Bug 1990094 - Notify a11y cache of details relation changes caused by scroll. r=Jamie,jwatt

Differential Revision: https://phabricator.services.mozilla.com/D270902

Author: eeejay

accessible/base/nsAccessibilityService.cpp

@@ -715,6 +715,26 @@ void nsAccessibilityService::NotifyAnchorRemoved(mozilla::PresShell* aPresShell,
   }
 }
 
+void nsAccessibilityService::NotifyAnchorPositionedScrollUpdate(
+    mozilla::PresShell* aPresShell, nsIFrame* aFrame) {
+  DocAccessible* document = aPresShell->GetDocAccessible();
+  if (!document) {
+    return;
+  }
+
+  if (LocalAccessible* positionedAcc =
+          document->GetAccessible(aFrame->GetContent())) {
+    // Refresh relations before reflow to notify current anchor.
+    document->RefreshAnchorRelationCacheForTarget(positionedAcc);
+
+    // Refresh relations after next tick when reflow updated to the
+    // new anchor state.
+    document->Controller()->ScheduleNotification<DocAccessible>(
+        document, &DocAccessible::RefreshAnchorRelationCacheForTarget,
+        positionedAcc);
+  }
+}
+
 void nsAccessibilityService::NotifyAttrElementWillChange(
     mozilla::dom::Element* aElement, nsAtom* aAttr) {
   mozilla::dom::Document* doc = aElement->OwnerDoc();

accessible/base/nsAccessibilityService.h

@@ -283,6 +283,14 @@ class nsAccessibilityService final : public mozilla::a11y::DocManager,
    */
   void NotifyAnchorRemoved(mozilla::PresShell* aPresShell, nsIFrame* aFrame);
 
+  /**
+   * Notify accessibility that an anchor positioned frame has
+   * been marked for reflow because of a scroll change for one of its
+   * anchors. A fallback anchor may be activated or deactivated.
+   */
+  void NotifyAnchorPositionedScrollUpdate(mozilla::PresShell* aPresShell,
+                                          nsIFrame* aFrame);
+
   /**
    * Notify accessibility that an element explicitly set for an attribute is
    * about to change. See dom::Element::ExplicitlySetAttrElement.

accessible/tests/browser/relations/browser_anchor_positioning.js

@@ -663,3 +663,80 @@ addAccessibleTask(
   },
   { chrome: true, topLevel: true }
 );
+
+addAccessibleTask(
+  `
+<style>
+.anchor {
+  width: 50px;
+  height: 50px;
+  background: pink;
+}
+
+.positioned {
+  width: 50px;
+  height: 50px;
+  background: purple;
+  position: absolute;
+  position-anchor: --a;
+  left: anchor(right);
+  bottom: anchor(bottom);
+  position-try-fallbacks: --fb;
+}
+
+@position-try --fb {
+  position-anchor: --b;
+}
+
+.abs-cb {
+  width: 200px;
+  height: 200px;
+  border: 1px solid;
+  position: relative;
+}
+
+.scroller {
+  overflow: scroll;
+  width: 100%;
+  height: 100%;
+  border: 1px solid;
+  box-sizing: border-box;
+}
+
+.filler {
+  height: 125px;
+  width: 1px;
+}
+
+.dn {
+  display: none;
+}
+</style>
+<div class="abs-cb">
+  <div class="scroller">
+    <div class="filler"></div>
+    <div class="anchor" id="anchor1" style="anchor-name: --a;" role="group"></div>
+    <div class="filler"></div>
+    <div class="anchor" id="anchor2" style="anchor-name: --b; background: aqua;" role="group"></div>
+    <div class="filler"></div>
+  </div>
+  <div id="target" class="positioned" role="group"></div>
+</div>`,
+  async function testScrollWithFallback(browser, docAcc) {
+    const anchor1 = findAccessibleChildByID(docAcc, "anchor1");
+    const anchor2 = findAccessibleChildByID(docAcc, "anchor2");
+    const target = findAccessibleChildByID(docAcc, "target");
+
+    info("Correct details relation before scroll");
+    await testDetailsRelations(anchor1, target);
+
+    await invokeContentTaskAndTick(browser, [], () => {
+      let scroller = content.document.querySelector(".scroller");
+      scroller.scrollTo(0, scroller.scrollTopMax);
+    });
+
+    info("Correct details relation after scroll");
+    await testDetailsRelations(anchor2, target);
+  },
+  { chrome: true, topLevel: true }
+);

layout/base/PresShell.cpp

@@ -11967,6 +11967,11 @@ void PresShell::UpdateAnchorPosForScroll(
       positioned->GetParent()->UpdateOverflow();
       referenceData.mDefaultScrollShift = offset;
       if (CheckOverflow(positioned, offset, referenceData)) {
+#ifdef ACCESSIBILITY
+        if (nsAccessibilityService* accService = GetAccService()) {
+          accService->NotifyAnchorPositionedScrollUpdate(this, positioned);
+        }
+#endif
         FrameNeedsReflow(positioned, IntrinsicDirty::None,
                          NS_FRAME_HAS_DIRTY_CHILDREN);
       }