Bug 1367568 part 4: Add mochitest to ensure we don't reflow too much for "overflow" changes on <body>. r?bz
MozReview-Commit-ID: KD0nv0ckKu
--- a/layout/style/test/mochitest.ini
+++ b/layout/style/test/mochitest.ini
@@ -307,16 +307,17 @@ skip-if = toolkit == 'android' # bug 775
[test_value_computation.html]
skip-if = toolkit == 'android'
[test_value_storage.html]
[test_variable_serialization_computed.html]
[test_variable_serialization_specified.html]
[test_variables.html]
support-files = support/external-variable-url.css
[test_video_object_fit.html]
+[test_viewport_scrollbar_causing_reflow.html]
[test_viewport_units.html]
[test_visited_image_loading.html]
skip-if = (toolkit == 'android' || stylo) # TIMED_OUT for android, timeout bug 1328511 for stylo
[test_visited_image_loading_empty.html]
skip-if = (toolkit == 'android' || stylo) # TIMED_OUT for android, timeout bug 1328511 for stylo
[test_visited_lying.html]
skip-if = (toolkit == 'android' || stylo) # TIMED_OUT for android, timeout bug 1328511 for stylo
[test_visited_pref.html]
new file mode 100644
--- /dev/null
+++ b/layout/style/test/test_viewport_scrollbar_causing_reflow.html
@@ -0,0 +1,125 @@
+<!DOCTYPE HTML>
+<html>
+<!--
+https://bugzilla.mozilla.org/show_bug.cgi?id=1367568
+-->
+<head>
+ <meta charset="utf-8">
+ <title>Test for Bug 1367568</title>
+ <script type="application/javascript" src="/tests/SimpleTest/SimpleTest.js"></script>
+ <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
+</head>
+<body>
+<a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=">Mozilla Bug 1367568</a>
+<div id="content">
+ <!-- Some fixed-width divs that we shouldn't have to reflow when the viewport
+ changes: -->
+ <div style="width: 100px">
+ fixed-width
+ <div>(child)</div>
+ </div>
+ <div style="position: absolute; width: 150px">
+ abs-fixed-width
+ <div>(child)</div>
+ </div>
+</div>
+<pre id="test">
+<script type="application/javascript">
+"use strict";
+
+/** Test for Bug 1367568 **/
+
+/**
+ * This test verifies that "overflow" changes on the <body> don't cause
+ * an unnecessarily large amount of reflow.
+ */
+
+// Vars used in setStyleAndMeasure that we really only have to look up once:
+const gUtils = SpecialPowers.getDOMWindowUtils(window);
+
+function setStyleAndMeasure(initialStyle, finalStyle) {
+ is(document.body.style.length, 0,
+ "Bug in test - body should start with empty style");
+ let unusedVal = document.body.offsetHeight; // flush layout
+ let constructCount = gUtils.framesConstructed;
+
+ document.body.style = initialStyle;
+ unusedVal = document.body.offsetHeight; // flush layout
+ let reflowCountBeforeTweak = gUtils.framesReflowed;
+
+ document.body.style = finalStyle;
+ unusedVal = document.body.offsetHeight; // flush layout
+ let reflowCountAfterTweak = gUtils.framesReflowed;
+
+ // Clean up:
+ document.body.style = "";
+
+ is(gUtils.framesConstructed, constructCount,
+ "Style tweak shouldn't have triggered frame construction");
+
+ // ...and return the delta:
+ return reflowCountAfterTweak - reflowCountBeforeTweak;
+}
+
+function main() {
+ // First, we sanity-check that our measurement make sense -- if we leave
+ // styles unchanged, we should measure no frames being reflowed:
+ let count = setStyleAndMeasure("width: 50px; height: 80px",
+ "width: 50px; height: 80px");
+ is(count, 0,
+ "Shouldn't reflow anything when we leave 'width' & 'height' unchanged");
+
+ // Now: see how many frames are reflowed when the "width" & "height" change.
+ // We'll use this as the reference when measuring reflow counts for various
+ // changes to "overflow" below.
+ count = setStyleAndMeasure("width: 50px; height: 80px",
+ "width: 90px; height: 60px");
+ ok(count > 0,
+ "Should reflow some frames when 'width' & 'height' change");
+
+ // Expected maximum number of frames reflowed for "overflow" changes
+ // (+2 is to allow for reflowing scrollbars themselves):
+ const expectedMax = count + 2;
+
+ // Shared ending for messages in all ok() checks below:
+ const messageSuffix =
+ " shouldn't be greater than count for tweaking width/height on body (" +
+ expectedMax + ")";
+
+ // OK, here is where the relevant tests actually begin!!
+ // See how many frames we reflow for various tweaks to "overflow" on
+ // the body -- we expect the count to be no larger than |expectedMax|.
+ count = setStyleAndMeasure("", "overflow: scroll");
+ ok(count <= expectedMax,
+ "Reflow count when setting 'overflow: scroll' on body (" + count + ")" +
+ messageSuffix);
+
+ count = setStyleAndMeasure("", "overflow: hidden");
+ ok(count <= expectedMax,
+ "Reflow count when setting 'overflow: hidden' on body (" + count + ")" +
+ messageSuffix);
+
+ // Test removal of "overflow: scroll":
+ count = setStyleAndMeasure("overflow: scroll", "");
+ ok(count <= expectedMax,
+ "Reflow count when removing 'overflow: scroll' from body (" + count + ")" +
+ messageSuffix);
+
+ count = setStyleAndMeasure("overflow: hidden", "");
+ ok(count <= expectedMax,
+ "Reflow count when removing 'overflow: hidden' from body (" + count + ")" +
+ messageSuffix);
+
+ // Test change between two non-'visible' overflow values:
+ count = setStyleAndMeasure("overflow: scroll", "overflow: hidden");
+ ok(count <= expectedMax,
+ "Reflow count when changing 'overflow' on body (" + count + ")" +
+ messageSuffix);
+}
+
+main();
+
+</script>
+</pre>
+</body>
+</html>