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rustdoc: optimize loading of source sidebar

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The source sidebar has a setting to remember whether it should be open or
closed. Previously, this setting was handled in source-script.js, which
is loaded with `defer`, meaning it is often run after the document is rendered.
Since CSS renders the source sidebar as closed by default, changing this
after the initial render results in a relayout.

Instead, handle the setting in storage.js, which is the first script to load
and is the only script that blocks render. This avoids a relayout and means
navigating between files with the sidebar open is faster.
This commit is contained in:
Jacob Hoffman-Andrews 2022-06-20 12:41:11 -07:00
parent bb8c2f4117
commit b37a05bd01
5 changed files with 42 additions and 26 deletions
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11
src/librustdoc/html/static/js/storage.js
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@ -1,3 +1,8 @@
// storage.js is loaded in the `<head>` of all rustdoc pages and doesn't
// use `async` or `defer`. That means it blocks further parsing and rendering
// of the page: https://developer.mozilla.org/en-US/docs/Web/HTML/Element/script.
// This makes it the correct place to act on settings that affect the display of
// the page, so we don't see major layout changes during the load of the page.
"use strict";
const darkThemes = ["dark", "ayu"];
@ -236,6 +241,12 @@ if (getSettingValue("use-system-theme") !== "false" && window.matchMedia) {
switchToSavedTheme();
}
if (getSettingValue("source-sidebar-show") === "true") {
// At this point in page load, `document.body` is not available yet.
// Set a class on the `<html>` element instead.
addClass(document.documentElement, "source-sidebar-expanded");
}
// If we navigate away (for example to a settings page), and then use the back or
// forward button to get back to a page, the theme may have changed in the meantime.
// But scripts may not be re-loaded in such a case due to the bfcache