py36+: remove _pytest.compat.order_preserving_dict

src/_pytest/cacheprovider.py

@@ -22,7 +22,6 @@ from .reports import CollectReport
 from _pytest import nodes
 from _pytest._io import TerminalWriter
 from _pytest.compat import final
-from _pytest.compat import order_preserving_dict
 from _pytest.config import Config
 from _pytest.config import ExitCode
 from _pytest.config.argparsing import Parser
@@ -367,8 +366,8 @@ class NFPlugin:
         yield
 
         if self.active:
-            new_items: Dict[str, nodes.Item] = order_preserving_dict()
-            other_items: Dict[str, nodes.Item] = order_preserving_dict()
+            new_items: Dict[str, nodes.Item] = {}
+            other_items: Dict[str, nodes.Item] = {}
             for item in items:
                 if item.nodeid not in self.cached_nodeids:
                     new_items[item.nodeid] = item

src/_pytest/compat.py

@@ -366,18 +366,6 @@ else:
             return value
 
 
-# Sometimes an algorithm needs a dict which yields items in the order in which
-# they were inserted when iterated. Since Python 3.7, `dict` preserves
-# insertion order. Since `dict` is faster and uses less memory than
-# `OrderedDict`, prefer to use it if possible.
-if sys.version_info >= (3, 7):
-    order_preserving_dict = dict
-else:
-    from collections import OrderedDict
-
-    order_preserving_dict = OrderedDict
-
-
 # Perform exhaustiveness checking.
 #
 # Consider this example:

src/_pytest/fixtures.py

@@ -45,7 +45,6 @@ from _pytest.compat import getimfunc
 from _pytest.compat import getlocation
 from _pytest.compat import is_generator
 from _pytest.compat import NOTSET
-from _pytest.compat import order_preserving_dict
 from _pytest.compat import safe_getattr
 from _pytest.config import _PluggyPlugin
 from _pytest.config import Config
@@ -276,21 +275,12 @@ def reorder_items(items: Sequence[nodes.Item]) -> List[nodes.Item]:
         item_d: Dict[_Key, Deque[nodes.Item]] = defaultdict(deque)
         items_by_argkey[scopenum] = item_d
         for item in items:
-            # cast is a workaround for https://github.com/python/typeshed/issues/3800.
-            keys = cast(
-                "Dict[_Key, None]",
-                order_preserving_dict.fromkeys(
-                    get_parametrized_fixture_keys(item, scopenum), None
-                ),
-            )
+            keys = dict.fromkeys(get_parametrized_fixture_keys(item, scopenum), None)
             if keys:
                 d[item] = keys
                 for key in keys:
                     item_d[key].append(item)
-    # cast is a workaround for https://github.com/python/typeshed/issues/3800.
-    items_dict = cast(
-        Dict[nodes.Item, None], order_preserving_dict.fromkeys(items, None)
-    )
+    items_dict = dict.fromkeys(items, None)
     return list(reorder_items_atscope(items_dict, argkeys_cache, items_by_argkey, 0))
 
 
@@ -314,17 +304,17 @@ def reorder_items_atscope(
         return items
     ignore: Set[Optional[_Key]] = set()
     items_deque = deque(items)
-    items_done: Dict[nodes.Item, None] = order_preserving_dict()
+    items_done: Dict[nodes.Item, None] = {}
     scoped_items_by_argkey = items_by_argkey[scopenum]
     scoped_argkeys_cache = argkeys_cache[scopenum]
     while items_deque:
-        no_argkey_group: Dict[nodes.Item, None] = order_preserving_dict()
+        no_argkey_group: Dict[nodes.Item, None] = {}
         slicing_argkey = None
         while items_deque:
             item = items_deque.popleft()
             if item in items_done or item in no_argkey_group:
                 continue
-            argkeys = order_preserving_dict.fromkeys(
+            argkeys = dict.fromkeys(
                 (k for k in scoped_argkeys_cache.get(item, []) if k not in ignore), None
             )
             if not argkeys:

src/_pytest/terminal.py

@@ -35,7 +35,6 @@ from _pytest._code import ExceptionInfo
 from _pytest._code.code import ExceptionRepr
 from _pytest._io.wcwidth import wcswidth
 from _pytest.compat import final
-from _pytest.compat import order_preserving_dict
 from _pytest.config import _PluggyPlugin
 from _pytest.config import Config
 from _pytest.config import ExitCode
@@ -909,9 +908,7 @@ class TerminalReporter:
             if not warning_reports:
                 return
 
-            reports_grouped_by_message: Dict[str, List[WarningReport]] = (
-                order_preserving_dict()
-            )
+            reports_grouped_by_message: Dict[str, List[WarningReport]] = {}
             for wr in warning_reports:
                 reports_grouped_by_message.setdefault(wr.message, []).append(wr)
 
@@ -925,7 +922,7 @@ class TerminalReporter:
                 if len(locations) < 10:
                     return "\n".join(map(str, locations))
 
-                counts_by_filename: Dict[str, int] = order_preserving_dict()
+                counts_by_filename: Dict[str, int] = {}
                 for loc in locations:
                     key = str(loc).split("::", 1)[0]
                     counts_by_filename[key] = counts_by_filename.get(key, 0) + 1