Bug 2003593 - Invalidate for anchor changes correctly. r=dshin,layout-anchor-positioning-reviewers,firefox-style-system-reviewers,layout-reviewers

We need to start the reflow from our parent, even if we happen to be a
reflow root.

Differential Revision: https://phabricator.services.mozilla.com/D274805

Author: emilio

layout/base/AnchorPositioningUtils.cpp

@@ -951,8 +951,7 @@ static bool TriggerFallbackReflow(PresShell* aPresShell, nsIFrame* aPositioned,
   // We want to retry from the first position; remove the last position
   // property so all potential positions are re-evaluated.
   aPositioned->RemoveProperty(nsIFrame::LastSuccessfulPositionFallback());
-  aPresShell->FrameNeedsReflow(aPositioned, mozilla::IntrinsicDirty::None,
-                               NS_FRAME_IS_DIRTY);
+  aPresShell->MarkPositionedFrameForReflow(aPositioned);
   return true;
 }
 

layout/base/PresShell.cpp

@@ -11575,9 +11575,7 @@ PresShell::AnchorPosUpdateResult PresShell::UpdateAnchorPosLayout() {
     }
     if (shouldReflow) {
       result = AnchorPosUpdateResult::NeedReflow;
-      // Abspos frames should not affect ancestor intrinsics.
-      FrameNeedsReflow(positioned, IntrinsicDirty::None,
-                       NS_FRAME_HAS_DIRTY_CHILDREN);
+      MarkPositionedFrameForReflow(positioned);
     }
   }
   return result;
@@ -11817,8 +11815,7 @@ void PresShell::UpdateAnchorPosForScroll(
           accService->NotifyAnchorPositionedScrollUpdate(this, positioned);
         }
 #endif
-        FrameNeedsReflow(positioned, IntrinsicDirty::None,
-                         NS_FRAME_HAS_DIRTY_CHILDREN);
+        MarkPositionedFrameForReflow(positioned);
       }
     }
   }
@@ -12146,13 +12143,19 @@ size_t PresShell::SizeOfTextRuns(MallocSizeOf aMallocSizeOf) const {
                                                 /* clear = */ false);
 }
 
-void PresShell::MarkFixedFramesForReflow(IntrinsicDirty aIntrinsicDirty) {
+void PresShell::MarkPositionedFrameForReflow(nsIFrame* aFrame) {
+  // Abspos frames don't affect intrinsic sizes of ancestors.
+  FrameNeedsReflow(aFrame, IntrinsicDirty::None, NS_FRAME_HAS_DIRTY_CHILDREN,
+                   ReflowRootHandling::PositionOrSizeChange);
+}
+
+void PresShell::MarkFixedFramesForReflow() {
   nsIFrame* rootFrame = mFrameConstructor->GetRootFrame();
   if (rootFrame) {
     const nsFrameList& childList =
         rootFrame->GetChildList(FrameChildListID::Fixed);
     for (nsIFrame* childFrame : childList) {
-      FrameNeedsReflow(childFrame, aIntrinsicDirty, NS_FRAME_IS_DIRTY);
+      MarkPositionedFrameForReflow(childFrame);
     }
   }
 }
@@ -12230,7 +12233,7 @@ void PresShell::CompleteChangeToVisualViewportSize() {
     if (ScrollContainerFrame* sf = GetRootScrollContainerFrame()) {
       sf->MarkScrollbarsDirtyForReflow();
     }
-    MarkFixedFramesForReflow(IntrinsicDirty::None);
+    MarkFixedFramesForReflow();
   }
 
   MaybeReflowForInflationScreenSizeChange();

layout/base/PresShell.h

@@ -1544,7 +1544,10 @@ class PresShell final : public nsStubDocumentObserver,
   /**
    * Calls FrameNeedsReflow on all fixed position children of the root frame.
    */
-  void MarkFixedFramesForReflow(IntrinsicDirty aIntrinsicDirty);
+  void MarkFixedFramesForReflow();
+  // Marks a positioned frame for reflow, assuming that size or position of the
+  // frame might change.
+  void MarkPositionedFrameForReflow(nsIFrame*);
 
   /**
    * Similar to above MarkFixedFramesForReflow, but for sticky position children

layout/base/nsPresContext.cpp

@@ -2948,7 +2948,7 @@ void nsPresContext::UpdateDynamicToolbarOffset(ScreenIntCoord aOffset) {
   // position:fixed or position:sticky element is painted at the correct
   // position on the main-thread.
   if (mDynamicToolbarHeight == 0 || aOffset == -mDynamicToolbarMaxHeight) {
-    mPresShell->MarkFixedFramesForReflow(IntrinsicDirty::None);
+    mPresShell->MarkFixedFramesForReflow();
     mPresShell->MarkStickyFramesForReflow();
     mPresShell->ScheduleResizeEventIfNeeded(
         PresShell::ResizeEventKind::Regular);

layout/style/nsStyleStruct.cpp

@@ -1257,7 +1257,7 @@ nsChangeHint nsStylePosition::CalcDifference(
       mPositionArea != aNewData.mPositionArea) {
     // We need to reflow in order to update the `AnchorPosReferences`
     // property at minimum.
-    hint |= nsChangeHint_NeedReflow;
+    hint |= nsChangeHint_NeedReflow | nsChangeHint_ReflowChangesSizeOrPosition;
   }
 
   if (mAspectRatio != aNewData.mAspectRatio) {

testing/web-platform/tests/css/css-anchor-position/anchor-name-dynamic-reflow-root-ref.html

@@ -0,0 +1,14 @@
+<!DOCTYPE html>
+<meta charset="utf-8">
+<style>
+body { margin: 0 }
+.green {
+  position: absolute;
+  top: 20px;
+  left: 100px;
+  width: 100px;
+  height: 100px;
+  background-color: green;
+}
+</style>
+<div class="green"></div>

testing/web-platform/tests/css/css-anchor-position/anchor-name-dynamic-reflow-root.html

@@ -0,0 +1,45 @@
+<!DOCTYPE html>
+<html class="reftest-wait">
+<meta charset="utf-8">
+<title>Dynamic changes to anchor-name and reflow roots</title>
+<link rel="help" href="https://drafts.csswg.org/css-anchor-position-1/#anchor-name">
+<link rel="help" href="https://bugzilla.mozilla.org/show_bug.cgi?id=2003593">
+<link rel="author" title="Emilio Cobos Álvarez" href="mailto:emilio@crisal.io">
+<link rel="author" title="Mozilla" href="https://mozilla.com">
+<link rel="match" href="anchor-name-dynamic-reflow-root-ref.html">
+<style>
+body { margin: 0 }
+.tabs {
+  display: flex;
+}
+.tab {
+  height: 20px;
+  width: 100px;
+}
+.cur {
+  anchor-name: --current-tab;
+}
+.highlight {
+  position: absolute;
+  width: anchor-size(width);
+  left: anchor(left);
+  right: anchor(right);
+  height: 100px;
+  background: green;
+  top: anchor(bottom);
+  position-anchor: --current-tab;
+  transform: scaleY(1); /* This is important to test the bug */
+}
+</style>
+<div class=tabs>
+  <div id=t1 class="tab cur"></div>
+  <div id=t2 class="tab"></div>
+  <div class=highlight></div>
+</div>
+<script>
+document.addEventListener("TestRendered", function() {
+  t1.classList.remove('cur');
+  t2.classList.add('cur');
+  document.documentElement.className = "";
+});
+</script>