Use explicit class instead of :target

Turbo Drive breaks the browser's back / forward buttons when navigating
to a history entry that was not added by Turbo Drive.  (The URL in the
address bar changes, but the page itself does not.)  Therefore, this
commit abandons working around Turbo Drive to fix `:target` behavior,
and adds an explicit `.target` class in response to navigation events
instead.

lib/rdoc/generator/template/rails/resources/css/main.css

@@ -767,7 +767,7 @@ html {
   white-space: pre-wrap;
 }
 
-:target .method__signature code::before {
+.target .method__signature code::before {
   content: " ";
 
   position: absolute;

lib/rdoc/generator/template/rails/resources/js/main.js

@@ -56,24 +56,22 @@ document.addEventListener("turbo:click", ({ target }) => {
   addEventListener("turbo:render", function() {
     document.getElementById("results").scrollTop = scrollTop
   })
-})()
+})();
 
 
 // Turbo Drive interferes with the browser designating the `:target` element for
-// CSS. See https://github.com/hotwired/turbo/issues/592.
-//
-// Therefore, disable Turbo Drive for intra-page link clicks...
-document.addEventListener("turbo:click", event => {
-  const targetUrl = new URL(event.detail.url);
-  if (targetUrl.hash && targetUrl.href === new URL(targetUrl.hash, location).href) {
-    event.preventDefault();
-  }
-});
-// ...and, if appropriate, trigger an intra-page navigation after `turbo:load`.
-document.addEventListener("turbo:load", event => {
-  if (location.hash) {
-    const a = document.createElement("a");
-    a.href = location;
-    a.click();
-  }
-});
+// CSS (see https://github.com/hotwired/turbo/issues/592), so add an explicit
+// class instead.
+(function() {
+  const retarget = (url) => {
+    document.querySelector(".target")?.classList?.remove("target");
+    if (url.hash) {
+      document.getElementById(url.hash.substring(1))?.classList?.add("target");
+    }
+  };
+
+  // Unlike normal navigation, Turbo Drive fires the `hashchange` _before_
+  // `location` is changed, so we must use the `newURL` property.
+  window.addEventListener("hashchange", ({ newURL }) => retarget(new URL(newURL)));
+  document.addEventListener("turbo:load", event => retarget(location));
+})();