Skip returning the snap target if the scroll-snap-type on the axis is `none`.
If we return the snap target in such cases, even though the target position is
unchanged from the original scroll destination, the target will be handled as a
valid last-snapped target element, thus we will try to re-snap to the element's
scroll-snap-align position rather than keeping the scroll position as it is.
Differential Revision: https://phabricator.services.mozilla.com/D152353
bugzilla-url: https://bugzilla.mozilla.org/show_bug.cgi?id=1780154
gecko-commit: 68caee424b216d4241d3635748b288723952781e
gecko-reviewers: botond
diff --git a/css/css-scroll-snap/snap-after-relayout/not-resnap-outside-proximity-threshold.html b/css/css-scroll-snap/snap-after-relayout/not-resnap-outside-proximity-threshold.html
new file mode 100644
index 0000000..b2c5720
--- /dev/null
+++ b/css/css-scroll-snap/snap-after-relayout/not-resnap-outside-proximity-threshold.html
@@ -0,0 +1,66 @@
+<!DOCTYPE html>
+<title>
+ Not re-snap once after a scroll operation has finished without snapping
+ because the scroll destination was outside of the snap proximity threshold.
+</title>
+<!-- This test assumes that all major browsers' default scroll-snap proximity
+ thresholds are greater than 200px. -->
+<link rel="help" href="https://drafts.csswg.org/css-scroll-snap/#re-snap" />
+<link rel="help" href="https://bugzilla.mozilla.org/show_bug.cgi?id=1780154">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<style>
+div {
+ position: absolute;
+ margin: 0;
+}
+
+#scroller {
+ height: 600px;
+ width: 600px;
+ overflow: hidden;
+ scroll-snap-type: y proximity;
+}
+
+.snap {
+ width: 300px;
+ height: 300px;
+ background-color: green;
+ scroll-snap-align: start;
+}
+
+.area {
+ width: 2000px;
+ height: 2000px;
+}
+</style>
+
+<div id="scroller">
+ <div class="area"></div>
+ <div class="snap" style="top: 0px;"></div>
+ <div class="snap" style="top: 500px;"></div>
+</div>
+
+<script>
+test(() => {
+ // The initial snap position is at (0, 0).
+ assert_equals(scroller.scrollTop, 0);
+ assert_equals(scroller.scrollLeft, 0);
+
+ // Scroll to a position where it's outside of the scroll-snap proximity
+ // threshold, so that it won't trigger snapping.
+ scroller.scrollTo(0, 250);
+
+ assert_equals(scroller.scrollTop, 250);
+ assert_equals(scroller.scrollLeft, 0);
+
+ // Changing the initial snap target position, but still it's outside of the
+ // threshold.
+ document.querySelectorAll(".snap")[0].style.top = "10px";
+
+ // Not re-snap to the last snap point.
+ assert_equals(scroller.scrollTop, 250);
+ assert_equals(scroller.scrollLeft, 0);
+}, "Not re-snap once after a scroll operation has finished without snapping " +
+ "because the scroll destination was outside of the snap proximity threshold.");
+</script>
