We are currently solving the following issue within our repository. Here is the issue text:
--- BEGIN ISSUE ---
Getting an item after slicing ElasticSearchResults object gives wrong result
For example, let's say we have a list of results with the items A, B, C and D

If you run results[0]. You get A
If you run results[2:]. You get [C, D]
But if you run results[2:][0]. You will get A (you should get C)

Fix coming shortly


--- END ISSUE ---

Below are some code segments, each from a relevant file. One or more of these files may contain bugs.
--- BEGIN FILES ---
Path: `wagtail/wagtailsearch/backends/base.py`
Content:
```
1 from six import text_type
2 
3 from django.db.models.query import QuerySet
4 from django.db.models.lookups import Lookup
5 from django.db.models.sql.where import SubqueryConstraint, WhereNode
6 
7 from wagtail.wagtailsearch.index import class_is_indexed
8 
9 
10 class FilterError(Exception):
11     pass
12 
13 
14 class FieldError(Exception):
15     pass
16 
17 
18 class BaseSearchQuery(object):
19     def __init__(self, queryset, query_string, fields=None):
20         self.queryset = queryset
21         self.query_string = query_string
22         self.fields = fields
23 
24     def _get_searchable_field(self, field_attname):
25         # Get field
26         field = dict(
27             (field.get_attname(self.queryset.model), field)
28             for field in self.queryset.model.get_searchable_search_fields()
29         ).get(field_attname, None)
30 
31         return field
32 
33     def _get_filterable_field(self, field_attname):
34         # Get field
35         field = dict(
36             (field.get_attname(self.queryset.model), field)
37             for field in self.queryset.model.get_filterable_search_fields()
38         ).get(field_attname, None)
39 
40         return field
41 
42     def _process_lookup(self, field, lookup, value):
43         raise NotImplementedError
44 
45     def _connect_filters(self, filters, connector, negated):
46         raise NotImplementedError
47 
48     def _process_filter(self, field_attname, lookup, value):
49         # Get the field
50         field = self._get_filterable_field(field_attname)
51 
52         if field is None:
53             raise FieldError('Cannot filter search results with field "' + field_attname + '". Please add index.FilterField(\'' + field_attname + '\') to ' + self.queryset.model.__name__ + '.search_fields.')
54 
55         # Process the lookup
56         result = self._process_lookup(field, lookup, value)
57 
58         if result is None:
59             raise FilterError('Could not apply filter on search results: "' + field_attname + '__' + lookup + ' = ' + text_type(value) + '". Lookup "' + lookup + '"" not recognosed.')
60 
61         return result
62 
63     def _get_filters_from_where_node(self, where_node):
64         # Check if this is a leaf node
65         if isinstance(where_node, Lookup):
66             field_attname = where_node.lhs.target.attname
67             lookup = where_node.lookup_name
68             value = where_node.rhs
69 
70             # Process the filter
71             return self._process_filter(field_attname, lookup, value)
72 
73         elif isinstance(where_node, SubqueryConstraint):
74             raise FilterError('Could not apply filter on search results: Subqueries are not allowed.')
75 
76         elif isinstance(where_node, WhereNode):
77             # Get child filters
78             connector = where_node.connector
79             child_filters = [self._get_filters_from_where_node(child) for child in where_node.children]
80             child_filters = [child_filter for child_filter in child_filters if child_filter]
81 
82             return self._connect_filters(child_filters, connector, where_node.negated)
83 
84         else:
85             raise FilterError('Could not apply filter on search results: Unknown where node: ' + str(type(where_node)))
86 
87     def _get_filters_from_queryset(self):
88         return self._get_filters_from_where_node(self.queryset.query.where)
89 
90 
91 class BaseSearchResults(object):
92     def __init__(self, backend, query, prefetch_related=None):
93         self.backend = backend
94         self.query = query
95         self.prefetch_related = prefetch_related
96         self.start = 0
97         self.stop = None
98         self._results_cache = None
99         self._count_cache = None
100 
101     def _set_limits(self, start=None, stop=None):
102         if stop is not None:
103             if self.stop is not None:
104                 self.stop = min(self.stop, self.start + stop)
105             else:
106                 self.stop = self.start + stop
107 
108         if start is not None:
109             if self.stop is not None:
110                 self.start = min(self.stop, self.start + start)
111             else:
112                 self.start = self.start + start
113 
114     def _clone(self):
115         klass = self.__class__
116         new = klass(self.backend, self.query, prefetch_related=self.prefetch_related)
117         new.start = self.start
118         new.stop = self.stop
119         return new
120 
121     def _do_search(self):
122         raise NotImplementedError
123 
124     def _do_count(self):
125         raise NotImplementedError
126 
127     def results(self):
128         if self._results_cache is None:
129             self._results_cache = self._do_search()
130         return self._results_cache
131 
132     def count(self):
133         if self._count_cache is None:
134             if self._results_cache is not None:
135                 self._count_cache = len(self._results_cache)
136             else:
137                 self._count_cache = self._do_count()
138         return self._count_cache
139 
140     def __getitem__(self, key):
141         new = self._clone()
142 
143         if isinstance(key, slice):
144             # Set limits
145             start = int(key.start) if key.start else None
146             stop = int(key.stop) if key.stop else None
147             new._set_limits(start, stop)
148 
149             # Copy results cache
150             if self._results_cache is not None:
151                 new._results_cache = self._results_cache[key]
152 
153             return new
154         else:
155             if self._results_cache is not None:
156                 return self._results_cache[key]
157 
158             new.start = key
159             new.stop = key + 1
160             return list(new)[0]
161 
162     def __iter__(self):
163         return iter(self.results())
164 
165     def __len__(self):
166         return len(self.results())
167 
168     def __repr__(self):
169         data = list(self[:21])
170         if len(data) > 20:
171             data[-1] = "...(remaining elements truncated)..."
172         return repr(data)
173 
174 
175 class BaseSearch(object):
176     def __init__(self, params):
177         pass
178 
179     def reset_index(self):
180         raise NotImplementedError
181 
182     def add_type(self, model):
183         raise NotImplementedError
184 
185     def refresh_index(self):
186         raise NotImplementedError
187 
188     def add(self, obj):
189         raise NotImplementedError
190 
191     def add_bulk(self, model, obj_list):
192         raise NotImplementedError
193 
194     def delete(self, obj):
195         raise NotImplementedError
196 
197     def _search(self, queryset, query_string, fields=None):
198         raise NotImplementedError
199 
200     def search(self, query_string, model_or_queryset, fields=None, filters=None, prefetch_related=None):
201         # Find model/queryset
202         if isinstance(model_or_queryset, QuerySet):
203             model = model_or_queryset.model
204             queryset = model_or_queryset
205         else:
206             model = model_or_queryset
207             queryset = model_or_queryset.objects.all()
208 
209         # Model must be a class that is in the index
210         if not class_is_indexed(model):
211             return []
212 
213         # Check that theres still a query string after the clean up
214         if query_string == "":
215             return []
216 
217         # Apply filters to queryset
218         if filters:
219             queryset = queryset.filter(**filters)
220 
221         # Prefetch related
222         if prefetch_related:
223             for prefetch in prefetch_related:
224                 queryset = queryset.prefetch_related(prefetch)
225 
226         # Search
227         return self._search(queryset, query_string, fields=fields)
228
```
--- END FILES ---

Please first localize the bug based on the issue statement, and then generate a patch according to the `git diff` format fenced by three backticks.

Here is an example:

```diff
diff --git a/examples/server_async.py b/examples/server_async.py
--- a/examples/server_async.py
+++ b/examples/server_async.py
@@ -313,4 +313,4 @@
 
 
 if __name__ == "__main__":
-    asyncio.run(run_async_server("."), debug=True)
+    asyncio.run(run_async_server(), debug=True)
diff --git a/examples/server_sync.py b/examples/server_sync.py
--- a/examples/server_sync.py
+++ b/examples/server_sync.py
@@ -313,5 +313,5 @@
 
 
 if __name__ == "__main__":
-    server = run_sync_server(".")
+    server = run_sync_server()
     server.shutdown()

```

diff --git a/wagtail/wagtailsearch/backends/base.py b/wagtail/wagtailsearch/backends/base.py
--- a/wagtail/wagtailsearch/backends/base.py
+++ b/wagtail/wagtailsearch/backends/base.py
@@ -155,8 +155,8 @@
             if self._results_cache is not None:
                 return self._results_cache[key]
 
-            new.start = key
-            new.stop = key + 1
+            new.start = self.start + key
+            new.stop = self.start + key + 1
             return list(new)[0]
 
     def __iter__(self):

{"golden_diff": "diff --git a/wagtail/wagtailsearch/backends/base.py b/wagtail/wagtailsearch/backends/base.py\n--- a/wagtail/wagtailsearch/backends/base.py\n+++ b/wagtail/wagtailsearch/backends/base.py\n@@ -155,8 +155,8 @@\n             if self._results_cache is not None:\n                 return self._results_cache[key]\n \n-            new.start = key\n-            new.stop = key + 1\n+            new.start = self.start + key\n+            new.stop = self.start + key + 1\n             return list(new)[0]\n \n     def __iter__(self):\n", "issue": "Getting an item after slicing ElasticSearchResults object gives wrong result\nFor example, let's say we have a list of results with the items A, B, C and D\n\nIf you run results[0]. You get A\nIf you run results[2:]. You get [C, D]\nBut if you run results[2:][0]. You will get A (you should get C)\n\nFix coming shortly\n\n", "before_files": [{"content": "from six import text_type\n\nfrom django.db.models.query import QuerySet\nfrom django.db.models.lookups import Lookup\nfrom django.db.models.sql.where import SubqueryConstraint, WhereNode\n\nfrom wagtail.wagtailsearch.index import class_is_indexed\n\n\nclass FilterError(Exception):\n    pass\n\n\nclass FieldError(Exception):\n    pass\n\n\nclass BaseSearchQuery(object):\n    def __init__(self, queryset, query_string, fields=None):\n        self.queryset = queryset\n        self.query_string = query_string\n        self.fields = fields\n\n    def _get_searchable_field(self, field_attname):\n        # Get field\n        field = dict(\n            (field.get_attname(self.queryset.model), field)\n            for field in self.queryset.model.get_searchable_search_fields()\n        ).get(field_attname, None)\n\n        return field\n\n    def _get_filterable_field(self, field_attname):\n        # Get field\n        field = dict(\n            (field.get_attname(self.queryset.model), field)\n            for field in self.queryset.model.get_filterable_search_fields()\n        ).get(field_attname, None)\n\n        return field\n\n    def _process_lookup(self, field, lookup, value):\n        raise NotImplementedError\n\n    def _connect_filters(self, filters, connector, negated):\n        raise NotImplementedError\n\n    def _process_filter(self, field_attname, lookup, value):\n        # Get the field\n        field = self._get_filterable_field(field_attname)\n\n        if field is None:\n            raise FieldError('Cannot filter search results with field \"' + field_attname + '\". Please add index.FilterField(\\'' + field_attname + '\\') to ' + self.queryset.model.__name__ + '.search_fields.')\n\n        # Process the lookup\n        result = self._process_lookup(field, lookup, value)\n\n        if result is None:\n            raise FilterError('Could not apply filter on search results: \"' + field_attname + '__' + lookup + ' = ' + text_type(value) + '\". Lookup \"' + lookup + '\"\" not recognosed.')\n\n        return result\n\n    def _get_filters_from_where_node(self, where_node):\n        # Check if this is a leaf node\n        if isinstance(where_node, Lookup):\n            field_attname = where_node.lhs.target.attname\n            lookup = where_node.lookup_name\n            value = where_node.rhs\n\n            # Process the filter\n            return self._process_filter(field_attname, lookup, value)\n\n        elif isinstance(where_node, SubqueryConstraint):\n            raise FilterError('Could not apply filter on search results: Subqueries are not allowed.')\n\n        elif isinstance(where_node, WhereNode):\n            # Get child filters\n            connector = where_node.connector\n            child_filters = [self._get_filters_from_where_node(child) for child in where_node.children]\n            child_filters = [child_filter for child_filter in child_filters if child_filter]\n\n            return self._connect_filters(child_filters, connector, where_node.negated)\n\n        else:\n            raise FilterError('Could not apply filter on search results: Unknown where node: ' + str(type(where_node)))\n\n    def _get_filters_from_queryset(self):\n        return self._get_filters_from_where_node(self.queryset.query.where)\n\n\nclass BaseSearchResults(object):\n    def __init__(self, backend, query, prefetch_related=None):\n        self.backend = backend\n        self.query = query\n        self.prefetch_related = prefetch_related\n        self.start = 0\n        self.stop = None\n        self._results_cache = None\n        self._count_cache = None\n\n    def _set_limits(self, start=None, stop=None):\n        if stop is not None:\n            if self.stop is not None:\n                self.stop = min(self.stop, self.start + stop)\n            else:\n                self.stop = self.start + stop\n\n        if start is not None:\n            if self.stop is not None:\n                self.start = min(self.stop, self.start + start)\n            else:\n                self.start = self.start + start\n\n    def _clone(self):\n        klass = self.__class__\n        new = klass(self.backend, self.query, prefetch_related=self.prefetch_related)\n        new.start = self.start\n        new.stop = self.stop\n        return new\n\n    def _do_search(self):\n        raise NotImplementedError\n\n    def _do_count(self):\n        raise NotImplementedError\n\n    def results(self):\n        if self._results_cache is None:\n            self._results_cache = self._do_search()\n        return self._results_cache\n\n    def count(self):\n        if self._count_cache is None:\n            if self._results_cache is not None:\n                self._count_cache = len(self._results_cache)\n            else:\n                self._count_cache = self._do_count()\n        return self._count_cache\n\n    def __getitem__(self, key):\n        new = self._clone()\n\n        if isinstance(key, slice):\n            # Set limits\n            start = int(key.start) if key.start else None\n            stop = int(key.stop) if key.stop else None\n            new._set_limits(start, stop)\n\n            # Copy results cache\n            if self._results_cache is not None:\n                new._results_cache = self._results_cache[key]\n\n            return new\n        else:\n            if self._results_cache is not None:\n                return self._results_cache[key]\n\n            new.start = key\n            new.stop = key + 1\n            return list(new)[0]\n\n    def __iter__(self):\n        return iter(self.results())\n\n    def __len__(self):\n        return len(self.results())\n\n    def __repr__(self):\n        data = list(self[:21])\n        if len(data) > 20:\n            data[-1] = \"...(remaining elements truncated)...\"\n        return repr(data)\n\n\nclass BaseSearch(object):\n    def __init__(self, params):\n        pass\n\n    def reset_index(self):\n        raise NotImplementedError\n\n    def add_type(self, model):\n        raise NotImplementedError\n\n    def refresh_index(self):\n        raise NotImplementedError\n\n    def add(self, obj):\n        raise NotImplementedError\n\n    def add_bulk(self, model, obj_list):\n        raise NotImplementedError\n\n    def delete(self, obj):\n        raise NotImplementedError\n\n    def _search(self, queryset, query_string, fields=None):\n        raise NotImplementedError\n\n    def search(self, query_string, model_or_queryset, fields=None, filters=None, prefetch_related=None):\n        # Find model/queryset\n        if isinstance(model_or_queryset, QuerySet):\n            model = model_or_queryset.model\n            queryset = model_or_queryset\n        else:\n            model = model_or_queryset\n            queryset = model_or_queryset.objects.all()\n\n        # Model must be a class that is in the index\n        if not class_is_indexed(model):\n            return []\n\n        # Check that theres still a query string after the clean up\n        if query_string == \"\":\n            return []\n\n        # Apply filters to queryset\n        if filters:\n            queryset = queryset.filter(**filters)\n\n        # Prefetch related\n        if prefetch_related:\n            for prefetch in prefetch_related:\n                queryset = queryset.prefetch_related(prefetch)\n\n        # Search\n        return self._search(queryset, query_string, fields=fields)\n", "path": "wagtail/wagtailsearch/backends/base.py"}], "after_files": [{"content": "from six import text_type\n\nfrom django.db.models.query import QuerySet\nfrom django.db.models.lookups import Lookup\nfrom django.db.models.sql.where import SubqueryConstraint, WhereNode\n\nfrom wagtail.wagtailsearch.index import class_is_indexed\n\n\nclass FilterError(Exception):\n    pass\n\n\nclass FieldError(Exception):\n    pass\n\n\nclass BaseSearchQuery(object):\n    def __init__(self, queryset, query_string, fields=None):\n        self.queryset = queryset\n        self.query_string = query_string\n        self.fields = fields\n\n    def _get_searchable_field(self, field_attname):\n        # Get field\n        field = dict(\n            (field.get_attname(self.queryset.model), field)\n            for field in self.queryset.model.get_searchable_search_fields()\n        ).get(field_attname, None)\n\n        return field\n\n    def _get_filterable_field(self, field_attname):\n        # Get field\n        field = dict(\n            (field.get_attname(self.queryset.model), field)\n            for field in self.queryset.model.get_filterable_search_fields()\n        ).get(field_attname, None)\n\n        return field\n\n    def _process_lookup(self, field, lookup, value):\n        raise NotImplementedError\n\n    def _connect_filters(self, filters, connector, negated):\n        raise NotImplementedError\n\n    def _process_filter(self, field_attname, lookup, value):\n        # Get the field\n        field = self._get_filterable_field(field_attname)\n\n        if field is None:\n            raise FieldError('Cannot filter search results with field \"' + field_attname + '\". Please add index.FilterField(\\'' + field_attname + '\\') to ' + self.queryset.model.__name__ + '.search_fields.')\n\n        # Process the lookup\n        result = self._process_lookup(field, lookup, value)\n\n        if result is None:\n            raise FilterError('Could not apply filter on search results: \"' + field_attname + '__' + lookup + ' = ' + text_type(value) + '\". Lookup \"' + lookup + '\"\" not recognosed.')\n\n        return result\n\n    def _get_filters_from_where_node(self, where_node):\n        # Check if this is a leaf node\n        if isinstance(where_node, Lookup):\n            field_attname = where_node.lhs.target.attname\n            lookup = where_node.lookup_name\n            value = where_node.rhs\n\n            # Process the filter\n            return self._process_filter(field_attname, lookup, value)\n\n        elif isinstance(where_node, SubqueryConstraint):\n            raise FilterError('Could not apply filter on search results: Subqueries are not allowed.')\n\n        elif isinstance(where_node, WhereNode):\n            # Get child filters\n            connector = where_node.connector\n            child_filters = [self._get_filters_from_where_node(child) for child in where_node.children]\n            child_filters = [child_filter for child_filter in child_filters if child_filter]\n\n            return self._connect_filters(child_filters, connector, where_node.negated)\n\n        else:\n            raise FilterError('Could not apply filter on search results: Unknown where node: ' + str(type(where_node)))\n\n    def _get_filters_from_queryset(self):\n        return self._get_filters_from_where_node(self.queryset.query.where)\n\n\nclass BaseSearchResults(object):\n    def __init__(self, backend, query, prefetch_related=None):\n        self.backend = backend\n        self.query = query\n        self.prefetch_related = prefetch_related\n        self.start = 0\n        self.stop = None\n        self._results_cache = None\n        self._count_cache = None\n\n    def _set_limits(self, start=None, stop=None):\n        if stop is not None:\n            if self.stop is not None:\n                self.stop = min(self.stop, self.start + stop)\n            else:\n                self.stop = self.start + stop\n\n        if start is not None:\n            if self.stop is not None:\n                self.start = min(self.stop, self.start + start)\n            else:\n                self.start = self.start + start\n\n    def _clone(self):\n        klass = self.__class__\n        new = klass(self.backend, self.query, prefetch_related=self.prefetch_related)\n        new.start = self.start\n        new.stop = self.stop\n        return new\n\n    def _do_search(self):\n        raise NotImplementedError\n\n    def _do_count(self):\n        raise NotImplementedError\n\n    def results(self):\n        if self._results_cache is None:\n            self._results_cache = self._do_search()\n        return self._results_cache\n\n    def count(self):\n        if self._count_cache is None:\n            if self._results_cache is not None:\n                self._count_cache = len(self._results_cache)\n            else:\n                self._count_cache = self._do_count()\n        return self._count_cache\n\n    def __getitem__(self, key):\n        new = self._clone()\n\n        if isinstance(key, slice):\n            # Set limits\n            start = int(key.start) if key.start else None\n            stop = int(key.stop) if key.stop else None\n            new._set_limits(start, stop)\n\n            # Copy results cache\n            if self._results_cache is not None:\n                new._results_cache = self._results_cache[key]\n\n            return new\n        else:\n            if self._results_cache is not None:\n                return self._results_cache[key]\n\n            new.start = self.start + key\n            new.stop = self.start + key + 1\n            return list(new)[0]\n\n    def __iter__(self):\n        return iter(self.results())\n\n    def __len__(self):\n        return len(self.results())\n\n    def __repr__(self):\n        data = list(self[:21])\n        if len(data) > 20:\n            data[-1] = \"...(remaining elements truncated)...\"\n        return repr(data)\n\n\nclass BaseSearch(object):\n    def __init__(self, params):\n        pass\n\n    def reset_index(self):\n        raise NotImplementedError\n\n    def add_type(self, model):\n        raise NotImplementedError\n\n    def refresh_index(self):\n        raise NotImplementedError\n\n    def add(self, obj):\n        raise NotImplementedError\n\n    def add_bulk(self, model, obj_list):\n        raise NotImplementedError\n\n    def delete(self, obj):\n        raise NotImplementedError\n\n    def _search(self, queryset, query_string, fields=None):\n        raise NotImplementedError\n\n    def search(self, query_string, model_or_queryset, fields=None, filters=None, prefetch_related=None):\n        # Find model/queryset\n        if isinstance(model_or_queryset, QuerySet):\n            model = model_or_queryset.model\n            queryset = model_or_queryset\n        else:\n            model = model_or_queryset\n            queryset = model_or_queryset.objects.all()\n\n        # Model must be a class that is in the index\n        if not class_is_indexed(model):\n            return []\n\n        # Check that theres still a query string after the clean up\n        if query_string == \"\":\n            return []\n\n        # Apply filters to queryset\n        if filters:\n            queryset = queryset.filter(**filters)\n\n        # Prefetch related\n        if prefetch_related:\n            for prefetch in prefetch_related:\n                queryset = queryset.prefetch_related(prefetch)\n\n        # Search\n        return self._search(queryset, query_string, fields=fields)\n", "path": "wagtail/wagtailsearch/backends/base.py"}]}