISize();
 
   if ((mFrame->GetStateBits() & NS_FRAME_FONT_INFLATION_FLOW_ROOT) &&
       nsLayoutUtils::FontSizeInflationEnabled(aPresContext)) {
     // Create our font inflation data if we don't have it already, and
     // give it our current width information.
     bool dirty = nsFontInflationData::UpdateFontInflationDataISizeFor(*this) &&
                  // Avoid running this at the box-to-block interface
                  // (where we shouldn't be inflating anyway, and where
diff --git a/layout/generic/nsIFrame.h b/layout/generic/nsIFrame.h
--- a/layout/generic/nsIFrame.h
+++ b/layout/generic/nsIFrame.h
@@ -799,16 +799,22 @@ public:
   nscoord BStart(mozilla::WritingMode aWritingMode,
                  const nsSize& aContainerSize) const {
     return GetLogicalPosition(aWritingMode, aContainerSize).B(aWritingMode);
   }
   nscoord ISize() const { return ISize(GetWritingMode()); }
   nscoord ISize(mozilla::WritingMode aWritingMode) const {
     return GetLogicalSize(aWritingMode).ISize(aWritingMode);
   }
+  nscoord ContentISize() const { return ContentISize(GetWritingMode()); }
+  nscoord ContentISize(mozilla::WritingMode aWritingMode) const {
+    auto bp = GetLogicalUsedBorderAndPadding(aWritingMode);
+    bp.ApplySkipSides(GetLogicalSkipSides());
+    return std::max(0, ISize(aWritingMode) - bp.IStartEnd(aWritingMode));
+  }
   nscoord BSize() const { return BSize(GetWritingMode()); }
   nscoord BSize(mozilla::WritingMode aWritingMode) const {
     return GetLogicalSize(aWritingMode).BSize(aWritingMode);
   }
   nscoord ContentBSize() const { return ContentBSize(GetWritingMode()); }
   nscoord ContentBSize(mozilla::WritingMode aWritingMode) const {
     auto bp = GetLogicalUsedBorderAndPadding(aWritingMode);
     bp.ApplySkipSides(GetLogicalSkipSides());
diff --git a/layout/style/nsStyleStruct.cpp b/layout/style/nsStyleStruct.cpp
--- a/layout/style/nsStyleStruct.cpp
+++ b/layout/style/nsStyleStruct.cpp
@@ -431,16 +431,19 @@ nsStylePadding::CalcDifference(const nsS
 {
   if (mPadding == aNewData.mPadding) {
     return nsChangeHint(0);
   }
   // Padding differences can't affect descendant intrinsic sizes, but do need
   // to force children to reflow so that we can reposition them, since their
   // offsets are from our frame bounds but our content rect's position within
   // those bounds is moving.
+  // XXXdbaron: Note that not returning nsChangeHint_NeedDirtyReflow for
+  // mPadding differences would first require fixing the issue at the
+  // start of ReflowInput::InitResizeFlags.
   return NS_STYLE_HINT_REFLOW & ~nsChangeHint_ClearDescendantIntrinsics;
 }
 
 nsStyleBorder::nsStyleBorder(StyleStructContext aContext)
   : mBorderColors(nullptr)
   , mBorderImageFill(NS_STYLE_BORDER_IMAGE_SLICE_NOFILL)
   , mBorderImageRepeatH(NS_STYLE_BORDER_IMAGE_REPEAT_STRETCH)
   , mBorderImageRepeatV(NS_STYLE_BORDER_IMAGE_REPEAT_STRETCH)
@@ -567,16 +570,19 @@ nsStyleBorder::Destroy(nsPresContext* aC
     FreeByObjectID(eArenaObjectID_nsStyleBorder, this);
 }
 
 nsChangeHint
 nsStyleBorder::CalcDifference(const nsStyleBorder& aNewData) const
 {
   // XXXbz we should be able to return a more specific change hint for
   // at least GetComputedBorder() differences...
+  // XXXdbaron: Note that not returning nsChangeHint_NeedDirtyReflow for
+  // GetComputedBorder() differences would first require fixing the
+  // issue at the start of ReflowInput::InitResizeFlags.
   if (mTwipsPerPixel != aNewData.mTwipsPerPixel ||
       GetComputedBorder() != aNewData.GetComputedBorder() ||
       mFloatEdge != aNewData.mFloatEdge ||
       mBorderImageOutset != aNewData.mBorderImageOutset ||
       mBoxDecorationBreak != aNewData.mBoxDecorationBreak) {
     return NS_STYLE_HINT_REFLOW;
   }