Auto merge of #85876 - jeanlucthumm:master, r=GuillaumeGomez

Add `go_to_first` query param to jump to first result

Fixes #84214

Note that while the issue initially wanted to navigate to an entry on exact match, the discussion settled on using a query parameter (`&go_to_first=true`) instead, regardless of exact or partial match.

Demonstration is attached

https://user-images.githubusercontent.com/4934853/120258768-7ff28980-c247-11eb-8c8f-1a2ceb242788.mp4

src/doc/rustdoc/src/SUMMARY.md

@@ -10,5 +10,6 @@
 - [Lints](lints.md)
 - [Advanced features](advanced-features.md)
 - [Unstable features](unstable-features.md)
+- [Website features](website-features.md)
 - [Passes](passes.md)
 - [References](references.md)

src/doc/rustdoc/src/website-features.md

@@ -0,0 +1,25 @@
+# Website features
+
+These features are about using the website generated by `rustdoc`.
+
+## Custom search engines
+
+If you find yourself often referencing online Rust docs you might enjoy using a custom search
+engine. This allows you to use the navigation bar directly to search a `rustdoc` website.
+Most browsers support this feature by letting you define a URL template containing `%s`
+which will be substituted for the search term. As an example, for the standard library you could use
+this template:
+
+```text
+https://doc.rust-lang.org/stable/std/?search=%s
+```
+
+Note that this will take you to a results page listing all matches. If you want to navigate to the first
+result right away (which is often the best match) use the following instead:
+
+```text
+https://doc.rust-lang.org/stable/std/?search=%s&go_to_first=true
+```
+
+This URL adds the `go_to_first=true` query parameter which can be appended to any `rustdoc` search URL
+to automatically go to the first result.

src/librustdoc/html/static/search.js

@@ -1058,14 +1058,14 @@ window.initSearch = function(rawSearchIndex) {
         return "<button>" + text + " <div class=\"count\">(" + nbElems + ")</div></button>";
     }
 
-    function showResults(results) {
+    function showResults(results, go_to_first) {
         var search = searchState.outputElement();
-        if (results.others.length === 1
+        if (go_to_first || (results.others.length === 1
             && getSettingValue("go-to-only-result") === "true"
             // By default, the search DOM element is "empty" (meaning it has no children not
             // text content). Once a search has been run, it won't be empty, even if you press
             // ESC or empty the search input (which also "cancels" the search).
-            && (!search.firstChild || search.firstChild.innerText !== searchState.loadingText))
+            && (!search.firstChild || search.firstChild.innerText !== searchState.loadingText)))
         {
             var elem = document.createElement("a");
             elem.href = results.others[0].href;
@@ -1242,7 +1242,7 @@ window.initSearch = function(rawSearchIndex) {
         }
 
         var filterCrates = getFilterCrates();
-        showResults(execSearch(query, index, filterCrates));
+        showResults(execSearch(query, index, filterCrates), params.go_to_first);
     }
 
     function buildIndex(rawSearchIndex) {