Generic sitemap (#1198)

* Add test for both issue cases

* Use generic type and add new django 4.1 `get_latest_lastmod` method

* Add Sitemap to monkeypatch

* Update test case to use generic + add failing case

* Test GenericSitemap too

tests/typecheck/contrib/sitemaps/test_generic_sitemap.yml

@@ -0,0 +1,80 @@
+-   case: test_items_custom_model
+    main: |
+        from django.contrib.sitemaps import GenericSitemap, Sitemap
+        from django.contrib.sitemaps.views import sitemap
+        from django.db.models import QuerySet
+        from django.urls import path, reverse
+        from myapp.models import Offer
+
+        class OfferSitemap(Sitemap[Offer]):
+            priority = 1
+            changefreq = "always"
+
+            def items(self) -> QuerySet[Offer]:
+                return Offer.objects.all()
+
+            def location(self, item: Offer) -> str:
+                return reverse(
+                    "myapp:detail-offer",
+                    kwargs={
+                        "provider_name": item.provider,
+                        "offer_name": item.trc, # E: "Offer" has no attribute "trc"
+                    },
+                )
+
+        class WrongOfferSitemap(Sitemap[Offer]):
+            def items(self) -> str:
+                return "Yes"
+            def location(self, item: str) -> int:
+                return 1
+
+        info_dict = {"queryset": Offer.objects.all()}
+        broken_info_dict = {"queryset": [1, 2]}
+
+        urlpatterns = [
+            path(
+                'sitemap.xml', sitemap,
+                {'sitemaps': {'offers': GenericSitemap[Offer](info_dict, priority=0.6)}},
+                name='django.contrib.sitemaps.views.sitemap'
+            ),
+            path(
+                'broken_sitemap.xml', sitemap,
+                {'sitemaps': {'offers': GenericSitemap[Offer](broken_info_dict, priority=0.6)}},
+                name='django.contrib.sitemaps.views.broken_sitemap'
+            ),
+        ]
+    out: |
+        main:24: error: Return type "str" of "items" incompatible with return type "Iterable[Offer]" in supertype "Sitemap"
+        main:26: error: Argument 1 of "location" is incompatible with supertype "Sitemap"; supertype defines the argument type as "Offer"
+        main:26: note: This violates the Liskov substitution principle
+        main:26: note: See https://mypy.readthedocs.io/en/stable/common_issues.html#incompatible-overrides
+        main:26: error: Return type "int" of "location" incompatible with return type "str" in supertype "Sitemap"
+        main:40: error: Argument 1 to "GenericSitemap" has incompatible type "Dict[str, List[int]]"; expected "Mapping[str, Union[datetime, _QuerySet[Offer, Offer], str]]"
+
+    installed_apps:
+        - myapp
+    files:
+        -   path: myapp/__init__.py
+        -   path: myapp/models.py
+            content: |
+                from django.db import models
+
+                class Offer(models.Model):
+                    provider = models.ForeignKey("self", on_delete=models.CASCADE)
+                    url_name = models.CharField()
+
+-   case: test_items_string_sequence
+    main: |
+        from django.contrib.sitemaps import Sitemap
+        from typing import List
+        from django.urls import reverse
+
+        class StaticViewSitemap(Sitemap[str]):
+            priority = 1
+            changefreq = "always"
+
+            def items(self) -> List[str]:
+                return ["home", "about", "contact", "recommendations", "privacy-policy", "blog"]
+
+            def location(self, item: str) -> str:
+                return reverse(item)