gecko-dev/browser/base/content/test/performance/browser_tabswitch.js

/* Any copyright is dedicated to the Public Domain.
   http://creativecommons.org/publicdomain/zero/1.0/ */

"use strict";

/**
 * WHOA THERE: We should never be adding new things to EXPECTED_REFLOWS. This
 * is a whitelist that should slowly go away as we improve the performance of
 * the front-end. Instead of adding more reflows to the whitelist, you should
 * be modifying your code to avoid the reflow.
 *
 * See https://developer.mozilla.org/en-US/Firefox/Performance_best_practices_for_Firefox_fe_engineers
 * for tips on how to do that.
 */
const EXPECTED_REFLOWS = [
  /**
   * Nothing here! Please don't add anything new!
   */
];

/*
 * This test ensures that there are no unexpected
 * uninterruptible reflows when switching between two
 * tabs that are both fully visible.
 */
add_task(async function() {
  await ensureNoPreloadedBrowser();

  // At the time of writing, there are no reflows on simple tab switching.
  // Mochitest will fail if we have no assertions, so we add one here
  // to make sure nobody adds any new ones.
  Assert.equal(
    EXPECTED_REFLOWS.length,
    0,
    "We shouldn't have added any new expected reflows."
  );

  let origTab = gBrowser.selectedTab;
  let firstSwitchDone = BrowserTestUtils.waitForEvent(window, "TabSwitchDone");
  let otherTab = await BrowserTestUtils.openNewForegroundTab(gBrowser);
  await firstSwitchDone;

  let tabStripRect = gBrowser.tabContainer.arrowScrollbox.getBoundingClientRect();
  let firstTabRect = origTab.getBoundingClientRect();
  let inRange = (val, min, max) => min <= val && val <= max;

  await withPerfObserver(
    async function() {
      let switchDone = BrowserTestUtils.waitForEvent(window, "TabSwitchDone");
      gBrowser.selectedTab = origTab;
      await switchDone;
    },
    {
      expectedReflows: EXPECTED_REFLOWS,
      frames: {
        filter: rects =>
          rects.filter(
            r =>
              !// We expect all changes to be within the tab strip.
              (
                r.y1 >= tabStripRect.top &&
                r.y2 <= tabStripRect.bottom &&
                r.x1 >= tabStripRect.left &&
                r.x2 <= tabStripRect.right &&
                // The tab selection changes between 2 adjacent tabs, so we expect
                // both to change color at once: this should be a single rect of the
                // width of 2 tabs.
                inRange(
                  r.w,
                  (origTab.clientWidth - 1) * 2, // -1 for the border on Win7
                  origTab.clientWidth * 2
                )
              )
          ),
        exceptions: [
          {
            name:
              "bug 1446454 - the border between tabs should be painted at" +
              " the same time as the tab switch",
            condition: r =>
              // In tab strip
              r.y1 >= tabStripRect.top &&
              r.y2 <= tabStripRect.bottom &&
              // 1px border, 1px before the end of the first tab.
              r.w == 1 &&
              r.x1 == firstTabRect.right - 1,
          },
          {
            name: "bug 1446449 - spurious tab switch spinner",
            condition: r =>
              AppConstants.DEBUG &&
              // In the content area
              r.y1 >=
                document.getElementById("appcontent").getBoundingClientRect()
                  .top,
          },
        ],
      },
    }
  );

  BrowserTestUtils.removeTab(otherTab);
});