Let SWUP handle in-doc links that carry a fragment

a66397f restricted SWUP's linkSelector to `[href$=".html"]` so that links to
non-HTML files (downloads such as `.mmd`) would no longer be routed through
SWUP and break the page swap (elixir-lang#2182). But `$=` matches only hrefs that *end*
in `.html`, which also excluded in-doc anchored links -- function references
like `Foo.html#fun/1` and the sidebar's per-function entries -- dropping them
back to a full page reload.

Match `.html` whether or not a fragment follows, via
`:is([href$=".html"], [href*=".html#"])`. Non-HTML files stay excluded, so
this keeps elixir-lang#2182 fixed while restoring smooth navigation for anchored links.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: garazdawi

assets/js/swup.js

@@ -38,6 +38,14 @@ const maybePreventSwup = (visit, {page}) => {
   }
 }
 
+// Only let SWUP intercept links to local .html documentation pages; routing
+// downloads or other non-HTML files through it breaks the page swap (#2182).
+// The `.html#fragment` branch keeps in-doc anchored links — function references
+// like `Foo.html#fun/1`, sidebar entries — on the SWUP path, which a plain
+// `[href$=".html"]` (matching only hrefs that *end* in .html) would drop.
+export const LINK_SELECTOR =
+  'a[href]:not([href^="/"]):not([href^="http"]):is([href$=".html"], [href*=".html#"])'
+
 window.addEventListener('DOMContentLoaded', emitExdocLoaded)
 
 if (!isEmbedded && window.location.protocol !== 'file:') {
@@ -50,7 +58,7 @@ if (!isEmbedded && window.location.protocol !== 'file:') {
             path === window.location.pathname + '.html' ||
             isCrossBuild(window.location.pathname, path)
     },
-    linkSelector: 'a[href]:not([href^="/"]):not([href^="http"])[href$=".html"]',
+    linkSelector: LINK_SELECTOR,
     hooks: {
       'page:load': maybePreventSwup,
       'page:view': emitExdocLoaded

assets/test/swup.spec.js

@@ -1,4 +1,7 @@
-import { isCrossBuild } from '../js/swup'
+import { el } from '../js/helpers'
+import { isCrossBuild, LINK_SELECTOR } from '../js/swup'
+
+const linkMatches = (href) => el('a', {href}).matches(LINK_SELECTOR)
 
 // SWUP resolves every href against the current page before it reaches
 // isCrossBuild, so the inputs here are always absolute pathnames -- a relative
@@ -21,4 +24,19 @@ describe('swup', () => {
       expect(isCrossBuild('/doc/apps/erts/atomics.html', '/doc/index.html')).toBe(true)
     })
   })
+
+  describe('LINK_SELECTOR', () => {
+    it('matches in-doc .html pages, with or without a fragment', () => {
+      expect(linkMatches('Foo.html')).toBe(true)
+      expect(linkMatches('String.Chars.html#trim/1')).toBe(true)
+      expect(linkMatches('module.html#content')).toBe(true)
+    })
+
+    it('ignores non-HTML files (#2182) and non-relative links', () => {
+      expect(linkMatches('ecto_erd.mmd')).toBe(false)
+      expect(linkMatches('ecto_erd.mmd#anchor')).toBe(false)
+      expect(linkMatches('/absolute.html')).toBe(false)
+      expect(linkMatches('https://hexdocs.pm/ecto/Ecto.html')).toBe(false)
+    })
+  })
 })