Rollup merge of rust-lang#72968 - integer32llc:docs-arrow-keys, r=GuillaumeGomez

Only highlight doc search results via mouseover if mouse has moved

## What happens

- Go to https://doc.rust-lang.org/stable/std/index.html
- Put your mouse cursor somewhere in the middle where search results will appear and then don't move the mouse
- Press 's' to focus the search box
- Type a query that brings up enough search results to go under where your mouse cursor is
- Press the down arrow
- The search result that is one below where your mouse cursor is will be highlighted.

## What I expected

When not currently using the mouse, I expect doing a search and then pressing the down arrow to always highlight the first search result immediately below the search box.

## The fix

This feels a bit hacky to me; I'm open to other solutions. This introduces a global JS var that keeps track of whether the person searching has moved their mouse after doing a search or not, and only uses the mouse position to highlight search results if the person HAS moved the mouse AFTER doing a search.

Author: tmandry

src/librustdoc/html/static/main.js

@@ -100,6 +100,8 @@ function defocusSearchBar() {
     // 2 for "In Return Types"
     var currentTab = 0;
 
+    var mouseMovedAfterSearch = true;
+
     var titleBeforeSearch = document.title;
 
     function clearInputTimeout() {
@@ -162,6 +164,7 @@ function defocusSearchBar() {
         }
         addClass(main, "hidden");
         removeClass(search, "hidden");
+        mouseMovedAfterSearch = false;
     }
 
     function hideSearchResults(search) {
@@ -424,6 +427,12 @@ function defocusSearchBar() {
     document.addEventListener("keypress", handleShortcut);
     document.addEventListener("keydown", handleShortcut);
 
+    function resetMouseMoved(ev) {
+        mouseMovedAfterSearch = true;
+    }
+
+    document.addEventListener("mousemove", resetMouseMoved);
+
     var handleSourceHighlight = (function() {
         var prev_line_id = 0;
 
@@ -1353,20 +1362,22 @@ function defocusSearchBar() {
                 }
             };
             var mouseover_func = function(e) {
-                var el = e.target;
-                // to retrieve the real "owner" of the event.
-                while (el.tagName !== "TR") {
-                    el = el.parentNode;
-                }
-                clearTimeout(hoverTimeout);
-                hoverTimeout = setTimeout(function() {
-                    onEachLazy(document.getElementsByClassName("search-results"), function(e) {
-                        onEachLazy(e.getElementsByClassName("result"), function(i_e) {
-                            removeClass(i_e, "highlighted");
+                if (mouseMovedAfterSearch) {
+                    var el = e.target;
+                    // to retrieve the real "owner" of the event.
+                    while (el.tagName !== "TR") {
+                        el = el.parentNode;
+                    }
+                    clearTimeout(hoverTimeout);
+                    hoverTimeout = setTimeout(function() {
+                        onEachLazy(document.getElementsByClassName("search-results"), function(e) {
+                            onEachLazy(e.getElementsByClassName("result"), function(i_e) {
+                                removeClass(i_e, "highlighted");
+                            });
                         });
-                    });
-                    addClass(el, "highlighted");
-                }, 20);
+                        addClass(el, "highlighted");
+                    }, 20);
+                }
             };
             onEachLazy(document.getElementsByClassName("search-results"), function(e) {
                 onEachLazy(e.getElementsByClassName("result"), function(i_e) {