fix: parse template params in titleTemplate functions

Fixes #282

packages/unhead/src/plugins/templateParams.ts

@@ -1,5 +1,5 @@
 import { defineHeadPlugin, processTemplateParams } from '@unhead/shared'
-import type { TemplateParams } from '@unhead/schema'
+import type {HeadTag, TemplateParams} from '@unhead/schema'
 
 const SupportedAttrs = {
   meta: 'content',
@@ -60,5 +60,20 @@ export default defineHeadPlugin(head => ({
       head._templateParams = params
       head._separator = sep
     },
+    'tags:afterResolve': ({ tags }) => {
+      // we need to re-process in case then user had a function as the titleTemplate
+      // TODO drop support for function in v2
+      let title: HeadTag | undefined
+      for (let i = 0; i < tags.length; i += 1) {
+        const tag = tags[i]
+
+        if (tag.tag === 'title' && tag.processTemplateParams !== false) {
+          title = tag
+        }
+      }
+      if (title?.textContent) {
+        title.textContent = processTemplateParams(title.textContent, head._templateParams!, head._separator!)
+      }
+    },
   },
 }))

test/unhead/ssr/titleTemplate.test.ts

@@ -84,4 +84,22 @@ describe('titleTemplate', () => {
       `""`,
     )
   })
+  it('function titleTemplate with templateParams', async () => {
+    const head = createHead()
+    head.push({
+      titleTemplate: () => '%s %separator %subPage% %separator %site.name',
+      title: 'test %foo',
+      templateParams: {
+        site: {
+          name: 'test',
+        },
+        subPage: 'subPage',
+        foo: 'foo',
+      },
+    })
+    const { headTags } = await renderSSRHead(head)
+    expect(headTags).toMatchInlineSnapshot(
+      `"<title>test foo | subPage% | test</title>"`,
+    )
+  })
 })