rustdoc: fix resize trouble with mobile

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

@@ -1305,6 +1305,7 @@ href="https://doc.rust-lang.org/${channel}/rustdoc/how-to-read-rustdoc.html\
     // at most 400px. Otherwise, it would start out at the default size, then
     // grabbing the resize handle would suddenly cause it to jank to
     // its contraint-generated maximum.
+    const RUSTDOC_MOBILE_BREAKPOINT = 700;
     const BODY_MIN = 400;
     // At half-way past the minimum size, vanish the sidebar entirely
     const SIDEBAR_VANISH_THRESHOLD = SIDEBAR_MIN / 2;
@@ -1474,6 +1475,9 @@ href="https://doc.rust-lang.org/${channel}/rustdoc/how-to-read-rustdoc.html\
     }
     // Respond to the window resize event.
     window.addEventListener("resize", () => {
+        if (window.innerWidth < RUSTDOC_MOBILE_BREAKPOINT) {
+            return;
+        }
         stopResize();
         if (desiredSidebarSize >= (window.innerWidth - BODY_MIN)) {
             changeSidebarSize(window.innerWidth - BODY_MIN);

tests/rustdoc-gui/sidebar-resize-window.goml

@@ -18,6 +18,10 @@ wait-for-property: (".sidebar", {"clientWidth": 500}, [NEAR])
 // make the window small enough that the sidebar has to shrink
 set-window-size: (750, 600)
 wait-for-property: (".sidebar", {"clientWidth": 350}, [NEAR])
+assert-local-storage: {"rustdoc-desktop-sidebar-width": "350"}
+set-window-size: (400, 600)
+wait-for-css: (".sidebar", {"display": "block", "left": "-1000px"})
+assert-local-storage: {"rustdoc-desktop-sidebar-width": "350"}
 
 // grow the window again to make the sidebar bigger
 set-window-size: (1280, 600)