Properly distinguish between empty children and no children in rule iterator.
So that skip_children(), which just pops the stack and is used by the
dynamic media query evaluation code, works as it should.
Differential Revision: https://phabricator.services.mozilla.com/D92717
bugzilla-url: https://bugzilla.mozilla.org/show_bug.cgi?id=1669600
gecko-commit: e6b1234900b328782dd4f93b34222bf49b470ac2
gecko-reviewers: heycam
diff --git a/css/mediaqueries/mq-dynamic-empty-children.html b/css/mediaqueries/mq-dynamic-empty-children.html
new file mode 100644
index 0000000..3edda87
--- /dev/null
+++ b/css/mediaqueries/mq-dynamic-empty-children.html
@@ -0,0 +1,40 @@
+<!doctype html>
+<title>Dynamic evaluation of media queries works fine in presence of empty media rule</title>
+<link rel="author" href="mailto:emilio@crisal.io" title="Emilio Cobos Álvarez">
+<link rel="author" href="https://mozilla.org" title="Mozilla">
+<link rel="help" href="https://bugzilla.mozilla.org/show_bug.cgi?id=1669600">
+<link rel="help" href="https://drafts.csswg.org/mediaqueries-4/">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<iframe width=500 height=300 frameborder=0></iframe>
+<script>
+let iframe = document.querySelector("iframe");
+promise_test(async function (t) {
+ await new Promise(resolve => {
+ window.addEventListener("load", resolve);
+ });
+ let frameLoaded = new Promise(resolve => {
+ iframe.addEventListener("load", resolve);
+ });
+ iframe.srcdoc = `
+ <style>
+ :root { background-color: red; }
+ /* This one should never apply */
+ @media (min-width: 1500px) {}
+ /* This one should change and start matching */
+ @media (max-width: 400px) {
+ :root { background-color: lime; }
+ }
+ </style>
+ `;
+ await frameLoaded;
+
+ function getColor() {
+ return iframe.contentWindow.getComputedStyle(iframe.contentDocument.documentElement).backgroundColor;
+ }
+
+ assert_equals(getColor(), "rgb(255, 0, 0)", "Should start red");
+ iframe.width = 400;
+ assert_equals(getColor(), "rgb(0, 255, 0)", "Should turn green");
+});
+</script>
