Issue mcp-graveyard/UXP#1230 - Part 1: Fix Back-computing percentages for intrinsic sizing in Layout CSS-Grid

List of relevant patches applied:

1398537 part 2 - [css-multicol] Implement percentages for 'column-gap' (Gecko part).

1434478 part 1 - [css-grid] Stop back-computing percentage grid gaps when the percentage basis is indefinite. Treat them as zero sized instead.

1434478 part 2 - Stop back-computing percentage padding/margin when the percentage basis is indefinite. Treat them as zero sized instead.

1434478 part 3 - Remove IntrinsicISizeOffsetData::hPctPadding/hPctMargin members since they are now unused.

1434478 part 4 - Factor out constants like NS_UNCONSTRAINEDSIZE so they can be used in headers without needing nsIFrame.h (idempotent patch).

1434478 part 5 - Create nsLayoutUtils::ResolveToLength for resolving CSS <length-percentage> (idempotent patch).

1434478 part 6 - Propagate a percentage basis to nsIFrame::IntrinsicISizeOffsets for resolving padding/margin.

This is needed only for CSS Grid since in other cases we're only using IntrinsicISizeOffsets in the inline-axis and the percentage basis is always indefinite for *intrinsic sizing*. When calculating the intrinsic size of grid items in the grid container's block axis however, we do have a definite size for the grid area in the inline-axis and it should be used per: https://drafts.csswg.org/css-grid/#algo-overview "2. Next, the track sizing algorithm resolves the sizes of the grid rows, using the grid column sizes calculated in the previous step." (Percentage padding/margin for grid items is always resolved against the grid area's inline-size nowadays.)

16 files changed, 240 insertions, 319 deletions

diff --git a/layout/base/LayoutConstants.h b/layout/base/LayoutConstants.h
new file mode 100644
index 0000000000..cd6e1c3f55
--- /dev/null
+++ b/layout/base/LayoutConstants.h
@@ -0,0 +1,31 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+/* constants used throughout the Layout module */
+
+#ifndef LayoutConstants_h___
+#define LayoutConstants_h___
+
+#include "nsSize.h"  // for NS_MAXSIZE
+
+/**
+ * Constant used to indicate an unconstrained size.
+ */
+#define NS_UNCONSTRAINEDSIZE NS_MAXSIZE
+
+// NOTE: There are assumptions all over that these have the same value,
+//       namely NS_UNCONSTRAINEDSIZE.
+#define NS_INTRINSICSIZE    NS_UNCONSTRAINEDSIZE
+#define NS_AUTOHEIGHT       NS_UNCONSTRAINEDSIZE
+#define NS_AUTOOFFSET       NS_UNCONSTRAINEDSIZE
+
+// +1 is to avoid clamped huge margin values being processed as auto margins
+#define NS_AUTOMARGIN       (NS_UNCONSTRAINEDSIZE + 1)
+
+#define NS_INTRINSIC_WIDTH_UNKNOWN nscoord_MIN
+
+
+#endif // LayoutConstants_h___
diff --git a/layout/base/moz.build b/layout/base/moz.build
index 4308a6e4d0..afc683665a 100644
--- a/layout/base/moz.build
+++ b/layout/base/moz.build
@@ -13,6 +13,9 @@ with Files('Display*'):
 with Files('FrameLayerBuilder.*'):
     BUG_COMPONENT = ('Core', 'Layout: View Rendering')
 
+with Files('LayoutConstants.*'):
+    BUG_COMPONENT = ('Core', 'Layout: View Rendering')
+
 with Files('LayerState.*'):
     BUG_COMPONENT = ('Core', 'Layout: View Rendering')
 
@@ -63,6 +66,7 @@ EXPORTS += [
     'FrameLayerBuilder.h',
     'FrameProperties.h',
     'LayerState.h',
+    'LayoutConstants.h',
     'LayoutLogging.h',
     'nsArenaMemoryStats.h',
     'nsBidi.h',
diff --git a/layout/base/nsLayoutUtils.cpp b/layout/base/nsLayoutUtils.cpp
index 06690b208b..21d20c69fa 100644
--- a/layout/base/nsLayoutUtils.cpp
+++ b/layout/base/nsLayoutUtils.cpp
@@ -4671,8 +4671,6 @@ GetDefiniteSize(const nsStyleCoord&       aStyle,
         nscoord pb = aIsInlineAxis ? aPercentageBasis.value().ISize(wm)
                                    : aPercentageBasis.value().BSize(wm);
         if (pb == NS_UNCONSTRAINEDSIZE) {
-          // XXXmats given that we're calculating an intrinsic size here,
-          // maybe we should back-compute the calc-size using AddPercents?
           return false;
         }
         *aResult = std::max(0, calc->mLength +
@@ -4916,12 +4914,9 @@ AddIntrinsicSizeOffset(nsRenderingContext* aRenderingContext,
   nscoord result = aContentSize;
   nscoord min = aContentMinSize;
   nscoord coordOutsideSize = 0;
-  float pctOutsideSize = 0;
-  float pctTotal = 0.0f;
 
   if (!(aFlags & nsLayoutUtils::IGNORE_PADDING)) {
     coordOutsideSize += aOffsets.hPadding;
-    pctOutsideSize += aOffsets.hPctPadding;
   }
 
   coordOutsideSize += aOffsets.hBorder;
@@ -4929,21 +4924,15 @@ AddIntrinsicSizeOffset(nsRenderingContext* aRenderingContext,
   if (aBoxSizing == StyleBoxSizing::Border) {
     min += coordOutsideSize;
     result = NSCoordSaturatingAdd(result, coordOutsideSize);
-    pctTotal += pctOutsideSize;
 
     coordOutsideSize = 0;
-    pctOutsideSize = 0.0f;
   }
 
   coordOutsideSize += aOffsets.hMargin;
-  pctOutsideSize += aOffsets.hPctMargin;
 
   min += coordOutsideSize;
   result = NSCoordSaturatingAdd(result, coordOutsideSize);
-  pctTotal += pctOutsideSize;
 
-  const bool shouldAddPercent = aType == nsLayoutUtils::PREF_ISIZE ||
-                                (aFlags & nsLayoutUtils::ADD_PERCENTS);
   nscoord size;
   if (aType == nsLayoutUtils::MIN_ISIZE &&
       (((aStyleSize.HasPercent() || aStyleMaxSize.HasPercent()) &&
@@ -4961,18 +4950,6 @@ AddIntrinsicSizeOffset(nsRenderingContext* aRenderingContext,
              GetIntrinsicCoord(aStyleSize, aRenderingContext, aFrame,
                                PROP_WIDTH, size)) {
     result = size + coordOutsideSize;
-    if (shouldAddPercent) {
-      result = nsLayoutUtils::AddPercents(result, pctOutsideSize);
-    }
-  } else {
-    // NOTE: We could really do a lot better for percents and for some
-    // cases of calc() containing percent (certainly including any where
-    // the coefficient on the percent is positive and there are no max()
-    // expressions).  However, doing better for percents wouldn't be
-    // backwards compatible.
-    if (shouldAddPercent) {
-      result = nsLayoutUtils::AddPercents(result, pctTotal);
-    }
   }
 
   nscoord maxSize = aFixedMaxSize ? *aFixedMaxSize : 0;
@@ -4980,9 +4957,6 @@ AddIntrinsicSizeOffset(nsRenderingContext* aRenderingContext,
       GetIntrinsicCoord(aStyleMaxSize, aRenderingContext, aFrame,
                         PROP_MAX_WIDTH, maxSize)) {
     maxSize += coordOutsideSize;
-    if (shouldAddPercent) {
-      maxSize = nsLayoutUtils::AddPercents(maxSize, pctOutsideSize);
-    }
     if (result > maxSize) {
       result = maxSize;
     }
@@ -4993,17 +4967,11 @@ AddIntrinsicSizeOffset(nsRenderingContext* aRenderingContext,
       GetIntrinsicCoord(aStyleMinSize, aRenderingContext, aFrame,
                         PROP_MIN_WIDTH, minSize)) {
     minSize += coordOutsideSize;
-    if (shouldAddPercent) {
-      minSize = nsLayoutUtils::AddPercents(minSize, pctOutsideSize);
-    }
     if (result < minSize) {
       result = minSize;
     }
   }
 
-  if (shouldAddPercent) {
-    min = nsLayoutUtils::AddPercents(min, pctTotal);
-  }
   if (result < min) {
     result = min;
   }
@@ -5020,9 +4988,6 @@ AddIntrinsicSizeOffset(nsRenderingContext* aRenderingContext,
                                                      : devSize.width);
     // GetMinimumWidgetSize() returns a border-box width.
     themeSize += aOffsets.hMargin;
-    if (shouldAddPercent) {
-      themeSize = nsLayoutUtils::AddPercents(themeSize, aOffsets.hPctMargin);
-    }
     if (themeSize > result || !canOverride) {
       result = themeSize;
     }
@@ -5267,9 +5232,19 @@ nsLayoutUtils::IntrinsicForAxis(PhysicalAxis              aAxis,
     min = aFrame->GetMinISize(aRenderingContext);
   }
 
+  nscoord pmPercentageBasis = NS_UNCONSTRAINEDSIZE;
+  if (aPercentageBasis.isSome()) {
+    // The padding/margin percentage basis is the inline-size in the parent's
+    // writing-mode.
+    auto childWM = aFrame->GetWritingMode();
+    pmPercentageBasis =
+      aFrame->GetParent()->GetWritingMode().IsOrthogonalTo(childWM) ?
+        aPercentageBasis->BSize(childWM) :
+        aPercentageBasis->ISize(childWM);
+  }
   nsIFrame::IntrinsicISizeOffsetData offsets =
-    MOZ_LIKELY(isInlineAxis) ? aFrame->IntrinsicISizeOffsets()
-                             : aFrame->IntrinsicBSizeOffsets();
+    MOZ_LIKELY(isInlineAxis) ? aFrame->IntrinsicISizeOffsets(pmPercentageBasis)
+                             : aFrame->IntrinsicBSizeOffsets(pmPercentageBasis);
   nscoord contentBoxSize = result;
   result = AddIntrinsicSizeOffset(aRenderingContext, aFrame, offsets, aType,
                                   boxSizing, result, min, styleISize,
@@ -5310,11 +5285,12 @@ nsLayoutUtils::IntrinsicForContainer(nsRenderingContext* aRenderingContext,
 }
 
 /* static */ nscoord
-nsLayoutUtils::MinSizeContributionForAxis(PhysicalAxis        aAxis,
+nsLayoutUtils::MinSizeContributionForAxis(PhysicalAxis       aAxis,
                                           nsRenderingContext* aRC,
-                                          nsIFrame*           aFrame,
-                                          IntrinsicISizeType  aType,
-                                          uint32_t            aFlags)
+                                          nsIFrame*          aFrame,
+                                          IntrinsicISizeType aType,
+                                          const LogicalSize& aPercentageBasis,
+                                          uint32_t           aFlags)
 {
   MOZ_ASSERT(aFrame);
   MOZ_ASSERT(aFrame->IsFlexOrGridItem(),
@@ -5328,9 +5304,7 @@ nsLayoutUtils::MinSizeContributionForAxis(PhysicalAxis        aAxis,
                 aWM.IsVertical() ? "vertical" : "horizontal");
 #endif
 
-  // Note: this method is only meant for grid/flex items which always
-  // include percentages in their intrinsic size.
-  aFlags |= nsLayoutUtils::ADD_PERCENTS;
+  // Note: this method is only meant for grid/flex items.
   const nsStylePosition* const stylePos = aFrame->StylePosition();
   const nsStyleCoord* style = aAxis == eAxisHorizontal ? &stylePos->mMinWidth
                                                        : &stylePos->mMinHeight;
@@ -5375,11 +5349,17 @@ nsLayoutUtils::MinSizeContributionForAxis(PhysicalAxis        aAxis,
   // wrapping inside of it should not apply font size inflation.
   AutoMaybeDisableFontInflation an(aFrame);
 
-  PhysicalAxis ourInlineAxis =
-    aFrame->GetWritingMode().PhysicalAxis(eLogicalAxisInline);
+  // The padding/margin percentage basis is the inline-size in the parent's
+  // writing-mode.
+  auto childWM = aFrame->GetWritingMode();
+  nscoord pmPercentageBasis =
+    aFrame->GetParent()->GetWritingMode().IsOrthogonalTo(childWM) ?
+      aPercentageBasis.BSize(childWM) :
+      aPercentageBasis.ISize(childWM);
+  PhysicalAxis ourInlineAxis = childWM.PhysicalAxis(eLogicalAxisInline);
   nsIFrame::IntrinsicISizeOffsetData offsets =
-    ourInlineAxis == aAxis ? aFrame->IntrinsicISizeOffsets()
-                           : aFrame->IntrinsicBSizeOffsets();
+    ourInlineAxis == aAxis ? aFrame->IntrinsicISizeOffsets(pmPercentageBasis)
+                           : aFrame->IntrinsicBSizeOffsets(pmPercentageBasis);
   nscoord result = 0;
   nscoord min = 0;
 
diff --git a/layout/base/nsLayoutUtils.h b/layout/base/nsLayoutUtils.h
index 0a82dbf6a5..bba1f32652 100644
--- a/layout/base/nsLayoutUtils.h
+++ b/layout/base/nsLayoutUtils.h
@@ -6,6 +6,7 @@
 #ifndef nsLayoutUtils_h__
 #define nsLayoutUtils_h__
 
+#include "LayoutConstants.h"
 #include "mozilla/MemoryReporting.h"
 #include "mozilla/ArrayUtils.h"
 #include "mozilla/Maybe.h"
@@ -154,6 +155,7 @@ public:
   typedef mozilla::ScreenMargin ScreenMargin;
   typedef mozilla::LayoutDeviceIntSize LayoutDeviceIntSize;
   typedef mozilla::StyleGeometryBox StyleGeometryBox;
+  typedef mozilla::LogicalSize LogicalSize;
 
   /**
    * Finds previously assigned ViewID for the given content element, if any.
@@ -1381,7 +1383,8 @@ public:
    * variations if that's what matches aAxis) and its padding, border and margin
    * in the corresponding dimension.
    * @param aPercentageBasis an optional percentage basis (in aFrame's WM).
-   *   Pass NS_UNCONSTRAINEDSIZE if the basis is indefinite in either/both axes.
+   *   If the basis is indefinite in a given axis, pass a size with
+   *   NS_UNCONSTRAINEDSIZE in that component.
    *   If you pass Nothing() a percentage basis will be calculated from aFrame's
    *   ancestors' computed size in the relevant axis, if needed.
    * @param aMarginBoxMinSizeClamp make the result fit within this margin-box
@@ -1395,14 +1398,13 @@ public:
     IGNORE_PADDING = 0x01,
     BAIL_IF_REFLOW_NEEDED = 0x02, // returns NS_INTRINSIC_WIDTH_UNKNOWN if so
     MIN_INTRINSIC_ISIZE = 0x04, // use min-width/height instead of width/height
-    ADD_PERCENTS = 0x08, // apply AddPercents also for MIN_ISIZE
   };
   static nscoord
   IntrinsicForAxis(mozilla::PhysicalAxis aAxis,
                    nsRenderingContext*   aRenderingContext,
                    nsIFrame*             aFrame,
                    IntrinsicISizeType    aType,
-                   const mozilla::Maybe<mozilla::LogicalSize>& aPercentageBasis = mozilla::Nothing(),
+                   const mozilla::Maybe<LogicalSize>& aPercentageBasis = mozilla::Nothing(),
                    uint32_t              aFlags = 0,
                    nscoord               aMarginBoxMinSizeClamp = NS_MAXSIZE);
   /**
@@ -1427,31 +1429,18 @@ public:
    * calculates the result as if the 'min-' computed value is zero.
    * Otherwise, return NS_UNCONSTRAINEDSIZE.
    *
+   * @param aPercentageBasis the percentage basis (in aFrame's WM).
+   *   Pass NS_UNCONSTRAINEDSIZE if the basis is indefinite in either/both axes.
    * @note this behavior is specific to Grid/Flexbox (currently) so aFrame
    * should be a grid/flex item.
    */
-  static nscoord MinSizeContributionForAxis(mozilla::PhysicalAxis aAxis,
-                                            nsRenderingContext*   aRC,
-                                            nsIFrame*             aFrame,
-                                            IntrinsicISizeType    aType,
-                                            uint32_t              aFlags = 0);
-
-  /**
-   * This function increases an initial intrinsic size, 'aCurrent', according
-   * to the given 'aPercent', such that the size-increase makes up exactly
-   * 'aPercent' percent of the returned value.  If 'aPercent' or 'aCurrent' are
-   * less than or equal to zero the original 'aCurrent' value is returned.
-   * If 'aPercent' is greater than or equal to 1.0 the value nscoord_MAX is
-   * returned.
-   */
-  static nscoord AddPercents(nscoord aCurrent, float aPercent)
-  {
-    if (aPercent > 0.0f && aCurrent > 0) {
-      return MOZ_UNLIKELY(aPercent >= 1.0f) ? nscoord_MAX
-        : NSToCoordRound(float(aCurrent) / (1.0f - aPercent));
-    }
-    return aCurrent;
-  }
+  static nscoord
+  MinSizeContributionForAxis(mozilla::PhysicalAxis aAxis,
+                            nsRenderingContext*   aRC,
+                            nsIFrame*              aFrame,
+                            IntrinsicISizeType     aType,
+                            const LogicalSize&     aPercentageBasis,
+                            uint32_t               aFlags = 0);
 
   /*
    * Convert nsStyleCoord to nscoord when percentages depend on the
@@ -2876,6 +2865,62 @@ public:
   static nsRect ComputeGeometryBox(nsIFrame* aFrame,
                                    StyleGeometryBox aGeometryBox);
 
+  /**
+   * Resolve a CSS <length-percentage> value to a definite size.
+   */
+  template<bool clampNegativeResultToZero>
+  static nscoord ResolveToLength(const nsStyleCoord& aCoord,
+                                 nscoord aPercentageBasis)
+  {
+    NS_WARNING_ASSERTION(aPercentageBasis >= nscoord(0), "nscoord overflow?");
+
+    switch (aCoord.GetUnit()) {
+      case eStyleUnit_Coord:
+        MOZ_ASSERT(!clampNegativeResultToZero || aCoord.GetCoordValue() >= 0,
+                   "This value should have been rejected by the style system");
+        return aCoord.GetCoordValue();
+      case eStyleUnit_Percent:
+        if (aPercentageBasis == NS_UNCONSTRAINEDSIZE) {
+          return nscoord(0);
+        }
+        MOZ_ASSERT(!clampNegativeResultToZero || aCoord.GetPercentValue() >= 0,
+                   "This value should have been rejected by the style system");
+        return NSToCoordFloorClamped(aPercentageBasis *
+                                     aCoord.GetPercentValue());
+      case eStyleUnit_Calc: {
+        nsStyleCoord::Calc* calc = aCoord.GetCalcValue();
+        nscoord result;
+        if (aPercentageBasis == NS_UNCONSTRAINEDSIZE) {
+          result = calc->mLength;
+        } else {
+          result = calc->mLength +
+            NSToCoordFloorClamped(aPercentageBasis * calc->mPercent);
+        }
+        if (clampNegativeResultToZero && result < 0) {
+          return nscoord(0);
+        }
+        return result;
+      }
+      default:
+        MOZ_ASSERT_UNREACHABLE("Unexpected unit!");
+        return nscoord(0);
+    }
+  }
+
+  /**
+   * Resolve a column-gap/row-gap to a definite size.
+   * @note This method resolves 'normal' to zero.
+   *   Callers who want different behavior should handle 'normal' on their own.
+   */
+  static nscoord ResolveGapToLength(const nsStyleCoord& aGap,
+                                    nscoord aPercentageBasis)
+  {
+    if (aGap.GetUnit() == eStyleUnit_Normal) {
+      return nscoord(0);
+    }
+    return ResolveToLength<true>(aGap, aPercentageBasis);
+  }
+
 private:
   static uint32_t sFontSizeInflationEmPerLine;
   static uint32_t sFontSizeInflationMinTwips;
diff --git a/layout/generic/nsColumnSetFrame.cpp b/layout/generic/nsColumnSetFrame.cpp
index ad36ba1a88..6ea15d4d2f 100644
--- a/layout/generic/nsColumnSetFrame.cpp
+++ b/layout/generic/nsColumnSetFrame.cpp
@@ -183,18 +183,15 @@ nsColumnSetFrame::GetAvailableContentBSize(const ReflowInput& aReflowInput)
 
 static nscoord
 GetColumnGap(nsColumnSetFrame*    aFrame,
-             const nsStyleColumn* aColStyle)
+             const nsStyleColumn* aColStyle,
+             nscoord              aPercentageBasis)
 {
-  if (eStyleUnit_Normal == aColStyle->mColumnGap.GetUnit())
+  const auto& columnGap = aColStyle->mColumnGap;
+  if (columnGap.GetUnit() == eStyleUnit_Normal) {
     return aFrame->StyleFont()->mFont.size;
-  if (eStyleUnit_Coord == aColStyle->mColumnGap.GetUnit()) {
-    nscoord colGap = aColStyle->mColumnGap.GetCoordValue();
-    NS_ASSERTION(colGap >= 0, "negative column gap");
-    return colGap;
   }
 
-  NS_NOTREACHED("Unknown gap type");
-  return 0;
+  return nsLayoutUtils::ResolveGapToLength(columnGap, aPercentageBasis);
 }
 
 nsColumnSetFrame::ReflowConfig
@@ -227,7 +224,7 @@ nsColumnSetFrame::ChooseColumnStrategy(const ReflowInput& aReflowInput,
     colBSize = std::min(colBSize, aReflowInput.ComputedMaxBSize());
   }
 
-  nscoord colGap = GetColumnGap(this, colStyle);
+  nscoord colGap = GetColumnGap(this, colStyle, aReflowInput.ComputedISize());
   int32_t numColumns = colStyle->mColumnCount;
 
   // If column-fill is set to 'balance', then we want to balance the columns.
@@ -403,7 +400,7 @@ nsColumnSetFrame::GetMinISize(nsRenderingContext *aRenderingContext)
     // include n-1 column gaps.
     colISize = iSize;
     iSize *= colStyle->mColumnCount;
-    nscoord colGap = GetColumnGap(this, colStyle);
+    nscoord colGap = GetColumnGap(this, colStyle, NS_UNCONSTRAINEDSIZE);
     iSize += colGap * (colStyle->mColumnCount - 1);
     // The multiplication above can make 'width' negative (integer overflow),
     // so use std::max to protect against that.
@@ -424,7 +421,7 @@ nsColumnSetFrame::GetPrefISize(nsRenderingContext *aRenderingContext)
   nscoord result = 0;
   DISPLAY_PREF_WIDTH(this, result);
   const nsStyleColumn* colStyle = StyleColumn();
-  nscoord colGap = GetColumnGap(this, colStyle);
+  nscoord colGap = GetColumnGap(this, colStyle, NS_UNCONSTRAINEDSIZE);
 
   nscoord colISize;
   if (colStyle->mColumnWidth.GetUnit() == eStyleUnit_Coord) {
diff --git a/layout/generic/nsFrame.cpp b/layout/generic/nsFrame.cpp
index bd96f213b0..a531dea07f 100644
--- a/layout/generic/nsFrame.cpp
+++ b/layout/generic/nsFrame.cpp
@@ -4515,68 +4515,44 @@ nsIFrame::InlinePrefISizeData::ForceBreak()
   mSkipWhitespace = true;
 }
 
-static void
-AddCoord(const nsStyleCoord& aStyle,
-         nsIFrame* aFrame,
-         nscoord* aCoord, float* aPercent,
-         bool aClampNegativeToZero)
-{
-  switch (aStyle.GetUnit()) {
-    case eStyleUnit_Coord: {
-      NS_ASSERTION(!aClampNegativeToZero || aStyle.GetCoordValue() >= 0,
-                   "unexpected negative value");
-      *aCoord += aStyle.GetCoordValue();
-      return;
-    }
-    case eStyleUnit_Percent: {
-      NS_ASSERTION(!aClampNegativeToZero || aStyle.GetPercentValue() >= 0.0f,
-                   "unexpected negative value");
-      *aPercent += aStyle.GetPercentValue();
-      return;
-    }
-    case eStyleUnit_Calc: {
-      const nsStyleCoord::Calc *calc = aStyle.GetCalcValue();
-      if (aClampNegativeToZero) {
-        // This is far from ideal when one is negative and one is positive.
-        *aCoord += std::max(calc->mLength, 0);
-        *aPercent += std::max(calc->mPercent, 0.0f);
-      } else {
-        *aCoord += calc->mLength;
-        *aPercent += calc->mPercent;
-      }
-      return;
-    }
-    default: {
-      return;
-    }
+static nscoord
+ResolveMargin(const nsStyleCoord& aStyle, nscoord aPercentageBasis)
+{
+  if (aStyle.GetUnit() == eStyleUnit_Auto) {
+    return nscoord(0);
   }
+  return nsLayoutUtils::ResolveToLength<false>(aStyle, aPercentageBasis);
+}
+
+static nscoord
+ResolvePadding(const nsStyleCoord& aStyle, nscoord aPercentageBasis)
+{
+  return nsLayoutUtils::ResolveToLength<true>(aStyle, aPercentageBasis);
 }
 
 static nsIFrame::IntrinsicISizeOffsetData
-IntrinsicSizeOffsets(nsIFrame* aFrame, bool aForISize)
+IntrinsicSizeOffsets(nsIFrame* aFrame, nscoord aPercentageBasis, bool aForISize)
 {
   nsIFrame::IntrinsicISizeOffsetData result;
   WritingMode wm = aFrame->GetWritingMode();
-  const nsStyleMargin* styleMargin = aFrame->StyleMargin();
+  const auto& margin = aFrame->StyleMargin()->mMargin;
   bool verticalAxis = aForISize == wm.IsVertical();
-  AddCoord(verticalAxis ? styleMargin->mMargin.GetTop()
-                        : styleMargin->mMargin.GetLeft(),
-           aFrame, &result.hMargin, &result.hPctMargin,
-           false);
-  AddCoord(verticalAxis ? styleMargin->mMargin.GetBottom()
-                        : styleMargin->mMargin.GetRight(),
-           aFrame, &result.hMargin, &result.hPctMargin,
-           false);
-
-  const nsStylePadding* stylePadding = aFrame->StylePadding();
-  AddCoord(verticalAxis ? stylePadding->mPadding.GetTop()
-                        : stylePadding->mPadding.GetLeft(),
-           aFrame, &result.hPadding, &result.hPctPadding,
-           true);
-  AddCoord(verticalAxis ? stylePadding->mPadding.GetBottom()
-                        : stylePadding->mPadding.GetRight(),
-           aFrame, &result.hPadding, &result.hPctPadding,
-           true);
+  if (verticalAxis) {
+    result.hMargin += ResolveMargin(margin.GetTop(), aPercentageBasis);
+    result.hMargin += ResolveMargin(margin.GetBottom(), aPercentageBasis);
+  } else {
+    result.hMargin += ResolveMargin(margin.GetLeft(), aPercentageBasis);
+    result.hMargin += ResolveMargin(margin.GetRight(), aPercentageBasis);
+  }
+
+  const auto& padding = aFrame->StylePadding()->mPadding;
+  if (verticalAxis) {
+    result.hPadding += ResolvePadding(padding.GetTop(), aPercentageBasis);
+    result.hPadding += ResolvePadding(padding.GetBottom(), aPercentageBasis);
+  } else {
+    result.hPadding += ResolvePadding(padding.GetLeft(), aPercentageBasis);
+    result.hPadding += ResolvePadding(padding.GetRight(), aPercentageBasis);
+  }
 
   const nsStyleBorder* styleBorder = aFrame->StyleBorder();
   if (verticalAxis) {
@@ -4606,22 +4582,21 @@ IntrinsicSizeOffsets(nsIFrame* aFrame, bool aForISize)
       result.hPadding =
         presContext->DevPixelsToAppUnits(verticalAxis ? padding.TopBottom()
                                                       : padding.LeftRight());
-      result.hPctPadding = 0;
     }
   }
   return result;
 }
 
 /* virtual */ nsIFrame::IntrinsicISizeOffsetData
-nsFrame::IntrinsicISizeOffsets()
+nsFrame::IntrinsicISizeOffsets(nscoord aPercentageBasis)
 {
-  return IntrinsicSizeOffsets(this, true);
+  return IntrinsicSizeOffsets(this, aPercentageBasis, true);
 }
 
 nsIFrame::IntrinsicISizeOffsetData
-nsIFrame::IntrinsicBSizeOffsets()
+nsIFrame::IntrinsicBSizeOffsets(nscoord aPercentageBasis)
 {
-  return IntrinsicSizeOffsets(this, false);
+  return IntrinsicSizeOffsets(this, aPercentageBasis, false);
 }
 
 /* virtual */ IntrinsicSize
diff --git a/layout/generic/nsFrame.h b/layout/generic/nsFrame.h
index af1c95ef29..439e398562 100644
--- a/layout/generic/nsFrame.h
+++ b/layout/generic/nsFrame.h
@@ -261,7 +261,8 @@ public:
                                  InlineMinISizeData *aData) override;
   virtual void AddInlinePrefISize(nsRenderingContext *aRenderingContext,
                                   InlinePrefISizeData *aData) override;
-  virtual IntrinsicISizeOffsetData IntrinsicISizeOffsets() override;
+  IntrinsicISizeOffsetData
+  IntrinsicISizeOffsets(nscoord aPercentageBasis = NS_UNCONSTRAINEDSIZE) override;
   virtual mozilla::IntrinsicSize GetIntrinsicSize() override;
   virtual nsSize GetIntrinsicRatio() override;
 
diff --git a/layout/generic/nsGridContainerFrame.cpp b/layout/generic/nsGridContainerFrame.cpp
index 054f012978..959061e334 100644
--- a/layout/generic/nsGridContainerFrame.cpp
+++ b/layout/generic/nsGridContainerFrame.cpp
@@ -8,8 +8,8 @@
 
 #include "nsGridContainerFrame.h"
 
-#include <algorithm> // for std::stable_sort
 #include <limits>
+#include <stdlib.h> // for div()
 #include "mozilla/CSSAlignUtils.h"
 #include "mozilla/dom/GridBinding.h"
 #include "mozilla/Function.h"
@@ -127,43 +127,6 @@ ResolveToDefiniteSize(const nsStyleCoord& aCoord, nscoord aPercentBasis)
                   nsRuleNode::ComputeCoordPercentCalc(aCoord, aPercentBasis));
 }
 
-static bool
-GetPercentSizeParts(const nsStyleCoord& aCoord, nscoord* aLength, float* aPercent)
-{
-  switch (aCoord.GetUnit()) {
-    case eStyleUnit_Percent:
-      *aLength = 0;
-      *aPercent = aCoord.GetPercentValue();
-      return true;
-    case eStyleUnit_Calc: {
-      nsStyleCoord::Calc* calc = aCoord.GetCalcValue();
-      *aLength = calc->mLength;
-      *aPercent = calc->mPercent;
-      return true;
-    }
-    default:
-      return false;
-  }
-}
-
-static void
-ResolvePercentSizeParts(const nsStyleCoord& aCoord, nscoord aPercentBasis,
-                        nscoord* aLength, float* aPercent)
-{
-  MOZ_ASSERT(aCoord.IsCoordPercentCalcUnit());
-  if (aPercentBasis != NS_UNCONSTRAINEDSIZE) {
-    *aLength = std::max(nscoord(0),
-                        nsRuleNode::ComputeCoordPercentCalc(aCoord,
-                                                            aPercentBasis));
-    *aPercent = 0.0f;
-    return;
-  }
-  if (!GetPercentSizeParts(aCoord, aLength, aPercent)) {
-    *aLength = aCoord.ToLength();
-    *aPercent = 0.0f;
-  }
-}
-
 // Synthesize a baseline from a border box.  For an alphabetical baseline
 // this is the end edge of the border box.  For a central baseline it's
 // the center of the border box.
@@ -1172,7 +1135,7 @@ struct nsGridContainerFrame::TrackSizingFunctions
       return 1;
     }
     nscoord repeatTrackSize = 0;
-    // Note that the repeat() track size is included in |sum| in this loop.
+    // Note that one repeat() track size is included in |sum| in this loop.
     nscoord sum = 0;
     const nscoord percentBasis = aSize;
     for (uint32_t i = 0; i < numTracks; ++i) {
@@ -1189,54 +1152,31 @@ struct nsGridContainerFrame::TrackSizingFunctions
       }
       nscoord trackSize = ::ResolveToDefiniteSize(*coord, percentBasis);
       if (i == mRepeatAutoStart) {
-        if (percentBasis != NS_UNCONSTRAINEDSIZE) {
-          // Use a minimum 1px for the repeat() track-size.
-          if (trackSize < AppUnitsPerCSSPixel()) {
-            trackSize = AppUnitsPerCSSPixel();
-          }
+        // Use a minimum 1px for the repeat() track-size.
+        if (trackSize < AppUnitsPerCSSPixel()) {
+          trackSize = AppUnitsPerCSSPixel();
         }
         repeatTrackSize = trackSize;
       }
       sum += trackSize;
     }
-    nscoord gridGap;
-    float percentSum = 0.0f;
-    float gridGapPercent;
-    ResolvePercentSizeParts(aGridGap, percentBasis, &gridGap, &gridGapPercent);
+    nscoord gridGap = nsLayoutUtils::ResolveGapToLength(aGridGap, aSize);
     if (numTracks > 1) {
       // Add grid-gaps for all the tracks including the repeat() track.
       sum += gridGap * (numTracks - 1);
-      percentSum = gridGapPercent * (numTracks - 1);
     }
     // Calculate the max number of tracks that fits without overflow.
     nscoord available = maxFill != NS_UNCONSTRAINEDSIZE ? maxFill : aMinSize;
-    nscoord size = nsLayoutUtils::AddPercents(sum, percentSum);
-    if (available - size < 0) {
+    nscoord spaceToFill = available - sum;
+    if (spaceToFill <= 0) {
       // "if any number of repetitions would overflow, then 1 repetition"
       return 1;
     }
-    uint32_t numRepeatTracks = 1;
-    bool exactFit = false;
-    while (true) {
-      sum += gridGap + repeatTrackSize;
-      percentSum += gridGapPercent;
-      nscoord newSize = nsLayoutUtils::AddPercents(sum, percentSum);
-      if (newSize <= size) {
-        // Adding more repeat-tracks won't make forward progress.
-        return numRepeatTracks;
-      }
-      size = newSize;
-      nscoord remaining = available - size;
-      exactFit = remaining == 0;
-      if (remaining >= 0) {
-        ++numRepeatTracks;
-      }
-      if (remaining <= 0) {
-        break;
-      }
-    }
-
-    if (!exactFit && maxFill == NS_UNCONSTRAINEDSIZE) {
+    // Calculate the max number of tracks that fits without overflow.
+    div_t q = div(spaceToFill, repeatTrackSize + gridGap);
+    // The +1 here is for the one repeat track we already accounted for above.
+    uint32_t numRepeatTracks = q.quot + 1;
+    if (q.rem != 0 && maxFill == NS_UNCONSTRAINEDSIZE) {
       // "Otherwise, if the grid container has a definite min size in
       // the relevant axis, the number of repetitions is the largest possible
       // positive integer that fulfills that minimum requirement."
@@ -1882,13 +1822,6 @@ struct nsGridContainerFrame::Tracks
                            WritingMode            aWM,
                            const LogicalSize&     aContainerSize);
 
-  /**
-   * Return the intrinsic size by back-computing percentages as:
-   * IntrinsicSize = SumOfCoordSizes / (1 - SumOfPercentages).
-   */
-  nscoord BackComputedIntrinsicSize(const TrackSizingFunctions& aFunctions,
-                                    const nsStyleCoord& aGridGap) const;
-
   nscoord GridLineEdge(uint32_t aLine, GridLineSide aSide) const
   {
     if (MOZ_UNLIKELY(mSizes.IsEmpty())) {
@@ -2198,11 +2131,10 @@ struct MOZ_STACK_CLASS nsGridContainerFrame::GridReflowInput
   }
 
   /**
-   * Calculate our track sizes.  If the given aContentBox block-axis size is
-   * unconstrained, it is assigned to the resulting intrinsic block-axis size.
+   * Calculate our track sizes.
    */
   void CalculateTrackSizes(const Grid&        aGrid,
-                           LogicalSize&       aContentBox,
+                           const LogicalSize& aContentBox,
                            SizingConstraint   aConstraint);
 
   /**
@@ -2688,7 +2620,7 @@ struct MOZ_STACK_CLASS nsGridContainerFrame::Grid
 void
 nsGridContainerFrame::GridReflowInput::CalculateTrackSizes(
   const Grid&        aGrid,
-  LogicalSize&       aContentBox,
+  const LogicalSize& aContentBox,
   SizingConstraint   aConstraint)
 {
   mCols.Initialize(mColFunctions, mGridStyle->mGridColumnGap,
@@ -2706,12 +2638,6 @@ nsGridContainerFrame::GridReflowInput::CalculateTrackSizes(
   mRows.CalculateSizes(*this, mGridItems, mRowFunctions,
                        aContentBox.BSize(mWM), &GridArea::mRows,
                        aConstraint);
-  if (aContentBox.BSize(mWM) == NS_AUTOHEIGHT) {
-    aContentBox.BSize(mWM) =
-      mRows.BackComputedIntrinsicSize(mRowFunctions, mGridStyle->mGridRowGap);
-    mRows.mGridGap =
-      ::ResolveToDefiniteSize(mGridStyle->mGridRowGap, aContentBox.BSize(mWM));
-  }
 }
 
 /**
@@ -3813,7 +3739,7 @@ nsGridContainerFrame::Tracks::Initialize(
                                         aFunctions.MinSizingFor(i),
                                         aFunctions.MaxSizingFor(i));
   }
-  mGridGap = ::ResolveToDefiniteSize(aGridGap, aContentBoxSize);
+  mGridGap = nsLayoutUtils::ResolveGapToLength(aGridGap, aContentBoxSize);
   mContentBoxSize = aContentBoxSize;
 }
 
@@ -3894,8 +3820,7 @@ ContentContribution(const GridItemInfo&       aGridItem,
   PhysicalAxis axis(aCBWM.PhysicalAxis(aAxis));
   nscoord size = nsLayoutUtils::IntrinsicForAxis(axis, aRC, child, aConstraint,
                    aPercentageBasis,
-                   aFlags | nsLayoutUtils::BAIL_IF_REFLOW_NEEDED |
-                            nsLayoutUtils::ADD_PERCENTS,
+                   aFlags | nsLayoutUtils::BAIL_IF_REFLOW_NEEDED,
                    aMinSizeClamp);
   if (size == NS_INTRINSIC_WIDTH_UNKNOWN) {
     // We need to reflow the child to find its BSize contribution.
@@ -3932,15 +3857,7 @@ ContentContribution(const GridItemInfo&       aGridItem,
     LogicalSize availableSize(childWM, availISize, availBSize);
     size = ::MeasuringReflow(child, aState.mReflowInput, aRC, availableSize,
                              cbSize, iMinSizeClamp, bMinSizeClamp);
-    nsIFrame::IntrinsicISizeOffsetData offsets = child->IntrinsicBSizeOffsets();
-    size += offsets.hMargin;
-    auto percent = offsets.hPctMargin;
-    if (availBSize == NS_UNCONSTRAINEDSIZE) {
-      // We always want to add in percent padding too, unless we already did so
-      // using a resolved column size above.
-      percent += offsets.hPctPadding;
-    }
-    size = nsLayoutUtils::AddPercents(size, percent);
+    size += child->GetLogicalUsedMargin(childWM).BStartEnd(childWM);
     nscoord overflow = size - aMinSizeClamp;
     if (MOZ_UNLIKELY(overflow > 0)) {
       nscoord contentSize = child->ContentBSize(childWM);
@@ -4045,6 +3962,10 @@ MinSize(const GridItemInfo&    aGridItem,
     return s;
   }
 
+  if (aCache->mPercentageBasis.isNothing()) {
+    aCache->mPercentageBasis.emplace(aState.PercentageBasisFor(aAxis, aGridItem));
+  }
+
   // https://drafts.csswg.org/css-grid/#min-size-auto
   // This calculates the min-content contribution from either a definite
   // min-width (or min-height depending on aAxis), or the "specified /
@@ -4058,7 +3979,8 @@ MinSize(const GridItemInfo&    aGridItem,
              "baseline offset should be zero when not baseline-aligned");
   nscoord sz = aGridItem.mBaselineOffset[aAxis] +
     nsLayoutUtils::MinSizeContributionForAxis(axis, aRC, child,
-                                              nsLayoutUtils::MIN_ISIZE);
+                                              nsLayoutUtils::MIN_ISIZE,
+                                              *aCache->mPercentageBasis);
   const nsStyleCoord& style = axis == eAxisHorizontal ? stylePos->mMinWidth
                                                       : stylePos->mMinHeight;
   auto unit = style.GetUnit();
@@ -4067,9 +3989,6 @@ MinSize(const GridItemInfo&    aGridItem,
        child->StyleDisplay()->mOverflowX == NS_STYLE_OVERFLOW_VISIBLE)) {
     // Now calculate the "content size" part and return whichever is smaller.
     MOZ_ASSERT(unit != eStyleUnit_Enumerated || sz == NS_UNCONSTRAINEDSIZE);
-    if (aCache->mPercentageBasis.isNothing()) {
-      aCache->mPercentageBasis.emplace(aState.PercentageBasisFor(aAxis, aGridItem));
-    }
     sz = std::min(sz, ContentContribution(aGridItem, aState, aRC, aCBWM, aAxis,
                                           aCache->mPercentageBasis,
                                           nsLayoutUtils::MIN_ISIZE,
@@ -5097,36 +5016,6 @@ nsGridContainerFrame::Tracks::AlignJustifyContent(
   MOZ_ASSERT(!roundingError, "we didn't distribute all rounding error?");
 }
 
-nscoord
-nsGridContainerFrame::Tracks::BackComputedIntrinsicSize(
-  const TrackSizingFunctions& aFunctions,
-  const nsStyleCoord& aGridGap) const
-{
-  // Sum up the current sizes (where percentage tracks were treated as 'auto')
-  // in 'size'.
-  nscoord size = 0;
-  for (size_t i = 0, len = mSizes.Length(); i < len; ++i) {
-    size += mSizes[i].mBase;
-  }
-
-  // Add grid-gap contributions to 'size' and calculate a 'percent' sum.
-  float percent = 0.0f;
-  size_t numTracks = mSizes.Length();
-  if (numTracks > 1) {
-    const size_t gridGapCount = numTracks - 1;
-    nscoord gridGapLength;
-    float gridGapPercent;
-    if (::GetPercentSizeParts(aGridGap, &gridGapLength, &gridGapPercent)) {
-      percent = gridGapCount * gridGapPercent;
-    } else {
-      gridGapLength = aGridGap.ToLength();
-    }
-    size += gridGapCount * gridGapLength;
-  }
-
-  return std::max(0, nsLayoutUtils::AddPercents(size, percent));
-}
-
 void
 nsGridContainerFrame::LineRange::ToPositionAndLength(
   const nsTArray<TrackSize>& aTrackSizes, nscoord* aPos, nscoord* aLength) const
@@ -6292,7 +6181,7 @@ nsGridContainerFrame::Reflow(nsPresContext*           aPresContext,
   LogicalSize computedSize(wm, computedISize, computedBSize);
 
   nscoord consumedBSize = 0;
-  nscoord bSize;
+  nscoord bSize = 0;
   if (!prevInFlow) {
     Grid grid;
     grid.PlaceGridItems(gridReflowInput, aReflowInput.ComputedMinSize(),
@@ -6300,7 +6189,12 @@ nsGridContainerFrame::Reflow(nsPresContext*           aPresContext,
 
     gridReflowInput.CalculateTrackSizes(grid, computedSize,
                                         SizingConstraint::eNoConstraint);
-    bSize = computedSize.BSize(wm);
+    // Note: we can't use GridLineEdge here since we haven't calculated
+    // the rows' mPosition yet (happens in AlignJustifyContent below).
+    for (const auto& sz : gridReflowInput.mRows.mSizes) {
+      bSize += sz.mBase;
+    }
+    bSize += gridReflowInput.mRows.SumOfGridGaps();
   } else {
     consumedBSize = GetConsumedBSize();
     gridReflowInput.InitializeForContinuation(this, consumedBSize);
@@ -6699,8 +6593,14 @@ nsGridContainerFrame::IntrinsicISize(nsRenderingContext* aRenderingContext,
   state.mCols.CalculateSizes(state, state.mGridItems, state.mColFunctions,
                              NS_UNCONSTRAINEDSIZE, &GridArea::mCols,
                              constraint);
-  return state.mCols.BackComputedIntrinsicSize(state.mColFunctions,
-                                               state.mGridStyle->mGridColumnGap);
+  state.mCols.mGridGap =
+    nsLayoutUtils::ResolveGapToLength(state.mGridStyle->mGridColumnGap,
+                                      NS_UNCONSTRAINEDSIZE);
+  nscoord length = 0;
+  for (const TrackSize& sz : state.mCols.mSizes) {
+    length += sz.mBase;
+  }
+  return length + state.mCols.SumOfGridGaps();
 }
 
 nscoord
diff --git a/layout/generic/nsIFrame.h b/layout/generic/nsIFrame.h
index ec35684832..57f5c460c2 100644
--- a/layout/generic/nsIFrame.h
+++ b/layout/generic/nsIFrame.h
@@ -25,6 +25,7 @@
 
 #include "CaretAssociationHint.h"
 #include "FrameProperties.h"
+#include "LayoutConstants.h"
 #include "mozilla/layout/FrameChildList.h"
 #include "mozilla/Maybe.h"
 #include "mozilla/WritingModes.h"
@@ -130,30 +131,12 @@ typedef uint32_t nsSplittableType;
 #define NS_FRAME_IS_NOT_SPLITTABLE(type)\
   (0 == ((type) & NS_FRAME_SPLITTABLE))
 
-#define NS_INTRINSIC_WIDTH_UNKNOWN nscoord_MIN
-
 //----------------------------------------------------------------------
 
 #define NS_SUBTREE_DIRTY(_frame)  \
   (((_frame)->GetStateBits() &      \
     (NS_FRAME_IS_DIRTY | NS_FRAME_HAS_DIRTY_CHILDREN)) != 0)
 
-/**
- * Constant used to indicate an unconstrained size.
- *
- * @see #Reflow()
- */
-#define NS_UNCONSTRAINEDSIZE NS_MAXSIZE
-
-#define NS_INTRINSICSIZE    NS_UNCONSTRAINEDSIZE
-#define NS_AUTOHEIGHT       NS_UNCONSTRAINEDSIZE
-// +1 is to avoid clamped huge margin values being processed as auto margins
-#define NS_AUTOMARGIN       (NS_UNCONSTRAINEDSIZE + 1)
-#define NS_AUTOOFFSET       NS_UNCONSTRAINEDSIZE
-// NOTE: there are assumptions all over that these have the same value, namely NS_UNCONSTRAINEDSIZE
-//       if any are changed to be a value other than NS_UNCONSTRAINEDSIZE
-//       at least update AdjustComputedHeight/Width and test ad nauseum
-
 // 1 million CSS pixels less than our max app unit measure.
 // For reflowing with an "infinite" available inline space per [css-sizing].
 // (reflowing with an NS_UNCONSTRAINEDSIZE available inline size isn't allowed
@@ -2050,23 +2033,27 @@ public:
   /**
    * Return the horizontal components of padding, border, and margin
    * that contribute to the intrinsic width that applies to the parent.
+   * @param aPercentageBasis the percentage basis to use for padding/margin -
+   *   i.e. the Containing Block's inline-size
    */
   struct IntrinsicISizeOffsetData {
     nscoord hPadding, hBorder, hMargin;
-    float hPctPadding, hPctMargin;
 
     IntrinsicISizeOffsetData()
       : hPadding(0), hBorder(0), hMargin(0)
-      , hPctPadding(0.0f), hPctMargin(0.0f)
     {}
   };
-  virtual IntrinsicISizeOffsetData IntrinsicISizeOffsets() = 0;
+  virtual IntrinsicISizeOffsetData
+  IntrinsicISizeOffsets(nscoord aPercentageBasis = NS_UNCONSTRAINEDSIZE) = 0;
 
   /**
    * Return the bsize components of padding, border, and margin
    * that contribute to the intrinsic width that applies to the parent.
+   * @param aPercentageBasis the percentage basis to use for padding/margin -
+   *   i.e. the Containing Block's inline-size
    */
-  IntrinsicISizeOffsetData IntrinsicBSizeOffsets();
+  IntrinsicISizeOffsetData
+  IntrinsicBSizeOffsets(nscoord aPercentageBasis = NS_UNCONSTRAINEDSIZE);
 
   virtual mozilla::IntrinsicSize GetIntrinsicSize() = 0;
 
diff --git a/layout/style/nsCSSPropList.h b/layout/style/nsCSSPropList.h
index 2049f70e88..07db6d3ddc 100644
--- a/layout/style/nsCSSPropList.h
+++ b/layout/style/nsCSSPropList.h
@@ -1499,7 +1499,7 @@ CSS_PROP_COLUMN(
     CSS_PROPERTY_PARSE_VALUE |
         CSS_PROPERTY_VALUE_NONNEGATIVE,
     "",
-    VARIANT_HL | VARIANT_NORMAL | VARIANT_CALC,
+    VARIANT_HLP | VARIANT_NORMAL | VARIANT_CALC,
     nullptr,
     offsetof(nsStyleColumn, mColumnGap),
     eStyleAnimType_Coord)
diff --git a/layout/style/nsStyleStruct.h b/layout/style/nsStyleStruct.h
index c8182b8f14..b257c6bb54 100644
--- a/layout/style/nsStyleStruct.h
+++ b/layout/style/nsStyleStruct.h
@@ -3495,7 +3495,7 @@ struct MOZ_NEEDS_MEMMOVABLE_MEMBERS nsStyleColumn
 
   uint32_t     mColumnCount; // [reset] see nsStyleConsts.h
   nsStyleCoord mColumnWidth; // [reset] coord, auto
-  nsStyleCoord mColumnGap;   // [reset] coord, normal
+  nsStyleCoord mColumnGap;   // [reset] <length-percentage> | normal
 
   mozilla::StyleComplexColor mColumnRuleColor; // [reset]
   uint8_t      mColumnRuleStyle;  // [reset]
diff --git a/layout/style/test/property_database.js b/layout/style/test/property_database.js
index 272931c15e..c75f7b498f 100644
--- a/layout/style/test/property_database.js
+++ b/layout/style/test/property_database.js
@@ -1438,7 +1438,7 @@ var gCSSProperties = {
     inherited: false,
     type: CSS_TYPE_LONGHAND,
     initial_values: [ "normal", "1em", "calc(-2em + 3em)" ],
-    other_values: [ "2px", "4em",
+    other_values: [ "2px", "1em", "4em", "3%", "calc(3%)", "calc(1em - 3%)",
       "calc(2px)",
       "calc(-2px)",
       "calc(0px)",
@@ -1448,7 +1448,7 @@ var gCSSProperties = {
       "calc(25px*3)",
       "calc(3*25px + 5em)",
     ],
-    invalid_values: [ "3%", "-1px", "4" ]
+    invalid_values: [ "-3%", "-1px", "4" ]
   },
   "-moz-column-gap": {
     domProp: "MozColumnGap",
diff --git a/layout/tables/nsTableCellFrame.cpp b/layout/tables/nsTableCellFrame.cpp
index 316a966134..dea82ea591 100644
--- a/layout/tables/nsTableCellFrame.cpp
+++ b/layout/tables/nsTableCellFrame.cpp
@@ -796,12 +796,12 @@ nsTableCellFrame::GetPrefISize(nsRenderingContext *aRenderingContext)
 }
 
 /* virtual */ nsIFrame::IntrinsicISizeOffsetData
-nsTableCellFrame::IntrinsicISizeOffsets()
+nsTableCellFrame::IntrinsicISizeOffsets(nscoord aPercentageBasis)
 {
-  IntrinsicISizeOffsetData result = nsContainerFrame::IntrinsicISizeOffsets();
+  IntrinsicISizeOffsetData result =
+    nsContainerFrame::IntrinsicISizeOffsets(aPercentageBasis);
 
   result.hMargin = 0;
-  result.hPctMargin = 0;
 
   WritingMode wm = GetWritingMode();
   result.hBorder = GetBorderWidth(wm).IStartEnd(wm);
diff --git a/layout/tables/nsTableCellFrame.h b/layout/tables/nsTableCellFrame.h
index 6717e1b70d..2408098507 100644
--- a/layout/tables/nsTableCellFrame.h
+++ b/layout/tables/nsTableCellFrame.h
@@ -118,7 +118,8 @@ public:
 
   virtual nscoord GetMinISize(nsRenderingContext *aRenderingContext) override;
   virtual nscoord GetPrefISize(nsRenderingContext *aRenderingContext) override;
-  virtual IntrinsicISizeOffsetData IntrinsicISizeOffsets() override;
+  IntrinsicISizeOffsetData IntrinsicISizeOffsets(nscoord aPercentageBasis =
+                                                 NS_UNCONSTRAINEDSIZE) override;
 
   virtual void Reflow(nsPresContext*      aPresContext,
                       ReflowOutput& aDesiredSize,
diff --git a/layout/tables/nsTableFrame.cpp b/layout/tables/nsTableFrame.cpp
index b9b6ca5fe5..272a77406a 100644
--- a/layout/tables/nsTableFrame.cpp
+++ b/layout/tables/nsTableFrame.cpp
@@ -1564,16 +1564,15 @@ nsTableFrame::GetPrefISize(nsRenderingContext *aRenderingContext)
 }
 
 /* virtual */ nsIFrame::IntrinsicISizeOffsetData
-nsTableFrame::IntrinsicISizeOffsets()
+nsTableFrame::IntrinsicISizeOffsets(nscoord aPercentageBasis)
 {
-  IntrinsicISizeOffsetData result = nsContainerFrame::IntrinsicISizeOffsets();
+  IntrinsicISizeOffsetData result =
+    nsContainerFrame::IntrinsicISizeOffsets(aPercentageBasis);
 
   result.hMargin = 0;
-  result.hPctMargin = 0;
 
   if (IsBorderCollapse()) {
     result.hPadding = 0;
-    result.hPctPadding = 0;
 
     WritingMode wm = GetWritingMode();
     LogicalMargin outerBC = GetIncludedOuterBCBorder(wm);
diff --git a/layout/tables/nsTableFrame.h b/layout/tables/nsTableFrame.h
index 7e56c28c17..c7b92d387e 100644
--- a/layout/tables/nsTableFrame.h
+++ b/layout/tables/nsTableFrame.h
@@ -324,7 +324,8 @@ public:
   // border to the results of these functions.
   virtual nscoord GetMinISize(nsRenderingContext *aRenderingContext) override;
   virtual nscoord GetPrefISize(nsRenderingContext *aRenderingContext) override;
-  virtual IntrinsicISizeOffsetData IntrinsicISizeOffsets() override;
+  IntrinsicISizeOffsetData IntrinsicISizeOffsets(nscoord aPercentageBasis =
+                                                 NS_UNCONSTRAINEDSIZE) override;
 
   virtual mozilla::LogicalSize
   ComputeSize(nsRenderingContext*         aRenderingContext,