From 6b60bc64087e130f30e3bc095a3ef9e0c1790fef Mon Sep 17 00:00:00 2001
From: Michael Howell <michael@notriddle.com>
Date: Thu, 30 Jun 2022 17:28:29 -0700
Subject: rustdoc: improve scroll locking in the rustdoc mobile sidebars

This commit ports the scroll locking behavior from the source sidebar to the
regular sidebar, and also fixes some bad behavior where opening a "mobile"
sidebar, and growing the viewport so that the "desktop" mode without scroll
locking is activated, could potentially leave the page stuck.

This does not affect the behavior on larger screens. Only small ones, where
the sidebar covers up the main content.
---
 src/librustdoc/html/static/js/main.js          | 46 +++++++++++++++++++++++---
 src/librustdoc/html/static/js/source-script.js | 20 +++++++++--
 2 files changed, 59 insertions(+), 7 deletions(-)

(limited to 'src/librustdoc/html')

diff --git a/src/librustdoc/html/static/js/main.js b/src/librustdoc/html/static/js/main.js
index 6658f07ce01..045dfe313df 100644
--- a/src/librustdoc/html/static/js/main.js
+++ b/src/librustdoc/html/static/js/main.js
@@ -348,8 +348,7 @@ function loadCss(cssFileName) {
 
     function onHashChange(ev) {
         // If we're in mobile mode, we should hide the sidebar in any case.
-        const sidebar = document.getElementsByClassName("sidebar")[0];
-        removeClass(sidebar, "shown");
+        hideSidebar();
         handleHashes(ev);
     }
 
@@ -731,11 +730,50 @@ function loadCss(cssFileName) {
         });
     }());
 
+    let oldSidebarScrollPosition = null;
+
+    function showSidebar() {
+        if (window.innerWidth < window.RUSTDOC_MOBILE_BREAKPOINT) {
+            // This is to keep the scroll position on mobile.
+            oldSidebarScrollPosition = window.scrollY;
+            document.body.style.width = `${document.body.offsetWidth}px`;
+            document.body.style.position = "fixed";
+            document.body.style.top = `-${oldSidebarScrollPosition}px`;
+            document.querySelector(".mobile-topbar").style.top = `${oldSidebarScrollPosition}px`;
+            document.querySelector(".mobile-topbar").style.position = "relative";
+        } else {
+            oldSidebarScrollPosition = null;
+        }
+        const sidebar = document.getElementsByClassName("sidebar")[0];
+        addClass(sidebar, "shown");
+    }
+
     function hideSidebar() {
+        if (oldSidebarScrollPosition !== null) {
+            // This is to keep the scroll position on mobile.
+            document.body.style.width = "";
+            document.body.style.position = "";
+            document.body.style.top = "";
+            document.querySelector(".mobile-topbar").style.top = "";
+            document.querySelector(".mobile-topbar").style.position = "";
+            // The scroll position is lost when resetting the style, hence why we store it in
+            // `oldSidebarScrollPosition`.
+            window.scrollTo(0, oldSidebarScrollPosition);
+            oldSidebarScrollPosition = null;
+        }
         const sidebar = document.getElementsByClassName("sidebar")[0];
         removeClass(sidebar, "shown");
     }
 
+    window.addEventListener("resize", () => {
+        if (window.innerWidth >= window.RUSTDOC_MOBILE_BREAKPOINT &&
+            oldSidebarScrollPosition !== null) {
+            // If the user opens the sidebar in "mobile" mode, and then grows the browser window,
+            // we need to switch away from mobile mode and make the main content area scrollable.
+            hideSidebar();
+        }
+    });
+
     function handleClick(id, f) {
         const elem = document.getElementById(id);
         if (elem) {
@@ -778,9 +816,9 @@ function loadCss(cssFileName) {
         sidebar_menu_toggle.addEventListener("click", () => {
             const sidebar = document.getElementsByClassName("sidebar")[0];
             if (!hasClass(sidebar, "shown")) {
-                addClass(sidebar, "shown");
+                showSidebar();
             } else {
-                removeClass(sidebar, "shown");
+                hideSidebar();
             }
         });
     }
diff --git a/src/librustdoc/html/static/js/source-script.js b/src/librustdoc/html/static/js/source-script.js
index 1e9bfa5cc89..c5bfc00c78b 100644
--- a/src/librustdoc/html/static/js/source-script.js
+++ b/src/librustdoc/html/static/js/source-script.js
@@ -10,7 +10,7 @@
 (function() {
 
 const rootPath = document.getElementById("rustdoc-vars").attributes["data-root-path"].value;
-let oldScrollPosition = 0;
+let oldScrollPosition = null;
 
 function closeSidebarIfMobile() {
     if (window.innerWidth < window.RUSTDOC_MOBILE_BREAKPOINT) {
@@ -71,18 +71,21 @@ function toggleSidebar() {
             oldScrollPosition = window.scrollY;
             document.body.style.position = "fixed";
             document.body.style.top = `-${oldScrollPosition}px`;
+        } else {
+            oldScrollPosition = null;
         }
         addClass(document.documentElement, "source-sidebar-expanded");
         child.innerText = "<";
         updateLocalStorage("source-sidebar-show", "true");
     } else {
-        if (window.innerWidth < window.RUSTDOC_MOBILE_BREAKPOINT) {
+        if (window.innerWidth < window.RUSTDOC_MOBILE_BREAKPOINT && oldScrollPosition !== null) {
             // This is to keep the scroll position on mobile.
             document.body.style.position = "";
             document.body.style.top = "";
             // The scroll position is lost when resetting the style, hence why we store it in
-            // `oldScroll`.
+            // `oldScrollPosition`.
             window.scrollTo(0, oldScrollPosition);
+            oldScrollPosition = null;
         }
         removeClass(document.documentElement, "source-sidebar-expanded");
         child.innerText = ">";
@@ -90,6 +93,17 @@ function toggleSidebar() {
     }
 }
 
+window.addEventListener("resize", () => {
+    if (window.innerWidth >= window.RUSTDOC_MOBILE_BREAKPOINT && oldScrollPosition !== null) {
+        // If the user opens the sidebar in "mobile" mode, and then grows the browser window,
+        // we need to switch away from mobile mode and make the main content area scrollable.
+        document.body.style.position = "";
+        document.body.style.top = "";
+        window.scrollTo(0, oldScrollPosition);
+        oldScrollPosition = null;
+    }
+});
+
 function createSidebarToggle() {
     const sidebarToggle = document.createElement("div");
     sidebarToggle.id = "sidebar-toggle";
-- 
cgit 1.4.1-3-g733a5