rustdoc: factor JS mobile scroll lock into its own function

#98775 (comment)

Author: notriddle

src/librustdoc/html/static/js/main.js

@@ -733,37 +733,51 @@ function loadCss(cssFileName) {
 
     let oldSidebarScrollPosition = null;
 
-    function showSidebar() {
+    // Scroll locking used both here and in source-script.js
+
+    window.rustdocMobileScrollLock = function() {
         const mobile_topbar = document.querySelector(".mobile-topbar");
-        if (window.innerWidth < window.RUSTDOC_MOBILE_BREAKPOINT && mobile_topbar) {
+        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`;
-            mobile_topbar.style.top = `${oldSidebarScrollPosition}px`;
-            mobile_topbar.style.position = "relative";
+            if (mobile_topbar) {
+                mobile_topbar.style.top = `${oldSidebarScrollPosition}px`;
+                mobile_topbar.style.position = "relative";
+            }
         } else {
             oldSidebarScrollPosition = null;
         }
-        const sidebar = document.getElementsByClassName("sidebar")[0];
-        addClass(sidebar, "shown");
-    }
+    };
 
-    function hideSidebar() {
+    window.rustdocMobileScrollUnlock = function() {
         const mobile_topbar = document.querySelector(".mobile-topbar");
-        if (oldSidebarScrollPosition !== null && mobile_topbar) {
+        if (oldSidebarScrollPosition !== null) {
             // This is to keep the scroll position on mobile.
             document.body.style.width = "";
             document.body.style.position = "";
             document.body.style.top = "";
-            mobile_topbar.style.top = "";
-            mobile_topbar.style.position = "";
+            if (mobile_topbar) {
+                mobile_topbar.style.top = "";
+                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;
         }
+    };
+
+    function showSidebar() {
+        window.rustdocMobileScrollLock();
+        const sidebar = document.getElementsByClassName("sidebar")[0];
+        addClass(sidebar, "shown");
+    }
+
+    function hideSidebar() {
+        window.rustdocMobileScrollUnlock();
         const sidebar = document.getElementsByClassName("sidebar")[0];
         removeClass(sidebar, "shown");
     }

src/librustdoc/html/static/js/source-script.js

@@ -10,7 +10,6 @@
 (function() {
 
 const rootPath = document.getElementById("rustdoc-vars").attributes["data-root-path"].value;
-let oldScrollPosition = null;
 
 const NAME_OFFSET = 0;
 const DIRS_OFFSET = 1;
@@ -70,44 +69,18 @@ function createDirEntry(elem, parent, fullPath, hasFoundFile) {
 function toggleSidebar() {
     const child = this.parentNode.children[0];
     if (child.innerText === ">") {
-        if (window.innerWidth < window.RUSTDOC_MOBILE_BREAKPOINT) {
-            // This is to keep the scroll position on mobile.
-            oldScrollPosition = window.scrollY;
-            document.body.style.position = "fixed";
-            document.body.style.top = `-${oldScrollPosition}px`;
-        } else {
-            oldScrollPosition = null;
-        }
+        window.rustdocMobileScrollLock();
         addClass(document.documentElement, "source-sidebar-expanded");
         child.innerText = "<";
         updateLocalStorage("source-sidebar-show", "true");
     } else {
-        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
-            // `oldScrollPosition`.
-            window.scrollTo(0, oldScrollPosition);
-            oldScrollPosition = null;
-        }
+        window.rustdocMobileScrollUnlock();
         removeClass(document.documentElement, "source-sidebar-expanded");
         child.innerText = ">";
         updateLocalStorage("source-sidebar-show", "false");
     }
 }
 
-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";
@@ -125,7 +98,7 @@ function createSidebarToggle() {
     return sidebarToggle;
 }
 
-// This function is called from "source-files.js", generated in `html/render/mod.rs`.
+// This function is called from "source-files.js", generated in `html/render/write_shared.rs`.
 // eslint-disable-next-line no-unused-vars
 function createSourceSidebar() {
     const container = document.querySelector("nav.sidebar");