FIX: In-page anchor links were broken in subfolder setups (#18250)

The key fix in this commit is that it removes `this.replaceState(path)` for anchor-only URLs. We still intercept those routing changes to properly calculate the scroll position of the anchor via `jumpToElement`, but we no longer use the Ember router to override the browser's history. This fixes the subfolder issue and also lets the browser maintain its history correctly.

The commit also includes a small refactor to the `jumpToElement` helper to facilitate stubbing in tests.

app/assets/javascripts/discourse/app/lib/intercept-click.js

@@ -27,7 +27,7 @@ export default function interceptClick(e) {
 
   if (
     !href ||
-    href === "#" ||
+    href.startsWith("#") ||
     currentTarget.getAttribute("target") ||
     currentTarget.dataset.emberAction ||
     currentTarget.dataset.autoRoute ||

app/assets/javascripts/discourse/app/lib/static-route-builder.js

@@ -1,4 +1,4 @@
-import DiscourseURL, { jumpToElement } from "discourse/lib/url";
+import DiscourseURL from "discourse/lib/url";
 import DiscourseRoute from "discourse/routes/discourse";
 import I18n from "I18n";
 import StaticPage from "discourse/models/static-page";
@@ -25,7 +25,7 @@ export default function (page) {
 
     activate() {
       this._super(...arguments);
-      jumpToElement(document.location.hash.slice(1));
+      DiscourseURL.jumpToElement(document.location.hash.slice(1));
     },
 
     model() {

app/assets/javascripts/discourse/app/lib/url.js

@@ -73,29 +73,6 @@ let _jumpScheduled = false;
 let _transitioning = false;
 let lockOn = null;
 
-export function jumpToElement(elementId) {
-  if (_jumpScheduled || isEmpty(elementId)) {
-    return;
-  }
-
-  const selector = `#main #${elementId}, a[name=${elementId}]`;
-  _jumpScheduled = true;
-
-  schedule("afterRender", function () {
-    if (lockOn) {
-      lockOn.clearLock();
-    }
-
-    lockOn = new LockOn(selector, {
-      finished() {
-        _jumpScheduled = false;
-        lockOn = null;
-      },
-    });
-    lockOn.lock();
-  });
-}
-
 const DiscourseURL = EmberObject.extend({
   isJumpScheduled() {
     return _transitioning || _jumpScheduled;
@@ -237,8 +214,8 @@ const DiscourseURL = EmberObject.extend({
     // Scroll to the same page, different anchor
     const m = /^#(.+)$/.exec(path);
     if (m) {
-      jumpToElement(m[1]);
+      this.jumpToElement(m[1]);
-      return this.replaceState(path);
+      return;
     }
 
     const oldPath = this.router.currentURL;
@@ -479,9 +456,33 @@ const DiscourseURL = EmberObject.extend({
     transition._discourse_original_url = path;
 
     const promise = transition.promise || transition;
-    promise.then(() => jumpToElement(elementId));
+    promise.then(() => this.jumpToElement(elementId));
+  },
+
+  jumpToElement(elementId) {
+    if (_jumpScheduled || isEmpty(elementId)) {
+      return;
+    }
+
+    const selector = `#main #${elementId}, a[name=${elementId}]`;
+    _jumpScheduled = true;
+
+    schedule("afterRender", function () {
+      if (lockOn) {
+        lockOn.clearLock();
+      }
+
+      lockOn = new LockOn(selector, {
+        finished() {
+          _jumpScheduled = false;
+          lockOn = null;
         },
       });
+      lockOn.lock();
+    });
+  },
+});
+
 let _urlInstance = DiscourseURL.create();
 
 export function setURLContainer(container) {

app/assets/javascripts/discourse/tests/unit/lib/url-test.js

@@ -153,4 +153,13 @@ module("Unit | Utility | url", function () {
       )
     );
   });
+
+  test("anchor handling", async function (assert) {
+    sinon.stub(DiscourseURL, "jumpToElement");
+    DiscourseURL.routeTo("#heading1");
+    assert.ok(
+      DiscourseURL.jumpToElement.calledWith("heading1"),
+      "in-page anchors call jumpToElement"
+    );
+  });
 });