Restore correct parallel search index building

sphinx/builders/html/__init__.py

@@ -655,10 +655,6 @@ def get_doc_context(self, docname: str, body: str, metatags: str) -> dict[str, A
         }
 
     def write_doc(self, docname: str, doctree: nodes.document) -> None:
-        title_node = self.env.longtitles.get(docname)
-        title = self.render_partial(title_node)['title'] if title_node else ''
-        self.index_page(docname, doctree, title)
-
         destination = StringOutput(encoding='utf-8')
         doctree.settings = self.docsettings
 
@@ -678,6 +674,9 @@ def write_doc(self, docname: str, doctree: nodes.document) -> None:
     def write_doc_serialized(self, docname: str, doctree: nodes.document) -> None:
         self.imgpath = relative_uri(self.get_target_uri(docname), self.imagedir)
         self.post_process_images(doctree)
+        title_node = self.env.longtitles.get(docname)
+        title = self.render_partial(title_node)['title'] if title_node else ''
+        self.index_page(docname, doctree, title)
 
     def finish(self) -> None:
         self.finish_tasks.add_task(self.gen_indices)

tests/test_search.py

@@ -286,3 +286,10 @@ def test_nosearch(app):
     assert 'latex' not in index['terms']
     assert 'zfs' in index['terms']
     assert index['terms']['zfs'] == []  # zfs on nosearch.rst is not registered to index
+
+
+@pytest.mark.sphinx(testroot='search', parallel=3, freshenv=True)
+def test_parallel(app):
+    app.build()
+    index = load_searchindex(app.outdir / 'searchindex.js')
+    assert index['docnames'] == ['index', 'nosearch', 'tocitem']