Backed out changeset 1a951477dca5 (bug 1588743) for xpcshell failures at devtools/shared/tests/unit/test_css-properties-db.js on a CLOSED TREE

dom/base/Element.cpp

@@ -675,13 +675,15 @@ void Element::ScrollIntoView(const ScrollIntoViewOptions& aOptions) {
       MOZ_ASSERT_UNREACHABLE("Unexpected ScrollLogicalPosition value");
   }
 
-  ScrollFlags scrollFlags =
-      ScrollFlags::ScrollOverflowHidden | ScrollFlags::ScrollSnap;
+  ScrollFlags scrollFlags = ScrollFlags::ScrollOverflowHidden;
   if (aOptions.mBehavior == ScrollBehavior::Smooth) {
     scrollFlags |= ScrollFlags::ScrollSmooth;
   } else if (aOptions.mBehavior == ScrollBehavior::Auto) {
     scrollFlags |= ScrollFlags::ScrollSmoothAuto;
   }
+  if (StaticPrefs::layout_css_scroll_snap_v1_enabled()) {
+    scrollFlags |= ScrollFlags::ScrollSnap;
+  }
 
   presShell->ScrollContentIntoView(
       this, ScrollAxis(whereToScrollVertically, WhenToScroll::Always),

gfx/layers/FrameMetrics.h

@@ -721,6 +721,10 @@ struct ScrollSnapInfo {
   bool operator==(const ScrollSnapInfo& aOther) const {
     return mScrollSnapStrictnessX == aOther.mScrollSnapStrictnessX &&
            mScrollSnapStrictnessY == aOther.mScrollSnapStrictnessY &&
+           mScrollSnapIntervalX == aOther.mScrollSnapIntervalX &&
+           mScrollSnapIntervalY == aOther.mScrollSnapIntervalY &&
+           mScrollSnapDestination == aOther.mScrollSnapDestination &&
+           mScrollSnapCoordinates == aOther.mScrollSnapCoordinates &&
            mSnapPositionX == aOther.mSnapPositionX &&
            mSnapPositionY == aOther.mSnapPositionY &&
            mXRangeWiderThanSnapport == aOther.mXRangeWiderThanSnapport &&
@@ -750,6 +754,18 @@ struct ScrollSnapInfo {
   mozilla::StyleScrollSnapStrictness mScrollSnapStrictnessY =
       mozilla::StyleScrollSnapStrictness::None;
 
+  // The intervals derived from the scroll frame's scroll-snap-points.
+  Maybe<nscoord> mScrollSnapIntervalX;
+  Maybe<nscoord> mScrollSnapIntervalY;
+
+  // The scroll frame's scroll-snap-destination, in cooked form (to avoid
+  // shipping the raw style value over IPC).
+  nsPoint mScrollSnapDestination;
+
+  // The scroll-snap-coordinates of any descendant frames of the scroll frame,
+  // relative to the origin of the scrolled frame.
+  nsTArray<nsPoint> mScrollSnapCoordinates;
+
   // The scroll positions corresponding to scroll-snap-align values.
   nsTArray<nscoord> mSnapPositionX;
   nsTArray<nscoord> mSnapPositionY;

gfx/layers/apz/test/gtest/TestSnapping.cpp

@@ -29,8 +29,12 @@ TEST_F(APZCSnappingTester, Bug1265510) {
 
   ScrollSnapInfo snap;
   snap.mScrollSnapStrictnessY = StyleScrollSnapStrictness::Mandatory;
-  snap.mSnapPositionY.AppendElement(0 * AppUnitsPerCSSPixel());
-  snap.mSnapPositionY.AppendElement(100 * AppUnitsPerCSSPixel());
+  if (StaticPrefs::layout_css_scroll_snap_v1_enabled()) {
+    snap.mSnapPositionY.AppendElement(0 * AppUnitsPerCSSPixel());
+    snap.mSnapPositionY.AppendElement(100 * AppUnitsPerCSSPixel());
+  } else {
+    snap.mScrollSnapIntervalY = Some(100 * AppUnitsPerCSSPixel());
+  }
 
   ScrollMetadata metadata = root->GetScrollMetadata(0);
   metadata.SetSnapInfo(ScrollSnapInfo(snap));
@@ -101,8 +105,12 @@ TEST_F(APZCSnappingTester, Snap_After_Pinch) {
   ScrollSnapInfo snap;
   snap.mScrollSnapStrictnessY = StyleScrollSnapStrictness::Mandatory;
 
-  snap.mSnapPositionY.AppendElement(0 * AppUnitsPerCSSPixel());
-  snap.mSnapPositionY.AppendElement(100 * AppUnitsPerCSSPixel());
+  if (StaticPrefs::layout_css_scroll_snap_v1_enabled()) {
+    snap.mSnapPositionY.AppendElement(0 * AppUnitsPerCSSPixel());
+    snap.mSnapPositionY.AppendElement(100 * AppUnitsPerCSSPixel());
+  } else {
+    snap.mScrollSnapIntervalY = Some(100 * AppUnitsPerCSSPixel());
+  }
 
   // Save the scroll snap info on the root APZC.
   // Also mark the root APZC as "root content", since APZC only allows

gfx/layers/apz/test/gtest/TestSnappingOnMomentum.cpp

@@ -28,8 +28,12 @@ TEST_F(APZCSnappingOnMomentumTester, Snap_On_Momentum) {
   ScrollSnapInfo snap;
   snap.mScrollSnapStrictnessY = StyleScrollSnapStrictness::Mandatory;
 
-  snap.mSnapPositionY.AppendElement(0 * AppUnitsPerCSSPixel());
-  snap.mSnapPositionY.AppendElement(100 * AppUnitsPerCSSPixel());
+  if (StaticPrefs::layout_css_scroll_snap_v1_enabled()) {
+    snap.mSnapPositionY.AppendElement(0 * AppUnitsPerCSSPixel());
+    snap.mSnapPositionY.AppendElement(100 * AppUnitsPerCSSPixel());
+  } else {
+    snap.mScrollSnapIntervalY = Some(100 * AppUnitsPerCSSPixel());
+  }
 
   ScrollMetadata metadata = root->GetScrollMetadata(0);
   metadata.SetSnapInfo(ScrollSnapInfo(snap));

gfx/layers/apz/test/mochitest/test_group_scroll_snap.html

@@ -15,6 +15,7 @@ const prefs = [
   // the target APZC after each such movement.
   ["mousewheel.transaction.ignoremovedelay", 0],
   ["mousewheel.transaction.timeout", 0],
+  ["layout.css.scroll-snap-v1.enabled", true],
 ];
 
 const subtests = [

gfx/layers/ipc/LayersMessageUtils.h

@@ -322,6 +322,10 @@ struct ParamTraits<mozilla::layers::ScrollSnapInfo> {
   static void Write(Message* aMsg, const paramType& aParam) {
     WriteParam(aMsg, aParam.mScrollSnapStrictnessX);
     WriteParam(aMsg, aParam.mScrollSnapStrictnessY);
+    WriteParam(aMsg, aParam.mScrollSnapIntervalX);
+    WriteParam(aMsg, aParam.mScrollSnapIntervalY);
+    WriteParam(aMsg, aParam.mScrollSnapDestination);
+    WriteParam(aMsg, aParam.mScrollSnapCoordinates);
     WriteParam(aMsg, aParam.mSnapPositionX);
     WriteParam(aMsg, aParam.mSnapPositionY);
     WriteParam(aMsg, aParam.mXRangeWiderThanSnapport);
@@ -333,6 +337,10 @@ struct ParamTraits<mozilla::layers::ScrollSnapInfo> {
                    paramType* aResult) {
     return (ReadParam(aMsg, aIter, &aResult->mScrollSnapStrictnessX) &&
             ReadParam(aMsg, aIter, &aResult->mScrollSnapStrictnessY) &&
+            ReadParam(aMsg, aIter, &aResult->mScrollSnapIntervalX) &&
+            ReadParam(aMsg, aIter, &aResult->mScrollSnapIntervalY) &&
+            ReadParam(aMsg, aIter, &aResult->mScrollSnapDestination) &&
+            ReadParam(aMsg, aIter, &aResult->mScrollSnapCoordinates) &&
             ReadParam(aMsg, aIter, &aResult->mSnapPositionX) &&
             ReadParam(aMsg, aIter, &aResult->mSnapPositionY) &&
             ReadParam(aMsg, aIter, &aResult->mXRangeWiderThanSnapport) &&

layout/base/ScrollStyles.cpp

@@ -10,18 +10,59 @@
 
 namespace mozilla {
 
+void ScrollStyles::InitializeScrollSnapStrictness(
+    WritingMode aWritingMode, const nsStyleDisplay* aDisplay) {
+  mScrollSnapStrictnessX = StyleScrollSnapStrictness::None;
+  mScrollSnapStrictnessY = StyleScrollSnapStrictness::None;
+
+  if (aDisplay->mScrollSnapType.strictness == StyleScrollSnapStrictness::None) {
+    return;
+  }
+
+  switch (aDisplay->mScrollSnapType.axis) {
+    case StyleScrollSnapAxis::X:
+      mScrollSnapStrictnessX = aDisplay->mScrollSnapType.strictness;
+      break;
+    case StyleScrollSnapAxis::Y:
+      mScrollSnapStrictnessY = aDisplay->mScrollSnapType.strictness;
+      break;
+    case StyleScrollSnapAxis::Block:
+      if (aWritingMode.IsVertical()) {
+        mScrollSnapStrictnessX = aDisplay->mScrollSnapType.strictness;
+      } else {
+        mScrollSnapStrictnessY = aDisplay->mScrollSnapType.strictness;
+      }
+      break;
+    case StyleScrollSnapAxis::Inline:
+      if (aWritingMode.IsVertical()) {
+        mScrollSnapStrictnessY = aDisplay->mScrollSnapType.strictness;
+      } else {
+        mScrollSnapStrictnessX = aDisplay->mScrollSnapType.strictness;
+      }
+      break;
+    case StyleScrollSnapAxis::Both:
+      mScrollSnapStrictnessX = aDisplay->mScrollSnapType.strictness;
+      mScrollSnapStrictnessY = aDisplay->mScrollSnapType.strictness;
+      break;
+  }
+}
+
 ScrollStyles::ScrollStyles(WritingMode aWritingMode, StyleOverflow aH,
                            StyleOverflow aV, const nsStyleDisplay* aDisplay)
     : mHorizontal(aH),
       mVertical(aV),
       mOverscrollBehaviorX(aDisplay->mOverscrollBehaviorX),
-      mOverscrollBehaviorY(aDisplay->mOverscrollBehaviorY) {}
+      mOverscrollBehaviorY(aDisplay->mOverscrollBehaviorY) {
+  InitializeScrollSnapStrictness(aWritingMode, aDisplay);
+}
 
 ScrollStyles::ScrollStyles(WritingMode aWritingMode,
                            const nsStyleDisplay* aDisplay)
     : mHorizontal(aDisplay->mOverflowX),
       mVertical(aDisplay->mOverflowY),
       mOverscrollBehaviorX(aDisplay->mOverscrollBehaviorX),
-      mOverscrollBehaviorY(aDisplay->mOverscrollBehaviorY) {}
+      mOverscrollBehaviorY(aDisplay->mOverscrollBehaviorY) {
+  InitializeScrollSnapStrictness(aWritingMode, aDisplay);
+}
 
 }  // namespace mozilla

layout/base/ScrollStyles.h

@@ -16,31 +16,37 @@ struct nsStyleDisplay;
 
 namespace mozilla {
 
-// NOTE: Only styles that are propagated from the <body> should end up in this
-// class.
 struct ScrollStyles {
   // Always one of Scroll, Hidden, or Auto
   StyleOverflow mHorizontal;
   StyleOverflow mVertical;
-
-  // FIXME(emilio): we shouldn't propagate this.
+  // Always one of NS_STYLE_SCROLL_BEHAVIOR_AUTO or
+  // NS_STYLE_SCROLL_BEHAVIOR_SMOOTH
   StyleOverscrollBehavior mOverscrollBehaviorX;
   StyleOverscrollBehavior mOverscrollBehaviorY;
+  StyleScrollSnapStrictness mScrollSnapStrictnessX;
+  StyleScrollSnapStrictness mScrollSnapStrictnessY;
 
   ScrollStyles(StyleOverflow aH, StyleOverflow aV)
       : mHorizontal(aH),
         mVertical(aV),
         mOverscrollBehaviorX(StyleOverscrollBehavior::Auto),
-        mOverscrollBehaviorY(StyleOverscrollBehavior::Auto) {}
+        mOverscrollBehaviorY(StyleOverscrollBehavior::Auto),
+        mScrollSnapStrictnessX(StyleScrollSnapStrictness::None),
+        mScrollSnapStrictnessY(StyleScrollSnapStrictness::None) {}
 
   ScrollStyles(WritingMode aWritingMode, const nsStyleDisplay* aDisplay);
   ScrollStyles(WritingMode aWritingMode, StyleOverflow aH, StyleOverflow aV,
                const nsStyleDisplay* aDisplay);
+  void InitializeScrollSnapStrictness(WritingMode aWritingMode,
+                                      const nsStyleDisplay* aDisplay);
   bool operator==(const ScrollStyles& aStyles) const {
     return aStyles.mHorizontal == mHorizontal &&
            aStyles.mVertical == mVertical &&
            aStyles.mOverscrollBehaviorX == mOverscrollBehaviorX &&
-           aStyles.mOverscrollBehaviorY == mOverscrollBehaviorY;
+           aStyles.mOverscrollBehaviorY == mOverscrollBehaviorY &&
+           aStyles.mScrollSnapStrictnessX == mScrollSnapStrictnessX &&
+           aStyles.mScrollSnapStrictnessY == mScrollSnapStrictnessY;
   }
   bool operator!=(const ScrollStyles& aStyles) const {
     return !(*this == aStyles);

layout/generic/ScrollSnap.cpp

@@ -26,6 +26,10 @@ class CalcSnapPoints final {
                  const nsPoint& aDestination, const nsPoint& aStartPos);
   void AddHorizontalEdge(nscoord aEdge);
   void AddVerticalEdge(nscoord aEdge);
+  void AddHorizontalEdgeInterval(const nsRect& aScrollRange, nscoord aInterval,
+                                 nscoord aOffset);
+  void AddVerticalEdgeInterval(const nsRect& aScrollRange, nscoord aInterval,
+                               nscoord aOffset);
   void AddEdge(nscoord aEdge, nscoord aDestination, nscoord aStartPos,
                nscoord aScrollingDirection, nscoord* aBestEdge,
                nscoord* aSecondBestEdge, bool* aEdgeFound);
@@ -98,6 +102,22 @@ void CalcSnapPoints::AddVerticalEdge(nscoord aEdge) {
           &mBestEdge.x, &mSecondBestEdge.x, &mVerticalEdgeFound);
 }
 
+void CalcSnapPoints::AddHorizontalEdgeInterval(const nsRect& aScrollRange,
+                                               nscoord aInterval,
+                                               nscoord aOffset) {
+  AddEdgeInterval(aInterval, aScrollRange.y, aScrollRange.YMost(), aOffset,
+                  mDestination.y, mStartPos.y, mScrollingDirection.y,
+                  &mBestEdge.y, &mSecondBestEdge.y, &mHorizontalEdgeFound);
+}
+
+void CalcSnapPoints::AddVerticalEdgeInterval(const nsRect& aScrollRange,
+                                             nscoord aInterval,
+                                             nscoord aOffset) {
+  AddEdgeInterval(aInterval, aScrollRange.x, aScrollRange.XMost(), aOffset,
+                  mDestination.x, mStartPos.x, mScrollingDirection.x,
+                  &mBestEdge.x, &mSecondBestEdge.x, &mVerticalEdgeFound);
+}
+
 void CalcSnapPoints::AddEdge(nscoord aEdge, nscoord aDestination,
                              nscoord aStartPos, nscoord aScrollingDirection,
                              nscoord* aBestEdge, nscoord* aSecondBestEdge,
@@ -238,6 +258,19 @@ static void ProcessSnapPositions(CalcSnapPoints& aCalcSnapPoints,
   }
 }
 
+static void ProcessScrollSnapCoordinates(
+    CalcSnapPoints& aCalcSnapPoint,
+    const nsTArray<nsPoint>& aScrollSnapCoordinates,
+    const nsPoint& aScrollSnapDestination) {
+  for (nsPoint snapCoords : aScrollSnapCoordinates) {
+    // Make them relative to the scroll snap destination.
+    snapCoords -= aScrollSnapDestination;
+
+    aCalcSnapPoint.AddVerticalEdge(snapCoords.x);
+    aCalcSnapPoint.AddHorizontalEdge(snapCoords.y);
+  }
+}
+
 Maybe<nsPoint> ScrollSnapUtils::GetSnapPointForDestination(
     const ScrollSnapInfo& aSnapInfo, nsIScrollableFrame::ScrollUnit aUnit,
     const nsRect& aScrollRange, const nsPoint& aStartPos,
@@ -247,37 +280,55 @@ Maybe<nsPoint> ScrollSnapUtils::GetSnapPointForDestination(
     return Nothing();
   }
 
-  if (!aSnapInfo.HasSnapPositions()) {
+  if (StaticPrefs::layout_css_scroll_snap_v1_enabled() &&
+      !aSnapInfo.HasSnapPositions()) {
     return Nothing();
   }
 
   CalcSnapPoints calcSnapPoints(aUnit, aDestination, aStartPos);
 
-  ProcessSnapPositions(calcSnapPoints, aSnapInfo);
+  if (StaticPrefs::layout_css_scroll_snap_v1_enabled()) {
+    ProcessSnapPositions(calcSnapPoints, aSnapInfo);
 
-  // If the distance between the first and the second candidate snap points
-  // is larger than the snapport size and the snapport is covered by larger
-  // elements, any points inside the covering area should be valid snap
-  // points.
-  // https://drafts.csswg.org/css-scroll-snap-1/#snap-overflow
-  // NOTE: |aDestination| sometimes points outside of the scroll range, e.g.
-  // by the APZC fling, so for the overflow checks we need to clamp it.
-  nsPoint clampedDestination = aScrollRange.ClampPoint(aDestination);
-  for (auto range : aSnapInfo.mXRangeWiderThanSnapport) {
-    if (range.IsValid(clampedDestination.x, aSnapInfo.mSnapportSize.width) &&
-        calcSnapPoints.XDistanceBetweenBestAndSecondEdge() >
-            aSnapInfo.mSnapportSize.width) {
-      calcSnapPoints.AddVerticalEdge(clampedDestination.x);
-      break;
+    // If the distance between the first and the second candidate snap points
+    // is larger than the snapport size and the snapport is covered by larger
+    // elements, any points inside the covering area should be valid snap
+    // points.
+    // https://drafts.csswg.org/css-scroll-snap-1/#snap-overflow
+    // NOTE: |aDestination| sometimes points outside of the scroll range, e.g.
+    // by the APZC fling, so for the overflow checks we need to clamp it.
+    nsPoint clampedDestination = aScrollRange.ClampPoint(aDestination);
+    for (auto range : aSnapInfo.mXRangeWiderThanSnapport) {
+      if (range.IsValid(clampedDestination.x, aSnapInfo.mSnapportSize.width) &&
+          calcSnapPoints.XDistanceBetweenBestAndSecondEdge() >
+              aSnapInfo.mSnapportSize.width) {
+        calcSnapPoints.AddVerticalEdge(clampedDestination.x);
+        break;
+      }
     }
-  }
-  for (auto range : aSnapInfo.mYRangeWiderThanSnapport) {
-    if (range.IsValid(clampedDestination.y, aSnapInfo.mSnapportSize.height) &&
-        calcSnapPoints.YDistanceBetweenBestAndSecondEdge() >
-            aSnapInfo.mSnapportSize.height) {
-      calcSnapPoints.AddHorizontalEdge(clampedDestination.y);
-      break;
+    for (auto range : aSnapInfo.mYRangeWiderThanSnapport) {
+      if (range.IsValid(clampedDestination.y, aSnapInfo.mSnapportSize.height) &&
+          calcSnapPoints.YDistanceBetweenBestAndSecondEdge() >
+              aSnapInfo.mSnapportSize.height) {
+        calcSnapPoints.AddHorizontalEdge(clampedDestination.y);
+        break;
+      }
     }
+  } else {
+    nsPoint destPos = aSnapInfo.mScrollSnapDestination;
+
+    if (aSnapInfo.mScrollSnapIntervalX.isSome()) {
+      nscoord interval = aSnapInfo.mScrollSnapIntervalX.value();
+      calcSnapPoints.AddVerticalEdgeInterval(aScrollRange, interval, destPos.x);
+    }
+    if (aSnapInfo.mScrollSnapIntervalY.isSome()) {
+      nscoord interval = aSnapInfo.mScrollSnapIntervalY.value();
+      calcSnapPoints.AddHorizontalEdgeInterval(aScrollRange, interval,
+                                               destPos.y);
+    }
+
+    ProcessScrollSnapCoordinates(calcSnapPoints,
+                                 aSnapInfo.mScrollSnapCoordinates, destPos);
   }
 
   bool snapped = false;

layout/generic/nsGfxScrollFrame.cpp

@@ -2243,6 +2243,12 @@ void ScrollFrameHelper::ScrollTo(nsPoint aScrollPosition, ScrollMode aMode,
   ScrollToWithOrigin(aScrollPosition, aMode, aOrigin, aRange, aSnap);
 }
 
+static nsIScrollbarMediator::ScrollSnapMode DefaultSnapMode() {
+  return StaticPrefs::layout_css_scroll_snap_v1_enabled()
+             ? nsIScrollableFrame::ENABLE_SNAP
+             : nsIScrollableFrame::DISABLE_SNAP;
+}
+
 void ScrollFrameHelper::ScrollToCSSPixels(
     const CSSIntPoint& aScrollPosition, ScrollMode aMode,
     nsIScrollbarMediator::ScrollSnapMode aSnap, nsAtom* aOrigin) {
@@ -2250,7 +2256,7 @@ void ScrollFrameHelper::ScrollToCSSPixels(
   CSSIntPoint currentCSSPixels = GetScrollPositionCSSPixels();
   nsPoint pt = CSSPoint::ToAppUnits(aScrollPosition);
   if (aSnap == nsIScrollableFrame::DEFAULT) {
-    aSnap = nsIScrollableFrame::ENABLE_SNAP;
+    aSnap = DefaultSnapMode();
   }
 
   if (aOrigin == nullptr) {
@@ -4354,7 +4360,7 @@ void ScrollFrameHelper::ScrollByCSSPixels(
   nsPoint pt = CSSPoint::ToAppUnits(currentCSSPixels + aDelta);
 
   if (aSnap == nsIScrollableFrame::DEFAULT) {
-    aSnap = nsIScrollableFrame::ENABLE_SNAP;
+    aSnap = DefaultSnapMode();
   }
 
   if (aOrigin == nullptr) {
@@ -5481,12 +5487,18 @@ nsIFrame* ScrollFrameHelper::GetFrameForStyle() const {
 }
 
 bool ScrollFrameHelper::NeedsScrollSnap() const {
-  nsIFrame* scrollSnapFrame = GetFrameForStyle();
-  if (!scrollSnapFrame) {
-    return false;
+  if (StaticPrefs::layout_css_scroll_snap_v1_enabled()) {
+    nsIFrame* scrollSnapFrame = GetFrameForStyle();
+    if (!scrollSnapFrame) {
+      return false;
+    }
+    return scrollSnapFrame->StyleDisplay()->mScrollSnapType.strictness !=
+           StyleScrollSnapStrictness::None;
   }
-  return scrollSnapFrame->StyleDisplay()->mScrollSnapType.strictness !=
-         StyleScrollSnapStrictness::None;
+
+  ScrollStyles styles = GetScrollStylesFromFrame();
+  return styles.mScrollSnapStrictnessY != StyleScrollSnapStrictness::None ||
+         styles.mScrollSnapStrictnessX != StyleScrollSnapStrictness::None;
 }
 
 bool ScrollFrameHelper::IsScrollbarOnRight() const {
@@ -6847,6 +6859,8 @@ static void CollectScrollPositionsForSnap(
     nsIFrame* aFrame, nsIFrame* aScrolledFrame, const nsRect& aScrolledRect,
     const nsMargin& aScrollPadding, const Maybe<nsRect>& aSnapport,
     WritingMode aWritingModeOnScroller, ScrollSnapInfo& aSnapInfo) {
+  MOZ_ASSERT(StaticPrefs::layout_css_scroll_snap_v1_enabled());
+
   // Snap positions only affect the nearest ancestor scroll container on the
   // element's containing block chain.
   nsIScrollableFrame* sf = do_QueryFrame(aFrame);
@@ -6929,6 +6943,8 @@ nsMargin ScrollFrameHelper::GetScrollPadding() const {
 
 layers::ScrollSnapInfo ScrollFrameHelper::ComputeScrollSnapInfo(
     const Maybe<nsPoint>& aDestination) const {
+  MOZ_ASSERT(StaticPrefs::layout_css_scroll_snap_v1_enabled());
+
   ScrollSnapInfo result;
 
   nsIFrame* scrollSnapFrame = GetFrameForStyle();
@@ -6966,6 +6982,9 @@ layers::ScrollSnapInfo ScrollFrameHelper::ComputeScrollSnapInfo(
 
 layers::ScrollSnapInfo ScrollFrameHelper::GetScrollSnapInfo(
     const Maybe<nsPoint>& aDestination) const {
+  if (!StaticPrefs::layout_css_scroll_snap_v1_enabled()) {
+    return {};
+  }
   // TODO(botond): Should we cache it?
   return ComputeScrollSnapInfo(aDestination);
 }

layout/reftests/css-scroll-snap/reftest.list

@@ -1,2 +1,4 @@
+default-preferences pref(layout.css.scroll-snap-v1.enabled,true)
+
 == scroll-margin-on-anchor.html#target scroll-margin-on-anchor-ref.html
 == scroll-padding-on-anchor.html#target scroll-padding-on-anchor-ref.html

layout/style/test/property_database.js

@@ -7189,336 +7189,6 @@ var gCSSProperties = {
     other_values: ["smooth"],
     invalid_values: ["none", "1px"],
   },
-  "scroll-snap-type": {
-    domProp: "scrollSnapType",
-    inherited: false,
-    type: CSS_TYPE_LONGHAND,
-    initial_values: ["none"],
-    other_values: [
-      "both mandatory",
-      "y mandatory",
-      "inline proximity",
-      "both",
-      "x",
-      "y",
-      "block",
-      "inline",
-    ],
-    invalid_values: [
-      "auto",
-      "1px",
-      "x y",
-      "block mandatory inline",
-      "mandatory",
-      "proximity",
-      "mandatory inline",
-      "proximity both",
-      "mandatory x",
-      "proximity y",
-      "mandatory block",
-      "proximity mandatory",
-    ],
-  },
-  "scroll-snap-align": {
-    domProp: "scrollSnapAlign",
-    inherited: false,
-    type: CSS_TYPE_LONGHAND,
-    initial_values: ["none"],
-    other_values: [
-      "start",
-      "end",
-      "center",
-      "start none",
-      "center end",
-      "start start",
-    ],
-    invalid_values: ["auto", "start invalid", "start end center"],
-  },
-  "scroll-margin": {
-    domProp: "scrollMargin",
-    inherited: false,
-    type: CSS_TYPE_TRUE_SHORTHAND,
-    subproperties: [
-      "scroll-margin-top",
-      "scroll-margin-right",
-      "scroll-margin-bottom",
-      "scroll-margin-left",
-    ],
-    initial_values: ["0"],
-    other_values: [
-      "-10px",
-      "calc(2em + 3ex)",
-      "1px 2px",
-      "1px 2px 3px",
-      "1px 2px 3px 4px",
-    ],
-    invalid_values: ["auto", "20%", "-30%", "1px 2px 3px 4px 5px"],
-  },
-  "scroll-margin-top": {
-    domProp: "scrollMarginTop",
-    inherited: false,
-    type: CSS_TYPE_LONGHAND,
-    initial_values: ["0"],
-    other_values: ["-10px", "calc(2em + 3ex)"],
-    invalid_values: ["auto", "20%", "-30%", "1px 2px"],
-  },
-  "scroll-margin-right": {
-    domProp: "scrollMarginRight",
-    inherited: false,
-    type: CSS_TYPE_LONGHAND,
-    initial_values: ["0"],
-    other_values: ["-10px", "calc(2em + 3ex)"],
-    invalid_values: ["auto", "20%", "-30%", "1px 2px"],
-  },
-  "scroll-margin-bottom": {
-    domProp: "scrollMarginBottom",
-    inherited: false,
-    type: CSS_TYPE_LONGHAND,
-    initial_values: ["0"],
-    other_values: ["-10px", "calc(2em + 3ex)"],
-    invalid_values: ["auto", "20%", "-30%", "1px 2px"],
-  },
-  "scroll-margin-left": {
-    domProp: "scrollMarginLeft",
-    inherited: false,
-    type: CSS_TYPE_LONGHAND,
-    initial_values: ["0"],
-    other_values: ["-10px", "calc(2em + 3ex)"],
-    invalid_values: ["auto", "20%", "-30%", "1px 2px"],
-  },
-  "scroll-margin-inline": {
-    domProp: "scrollMarginInline",
-    inherited: false,
-    type: CSS_TYPE_TRUE_SHORTHAND,
-    subproperties: ["scroll-margin-inline-start", "scroll-margin-inline-end"],
-    initial_values: ["0"],
-    other_values: ["-10px", "calc(2em + 3ex)", "1px 2px"],
-    invalid_values: ["auto", "20%", "-30%", "1px 2px 3px"],
-  },
-  "scroll-margin-inline-start": {
-    domProp: "scrollMarginInlineStart",
-    inherited: false,
-    type: CSS_TYPE_LONGHAND,
-    logical: true,
-    initial_values: ["0"],
-    other_values: ["-10px", "calc(2em + 3ex)"],
-    invalid_values: ["auto", "20%", "-30%", "1px 2px"],
-  },
-  "scroll-margin-inline-end": {
-    domProp: "scrollMarginInlineEnd",
-    inherited: false,
-    type: CSS_TYPE_LONGHAND,
-    logical: true,
-    initial_values: ["0"],
-    other_values: ["-10px", "calc(2em + 3ex)"],
-    invalid_values: ["auto", "20%", "-30%", "1px 2px"],
-  },
-  "scroll-margin-block": {
-    domProp: "scrollMarginBlock",
-    inherited: false,
-    type: CSS_TYPE_TRUE_SHORTHAND,
-    subproperties: ["scroll-margin-block-start", "scroll-margin-block-end"],
-    initial_values: ["0"],
-    other_values: ["-10px", "calc(2em + 3ex)", "1px 2px"],
-    invalid_values: ["auto", "20%", "-30%", "1px 2px 3px"],
-  },
-  "scroll-margin-block-start": {
-    domProp: "scrollMarginBlockStart",
-    inherited: false,
-    type: CSS_TYPE_LONGHAND,
-    logical: true,
-    initial_values: ["0"],
-    other_values: ["-10px", "calc(2em + 3ex)"],
-    invalid_values: ["auto", "20%", "-30%", "1px 2px"],
-  },
-  "scroll-margin-block-end": {
-    domProp: "scrollMarginBlockEnd",
-    inherited: false,
-    type: CSS_TYPE_LONGHAND,
-    logical: true,
-    initial_values: ["0"],
-    other_values: ["-10px", "calc(2em + 3ex)"],
-    invalid_values: ["auto", "20%", "-30%", "1px 2px"],
-  },
-  "scroll-padding": {
-    domProp: "scrollPadding",
-    inherited: false,
-    type: CSS_TYPE_TRUE_SHORTHAND,
-    subproperties: [
-      "scroll-padding-top",
-      "scroll-padding-right",
-      "scroll-padding-bottom",
-      "scroll-padding-left",
-    ],
-    initial_values: ["auto"],
-    other_values: [
-      "10px",
-      "0",
-      "20%",
-      "calc(2em + 3ex)",
-      "1px 2px",
-      "1px 2px 3%",
-      "1px 2px 3% 4px",
-      "1px auto",
-    ],
-    invalid_values: ["20", "-20px"],
-  },
-  "scroll-padding-top": {
-    domProp: "scrollPaddingTop",
-    inherited: false,
-    type: CSS_TYPE_LONGHAND,
-    initial_values: ["auto"],
-    other_values: [
-      "0",
-      "10px",
-      "20%",
-      "calc(2em + 3ex)",
-      "calc(50% + 60px)",
-      "calc(-50px)",
-    ],
-    invalid_values: ["20", "-20px"],
-  },
-  "scroll-padding-right": {
-    domProp: "scrollPaddingRight",
-    inherited: false,
-    type: CSS_TYPE_LONGHAND,
-    initial_values: ["auto"],
-    other_values: [
-      "0",
-      "10px",
-      "20%",
-      "calc(2em + 3ex)",
-      "calc(50% + 60px)",
-      "calc(-50px)",
-    ],
-    invalid_values: ["20", "-20px"],
-  },
-  "scroll-padding-bottom": {
-    domProp: "scrollPaddingBottom",
-    inherited: false,
-    type: CSS_TYPE_LONGHAND,
-    initial_values: ["auto"],
-    other_values: [
-      "0",
-      "10px",
-      "20%",
-      "calc(2em + 3ex)",
-      "calc(50% + 60px)",
-      "calc(-50px)",
-    ],
-    invalid_values: ["20", "-20px"],
-  },
-  "scroll-padding-left": {
-    domProp: "scrollPaddingLeft",
-    inherited: false,
-    type: CSS_TYPE_LONGHAND,
-    initial_values: ["auto"],
-    other_values: [
-      "0",
-      "10px",
-      "20%",
-      "calc(2em + 3ex)",
-      "calc(50% + 60px)",
-      "calc(-50px)",
-    ],
-    invalid_values: ["20", "-20px"],
-  },
-  "scroll-padding-inline": {
-    domProp: "scrollPaddingInline",
-    inherited: false,
-    type: CSS_TYPE_TRUE_SHORTHAND,
-    subproperties: ["scroll-padding-inline-start", "scroll-padding-inline-end"],
-    initial_values: ["auto", "auto auto"],
-    other_values: [
-      "10px",
-      "0",
-      "20%",
-      "calc(2em + 3ex)",
-      "1px 2px",
-      "1px auto",
-    ],
-    invalid_values: ["20", "-20px"],
-  },
-  "scroll-padding-inline-start": {
-    domProp: "scrollPaddingInlineStart",
-    inherited: false,
-    type: CSS_TYPE_LONGHAND,
-    logical: true,
-    initial_values: ["auto"],
-    other_values: [
-      "0",
-      "10px",
-      "20%",
-      "calc(2em + 3ex)",
-      "calc(50% + 60px)",
-      "calc(-50px)",
-    ],
-    invalid_values: ["20", "-20px"],
-  },
-  "scroll-padding-inline-end": {
-    domProp: "scrollPaddingInlineEnd",
-    inherited: false,
-    type: CSS_TYPE_LONGHAND,
-    logical: true,
-    initial_values: ["auto"],
-    other_values: [
-      "0",
-      "10px",
-      "20%",
-      "calc(2em + 3ex)",
-      "calc(50% + 60px)",
-      "calc(-50px)",
-    ],
-    invalid_values: ["20", "-20px"],
-  },
-  "scroll-padding-block": {
-    domProp: "scrollPaddingBlock",
-    inherited: false,
-    type: CSS_TYPE_TRUE_SHORTHAND,
-    subproperties: ["scroll-padding-block-start", "scroll-padding-block-end"],
-    initial_values: ["auto", "auto auto"],
-    other_values: [
-      "10px",
-      "0",
-      "20%",
-      "calc(2em + 3ex)",
-      "1px 2px",
-      "1px auto",
-    ],
-    invalid_values: ["20", "-20px"],
-  },
-  "scroll-padding-block-start": {
-    domProp: "scrollPaddingBlockStart",
-    inherited: false,
-    type: CSS_TYPE_LONGHAND,
-    logical: true,
-    initial_values: ["auto"],
-    other_values: [
-      "0",
-      "10px",
-      "20%",
-      "calc(2em + 3ex)",
-      "calc(50% + 60px)",
-      "calc(-50px)",
-    ],
-    invalid_values: ["20", "-20px"],
-  },
-  "scroll-padding-block-end": {
-    domProp: "scrollPaddingBlockEnd",
-    inherited: false,
-    type: CSS_TYPE_LONGHAND,
-    logical: true,
-    initial_values: ["auto"],
-    other_values: [
-      "0",
-      "10px",
-      "20%",
-      "calc(2em + 3ex)",
-      "calc(50% + 60px)",
-      "calc(-50px)",
-    ],
-    invalid_values: ["20", "-20px"],
-  },
   "table-layout": {
     domProp: "tableLayout",
     inherited: false,
@@ -12423,6 +12093,340 @@ if (IsCSSPropertyPrefEnabled("layout.css.overscroll-behavior.enabled")) {
     invalid_values: ["left", "1px", "contain auto none", "contain nonsense"],
   };
 }
+
+if (IsCSSPropertyPrefEnabled("layout.css.scroll-snap-v1.enabled")) {
+  gCSSProperties["scroll-snap-type"] = {
+    domProp: "scrollSnapType",
+    inherited: false,
+    type: CSS_TYPE_LONGHAND,
+    initial_values: ["none"],
+    other_values: [
+      "both mandatory",
+      "y mandatory",
+      "inline proximity",
+      "both",
+      "x",
+      "y",
+      "block",
+      "inline",
+    ],
+    invalid_values: [
+      "auto",
+      "1px",
+      "x y",
+      "block mandatory inline",
+      "mandatory",
+      "proximity",
+      "mandatory inline",
+      "proximity both",
+      "mandatory x",
+      "proximity y",
+      "mandatory block",
+      "proximity mandatory",
+    ],
+  };
+  gCSSProperties["scroll-snap-align"] = {
+    domProp: "scrollSnapAlign",
+    inherited: false,
+    type: CSS_TYPE_LONGHAND,
+    initial_values: ["none"],
+    other_values: [
+      "start",
+      "end",
+      "center",
+      "start none",
+      "center end",
+      "start start",
+    ],
+    invalid_values: ["auto", "start invalid", "start end center"],
+  };
+  gCSSProperties["scroll-margin"] = {
+    domProp: "scrollMargin",
+    inherited: false,
+    type: CSS_TYPE_TRUE_SHORTHAND,
+    subproperties: [
+      "scroll-margin-top",
+      "scroll-margin-right",
+      "scroll-margin-bottom",
+      "scroll-margin-left",
+    ],
+    initial_values: ["0"],
+    other_values: [
+      "-10px",
+      "calc(2em + 3ex)",
+      "1px 2px",
+      "1px 2px 3px",
+      "1px 2px 3px 4px",
+    ],
+    invalid_values: ["auto", "20%", "-30%", "1px 2px 3px 4px 5px"],
+  };
+  gCSSProperties["scroll-margin-top"] = {
+    domProp: "scrollMarginTop",
+    inherited: false,
+    type: CSS_TYPE_LONGHAND,
+    initial_values: ["0"],
+    other_values: ["-10px", "calc(2em + 3ex)"],
+    invalid_values: ["auto", "20%", "-30%", "1px 2px"],
+  };
+  gCSSProperties["scroll-margin-right"] = {
+    domProp: "scrollMarginRight",
+    inherited: false,
+    type: CSS_TYPE_LONGHAND,
+    initial_values: ["0"],
+    other_values: ["-10px", "calc(2em + 3ex)"],
+    invalid_values: ["auto", "20%", "-30%", "1px 2px"],
+  };
+  gCSSProperties["scroll-margin-bottom"] = {
+    domProp: "scrollMarginBottom",
+    inherited: false,
+    type: CSS_TYPE_LONGHAND,
+    initial_values: ["0"],
+    other_values: ["-10px", "calc(2em + 3ex)"],
+    invalid_values: ["auto", "20%", "-30%", "1px 2px"],
+  };
+  gCSSProperties["scroll-margin-left"] = {
+    domProp: "scrollMarginLeft",
+    inherited: false,
+    type: CSS_TYPE_LONGHAND,
+    initial_values: ["0"],
+    other_values: ["-10px", "calc(2em + 3ex)"],
+    invalid_values: ["auto", "20%", "-30%", "1px 2px"],
+  };
+  gCSSProperties["scroll-margin-inline"] = {
+    domProp: "scrollMarginInline",
+    inherited: false,
+    type: CSS_TYPE_TRUE_SHORTHAND,
+    subproperties: ["scroll-margin-inline-start", "scroll-margin-inline-end"],
+    initial_values: ["0"],
+    other_values: ["-10px", "calc(2em + 3ex)", "1px 2px"],
+    invalid_values: ["auto", "20%", "-30%", "1px 2px 3px"],
+  };
+  gCSSProperties["scroll-margin-inline-start"] = {
+    domProp: "scrollMarginInlineStart",
+    inherited: false,
+    type: CSS_TYPE_LONGHAND,
+    logical: true,
+    initial_values: ["0"],
+    other_values: ["-10px", "calc(2em + 3ex)"],
+    invalid_values: ["auto", "20%", "-30%", "1px 2px"],
+  };
+  gCSSProperties["scroll-margin-inline-end"] = {
+    domProp: "scrollMarginInlineEnd",
+    inherited: false,
+    type: CSS_TYPE_LONGHAND,
+    logical: true,
+    initial_values: ["0"],
+    other_values: ["-10px", "calc(2em + 3ex)"],
+    invalid_values: ["auto", "20%", "-30%", "1px 2px"],
+  };
+  gCSSProperties["scroll-margin-block"] = {
+    domProp: "scrollMarginBlock",
+    inherited: false,
+    type: CSS_TYPE_TRUE_SHORTHAND,
+    subproperties: ["scroll-margin-block-start", "scroll-margin-block-end"],
+    initial_values: ["0"],
+    other_values: ["-10px", "calc(2em + 3ex)", "1px 2px"],
+    invalid_values: ["auto", "20%", "-30%", "1px 2px 3px"],
+  };
+  gCSSProperties["scroll-margin-block-start"] = {
+    domProp: "scrollMarginBlockStart",
+    inherited: false,
+    type: CSS_TYPE_LONGHAND,
+    logical: true,
+    initial_values: ["0"],
+    other_values: ["-10px", "calc(2em + 3ex)"],
+    invalid_values: ["auto", "20%", "-30%", "1px 2px"],
+  };
+  gCSSProperties["scroll-margin-block-end"] = {
+    domProp: "scrollMarginBlockEnd",
+    inherited: false,
+    type: CSS_TYPE_LONGHAND,
+    logical: true,
+    initial_values: ["0"],
+    other_values: ["-10px", "calc(2em + 3ex)"],
+    invalid_values: ["auto", "20%", "-30%", "1px 2px"],
+  };
+  gCSSProperties["scroll-padding"] = {
+    domProp: "scrollPadding",
+    inherited: false,
+    type: CSS_TYPE_TRUE_SHORTHAND,
+    subproperties: [
+      "scroll-padding-top",
+      "scroll-padding-right",
+      "scroll-padding-bottom",
+      "scroll-padding-left",
+    ],
+    initial_values: ["auto"],
+    other_values: [
+      "10px",
+      "0",
+      "20%",
+      "calc(2em + 3ex)",
+      "1px 2px",
+      "1px 2px 3%",
+      "1px 2px 3% 4px",
+      "1px auto",
+    ],
+    invalid_values: ["20", "-20px"],
+  };
+  gCSSProperties["scroll-padding-top"] = {
+    domProp: "scrollPaddingTop",
+    inherited: false,
+    type: CSS_TYPE_LONGHAND,
+    initial_values: ["auto"],
+    other_values: [
+      "0",
+      "10px",
+      "20%",
+      "calc(2em + 3ex)",
+      "calc(50% + 60px)",
+      "calc(-50px)",
+    ],
+    invalid_values: ["20", "-20px"],
+  };
+  gCSSProperties["scroll-padding-right"] = {
+    domProp: "scrollPaddingRight",
+    inherited: false,
+    type: CSS_TYPE_LONGHAND,
+    initial_values: ["auto"],
+    other_values: [
+      "0",
+      "10px",
+      "20%",
+      "calc(2em + 3ex)",
+      "calc(50% + 60px)",
+      "calc(-50px)",
+    ],
+    invalid_values: ["20", "-20px"],
+  };
+  gCSSProperties["scroll-padding-bottom"] = {
+    domProp: "scrollPaddingBottom",
+    inherited: false,
+    type: CSS_TYPE_LONGHAND,
+    initial_values: ["auto"],
+    other_values: [
+      "0",
+      "10px",
+      "20%",
+      "calc(2em + 3ex)",
+      "calc(50% + 60px)",
+      "calc(-50px)",
+    ],
+    invalid_values: ["20", "-20px"],
+  };
+  gCSSProperties["scroll-padding-left"] = {
+    domProp: "scrollPaddingLeft",
+    inherited: false,
+    type: CSS_TYPE_LONGHAND,
+    initial_values: ["auto"],
+    other_values: [
+      "0",
+      "10px",
+      "20%",
+      "calc(2em + 3ex)",
+      "calc(50% + 60px)",
+      "calc(-50px)",
+    ],
+    invalid_values: ["20", "-20px"],
+  };
+  gCSSProperties["scroll-padding-inline"] = {
+    domProp: "scrollPaddingInline",
+    inherited: false,
+    type: CSS_TYPE_TRUE_SHORTHAND,
+    subproperties: ["scroll-padding-inline-start", "scroll-padding-inline-end"],
+    initial_values: ["auto", "auto auto"],
+    other_values: [
+      "10px",
+      "0",
+      "20%",
+      "calc(2em + 3ex)",
+      "1px 2px",
+      "1px auto",
+    ],
+    invalid_values: ["20", "-20px"],
+  };
+  gCSSProperties["scroll-padding-inline-start"] = {
+    domProp: "scrollPaddingInlineStart",
+    inherited: false,
+    type: CSS_TYPE_LONGHAND,
+    logical: true,
+    initial_values: ["auto"],
+    other_values: [
+      "0",
+      "10px",
+      "20%",
+      "calc(2em + 3ex)",
+      "calc(50% + 60px)",
+      "calc(-50px)",
+    ],
+    invalid_values: ["20", "-20px"],
+  };
+  gCSSProperties["scroll-padding-inline-end"] = {
+    domProp: "scrollPaddingInlineEnd",
+    inherited: false,
+    type: CSS_TYPE_LONGHAND,
+    logical: true,
+    initial_values: ["auto"],
+    other_values: [
+      "0",
+      "10px",
+      "20%",
+      "calc(2em + 3ex)",
+      "calc(50% + 60px)",
+      "calc(-50px)",
+    ],
+    invalid_values: ["20", "-20px"],
+  };
+  gCSSProperties["scroll-padding-block"] = {
+    domProp: "scrollPaddingBlock",
+    inherited: false,
+    type: CSS_TYPE_TRUE_SHORTHAND,
+    subproperties: ["scroll-padding-block-start", "scroll-padding-block-end"],
+    initial_values: ["auto", "auto auto"],
+    other_values: [
+      "10px",
+      "0",
+      "20%",
+      "calc(2em + 3ex)",
+      "1px 2px",
+      "1px auto",
+    ],
+    invalid_values: ["20", "-20px"],
+  };
+  gCSSProperties["scroll-padding-block-start"] = {
+    domProp: "scrollPaddingBlockStart",
+    inherited: false,
+    type: CSS_TYPE_LONGHAND,
+    logical: true,
+    initial_values: ["auto"],
+    other_values: [
+      "0",
+      "10px",
+      "20%",
+      "calc(2em + 3ex)",
+      "calc(50% + 60px)",
+      "calc(-50px)",
+    ],
+    invalid_values: ["20", "-20px"],
+  };
+  gCSSProperties["scroll-padding-block-end"] = {
+    domProp: "scrollPaddingBlockEnd",
+    inherited: false,
+    type: CSS_TYPE_LONGHAND,
+    logical: true,
+    initial_values: ["auto"],
+    other_values: [
+      "0",
+      "10px",
+      "20%",
+      "calc(2em + 3ex)",
+      "calc(50% + 60px)",
+      "calc(-50px)",
+    ],
+    invalid_values: ["20", "-20px"],
+  };
+}
+
 if (IsCSSPropertyPrefEnabled("layout.css.webkit-appearance.enabled")) {
   gCSSProperties["-webkit-appearance"] = {
     domProp: "webkitAppearance",

layout/style/test/test_transitions_per_property.html

@@ -324,34 +324,6 @@ var supported_properties = {
                                    test_currentcolor_transition ],
     "text-underline-offset": [ test_length_transition ],
     "text-decoration-thickness": [ test_length_transition ],
-    "scroll-margin-top": [
-      test_length_transition,
-    ],
-    "scroll-margin-right": [
-      test_length_transition,
-    ],
-    "scroll-margin-bottom": [
-      test_length_transition,
-    ],
-    "scroll-margin-left": [
-      test_length_transition,
-    ],
-    "scroll-padding-top": [
-      test_length_transition, test_percent_transition,
-      test_length_clamped, test_percent_clamped,
-    ],
-    "scroll-padding-right": [
-      test_length_transition, test_percent_transition,
-      test_length_clamped, test_percent_clamped,
-    ],
-    "scroll-padding-bottom": [
-      test_length_transition, test_percent_transition,
-      test_length_clamped, test_percent_clamped,
-    ],
-    "scroll-padding-left": [
-      test_length_transition, test_percent_transition,
-      test_length_clamped, test_percent_clamped,
-    ],
 };
 
 if (IsCSSPropertyPrefEnabled("layout.css.motion-path.enabled")) {
@@ -429,6 +401,37 @@ if (IsCSSPropertyPrefEnabled("layout.css.scrollbar-color.enabled")) {
   ];
 }
 
+if (IsCSSPropertyPrefEnabled("layout.css.scroll-snap-v1.enabled")) {
+  supported_properties["scroll-margin-top"] = [
+    test_length_transition,
+  ];
+  supported_properties["scroll-margin-right"] = [
+    test_length_transition,
+  ];
+  supported_properties["scroll-margin-bottom"] = [
+    test_length_transition,
+  ];
+  supported_properties["scroll-margin-left"] = [
+    test_length_transition,
+  ];
+  supported_properties["scroll-padding-top"] = [
+    test_length_transition, test_percent_transition,
+    test_length_clamped, test_percent_clamped,
+  ];
+  supported_properties["scroll-padding-right"] = [
+    test_length_transition, test_percent_transition,
+    test_length_clamped, test_percent_clamped,
+  ];
+  supported_properties["scroll-padding-bottom"] = [
+    test_length_transition, test_percent_transition,
+    test_length_clamped, test_percent_clamped,
+  ];
+  supported_properties["scroll-padding-left"] = [
+    test_length_transition, test_percent_transition,
+    test_length_clamped, test_percent_clamped,
+  ];
+}
+
 // For properties which are well-tested by web-platform-tests, we don't need to
 // test animations/transitions again on them.
 var skipped_transitionable_properties = [
@@ -446,8 +449,10 @@ for (const logical_side of ["inline-start", "inline-end", "block-start", "block-
   supported_properties["margin-" + logical_side] = supported_properties["margin-top"];
   supported_properties["padding-" + logical_side] = supported_properties["padding-top"];
   supported_properties["inset-" + logical_side] = supported_properties["top"];
-  supported_properties["scroll-margin-" + logical_side] = supported_properties["scroll-margin-top"];
-  supported_properties["scroll-padding-" + logical_side] = supported_properties["scroll-padding-top"];
+  if (IsCSSPropertyPrefEnabled("layout.css.scroll-snap-v1.enabled")) {
+    supported_properties["scroll-margin-" + logical_side] = supported_properties["scroll-margin-top"];
+    supported_properties["scroll-padding-" + logical_side] = supported_properties["scroll-padding-top"];
+  }
 }
 
 for (const logical_size of ["inline", "block"]) {

modules/libpref/init/StaticPrefList.yaml

@@ -5240,6 +5240,19 @@
   value: false
   mirror: always
 
+# Is the CSS Scroll Snap Module Level 1 enabled?
+- name: layout.css.scroll-snap-v1.enabled
+  type: RelaxedAtomicBool
+  value: true
+  mirror: always
+
+# Is support for the old unspecced scroll-snap enabled?
+# E.g. scroll-snap-points-{x,y}, scroll-snap-coordinate, etc.
+- name: layout.css.scroll-snap.enabled
+  type: bool
+  value: false
+  mirror: always
+
 # Are shared memory User Agent style sheets enabled?
 - name: layout.css.shared-memory-ua-sheets.enabled
   type: bool

servo/components/style/properties/longhands/box.mako.rs

@@ -454,6 +454,7 @@ ${helpers.predefined_type(
     "ScrollSnapAlign",
     "computed::ScrollSnapAlign::none()",
     engines="gecko",
+    gecko_pref="layout.css.scroll-snap-v1.enabled",
     spec="https://drafts.csswg.org/css-scroll-snap-1/#scroll-snap-align",
     animation_value_type="discrete",
 )}

servo/components/style/properties/longhands/margin.mako.rs

@@ -35,6 +35,7 @@
         "Length",
         "computed::Length::zero()",
         engines="gecko",
+        gecko_pref="layout.css.scroll-snap-v1.enabled",
         logical=side[1],
         logical_group="scroll-margin",
         spec="https://drafts.csswg.org/css-scroll-snap-1/#propdef-scroll-margin-%s" % side[0],

servo/components/style/properties/longhands/padding.mako.rs

@@ -34,6 +34,7 @@
         "NonNegativeLengthPercentageOrAuto",
         "computed::NonNegativeLengthPercentageOrAuto::auto()",
         engines="gecko",
+        gecko_pref="layout.css.scroll-snap-v1.enabled",
         logical=side[1],
         logical_group="scroll-padding",
         spec="https://drafts.csswg.org/css-scroll-snap-1/#propdef-scroll-padding-%s" % side[0],

servo/components/style/properties/shorthands/margin.mako.rs

@@ -38,6 +38,7 @@ ${helpers.four_sides_shorthand(
     "specified::Length::parse",
     engines="gecko",
     spec="https://drafts.csswg.org/css-scroll-snap-1/#propdef-scroll-margin",
+    gecko_pref="layout.css.scroll-snap-v1.enabled",
 )}
 
 ${helpers.two_properties_shorthand(
@@ -47,6 +48,7 @@ ${helpers.two_properties_shorthand(
     "specified::Length::parse",
     engines="gecko",
     spec="https://drafts.csswg.org/css-scroll-snap-1/#propdef-scroll-margin-block",
+    gecko_pref="layout.css.scroll-snap-v1.enabled",
 )}
 
 ${helpers.two_properties_shorthand(
@@ -56,4 +58,5 @@ ${helpers.two_properties_shorthand(
     "specified::Length::parse",
     engines="gecko",
     spec="https://drafts.csswg.org/css-scroll-snap-1/#propdef-scroll-margin-inline",
+    gecko_pref="layout.css.scroll-snap-v1.enabled",
 )}

servo/components/style/properties/shorthands/padding.mako.rs

@@ -36,6 +36,7 @@ ${helpers.four_sides_shorthand(
     "scroll-padding-%s",
     "specified::NonNegativeLengthPercentageOrAuto::parse",
     engines="gecko",
+    gecko_pref="layout.css.scroll-snap-v1.enabled",
     spec="https://drafts.csswg.org/css-scroll-snap-1/#propdef-scroll-padding"
 )}
 
@@ -45,6 +46,7 @@ ${helpers.two_properties_shorthand(
     "scroll-padding-block-end",
     "specified::NonNegativeLengthPercentageOrAuto::parse",
     engines="gecko",
+    gecko_pref="layout.css.scroll-snap-v1.enabled",
     spec="https://drafts.csswg.org/css-scroll-snap-1/#propdef-scroll-padding-block"
 )}
 
@@ -54,6 +56,7 @@ ${helpers.two_properties_shorthand(
     "scroll-padding-inline-end",
     "specified::NonNegativeLengthPercentageOrAuto::parse",
     engines="gecko",
+    gecko_pref="layout.css.scroll-snap-v1.enabled",
     spec="https://drafts.csswg.org/css-scroll-snap-1/#propdef-scroll-padding-inline"
 )}
 

testing/web-platform/meta/css/css-scroll-snap/__dir__.ini

@@ -0,0 +1 @@
+prefs: [layout.css.scroll-snap-v1.enabled:true]

testing/web-platform/meta/css/cssom-view/__dir__.ini

@@ -0,0 +1 @@
+prefs: [layout.css.scroll-snap-v1.enabled:true]