Fix ordering inside searchindex.js not being deterministic

Fixes sphinx-doc#11622

CHANGES.rst

@@ -18,6 +18,7 @@ Bugs fixed
 
 * #11668: Raise a useful error when ``theme.conf`` is missing.
   Patch by Vinay Sajip.
+* #11622: Fix ordering inside searchindex.js not being deterministic.
 
 Testing
 -------

sphinx/search/__init__.py

@@ -162,7 +162,7 @@ class _JavaScriptIndex:
     SUFFIX = ')'
 
     def dumps(self, data: Any) -> str:
-        return self.PREFIX + json.dumps(data) + self.SUFFIX
+        return self.PREFIX + json.dumps(data, sort_keys=True) + self.SUFFIX
 
     def loads(self, s: str) -> Any:
         data = s[len(self.PREFIX):-len(self.SUFFIX)]

tests/test_search.py

@@ -304,3 +304,23 @@ def test_parallel(app):
     app.build()
     index = load_searchindex(app.outdir / 'searchindex.js')
     assert index['docnames'] == ['index', 'nosearch', 'tocitem']
+
+
+@pytest.mark.sphinx(testroot='search')
+def test_search_index_is_deterministic(app):
+    app.builder.build_all()
+    index = load_searchindex(app.outdir / 'searchindex.js')
+
+    def check_if_dicts_are_sorted(item):
+        if isinstance(item, dict):
+            assert list(item.keys()) == sorted(item.keys())
+            for child in item.values():
+                check_if_dicts_are_sorted(child)
+        # Lists in the search index cannot be sorted: for some lists, their
+        # position inside the list is referenced elsewhere in the index, so if
+        # we were to sort lists, the search index would break.
+        elif isinstance(item, list):
+            for child in item:
+                check_if_dicts_are_sorted(child)
+
+    check_if_dicts_are_sorted(index)