fix: scope alternate link dedupeKey by href when type is used (#760)

Backport of #759 to v2.

Multiple RSS/Atom alternate links sharing the same `type` but with
different `href` values were being collapsed into one tag because the
dedupe key was built from `type` alone. Include `href` in the key for
type-based alternates so distinct feeds are preserved. `hreflang`
precedence is unchanged.

Fixes #758

Author: harlan-zw

packages/unhead/src/utils/dedupe.ts

@@ -31,10 +31,10 @@ export function dedupeKey<T extends HeadTag>(tag: T): string | undefined {
 
   // dedupe alternate links with hreflang/type by that attribute
   if (name === 'link' && props.rel === 'alternate') {
-    const altKey = props.hreflang || props.type
-    if (altKey) {
-      return `alternate:${altKey}`
-    }
+    if (props.hreflang)
+      return `alternate:${props.hreflang}`
+    if (props.type)
+      return `alternate:${props.type}:${props.href || ''}`
   }
 
   if (props.charset)

packages/unhead/test/unit/server/deduping.test.ts

@@ -644,7 +644,7 @@ describe('dedupe', () => {
     expect(headTags).toContain('hreflang="fr"')
   })
 
-  it('dedupes RSS feeds with same type', async () => {
+  it('dedupes RSS feeds with same type and same href on rehydration', async () => {
     const head = createServerHeadWithContext()
     head.push({
       link: [
@@ -653,13 +653,44 @@ describe('dedupe', () => {
     })
     head.push({
       link: [
-        { rel: 'alternate', type: 'application/rss+xml', href: 'https://example.com/feed2.xml', title: 'RSS Feed 2' },
+        { rel: 'alternate', type: 'application/rss+xml', href: 'https://example.com/feed.xml', title: 'RSS Feed' },
       ],
     })
     const { headTags } = await renderSSRHead(head)
     expect(headTags.split('rel="alternate"').length).toBe(2)
+    expect(headTags).toContain('feed.xml')
+  })
+
+  it('keeps multiple RSS feeds with same type and different hrefs (#758)', async () => {
+    const head = createServerHeadWithContext()
+    head.push({
+      link: [
+        { rel: 'alternate', type: 'application/rss+xml', href: 'https://example.com/feed.xml', title: 'RSS Feed' },
+        { rel: 'alternate', type: 'application/rss+xml', href: 'https://example.com/feed2.xml', title: 'RSS Feed 2' },
+      ],
+    })
+    const { headTags } = await renderSSRHead(head)
+    expect(headTags.split('rel="alternate"').length).toBe(3)
+    expect(headTags).toContain('feed.xml')
+    expect(headTags).toContain('feed2.xml')
+  })
+
+  it('keeps multiple RSS feeds across separate head pushes (#758)', async () => {
+    const head = createServerHeadWithContext()
+    head.push({
+      link: [
+        { rel: 'alternate', type: 'application/rss+xml', href: 'https://example.com/feed.xml', title: 'RSS Feed' },
+      ],
+    })
+    head.push({
+      link: [
+        { rel: 'alternate', type: 'application/rss+xml', href: 'https://example.com/feed2.xml', title: 'RSS Feed 2' },
+      ],
+    })
+    const { headTags } = await renderSSRHead(head)
+    expect(headTags.split('rel="alternate"').length).toBe(3)
+    expect(headTags).toContain('feed.xml')
     expect(headTags).toContain('feed2.xml')
-    expect(headTags).not.toContain('feed.xml"')
   })
 
   it('allows RSS and Atom feeds to coexist', async () => {