python: small optimization in PyCollector.collect()

Inline `_makeitem()` so that `self.ihook` (which is moderately
expensive) can be called only once.

Note: the removed test "test_makeitem_non_underscore" comes from an old
behavior of skipping names that start with `_` which has since been
generalized, making the test no longer relevant.

src/_pytest/python.py

@@ -421,6 +421,7 @@ class PyCollector(PyobjMixin, nodes.Collector):
             dicts.append(basecls.__dict__)
         seen = set()  # type: Set[str]
         values = []  # type: List[Union[nodes.Item, nodes.Collector]]
+        ihook = self.ihook
         for dic in dicts:
             # Note: seems like the dict can change during iteration -
             # be careful not to remove the list() without consideration.
@@ -430,12 +431,15 @@ class PyCollector(PyobjMixin, nodes.Collector):
                 if name in seen:
                     continue
                 seen.add(name)
-                res = self._makeitem(name, obj)
+                res = ihook.pytest_pycollect_makeitem(
+                    collector=self, name=name, obj=obj
+                )
                 if res is None:
                     continue
-                if not isinstance(res, list):
-                    res = [res]
+                elif isinstance(res, list):
                     values.extend(res)
+                else:
+                    values.append(res)
 
         def sort_key(item):
             fspath, lineno, _ = item.reportinfo()
@@ -444,17 +448,6 @@ class PyCollector(PyobjMixin, nodes.Collector):
         values.sort(key=sort_key)
         return values
 
-    def _makeitem(
-        self, name: str, obj: object
-    ) -> Union[
-        None, nodes.Item, nodes.Collector, List[Union[nodes.Item, nodes.Collector]]
-    ]:
-        # assert self.ihook.fspath == self.fspath, self
-        item = self.ihook.pytest_pycollect_makeitem(
-            collector=self, name=name, obj=obj
-        )  # type: Union[None, nodes.Item, nodes.Collector, List[Union[nodes.Item, nodes.Collector]]]
-        return item
-
     def _genfunctions(self, name: str, funcobj) -> Iterator["Function"]:
         modulecol = self.getparent(Module)
         assert modulecol is not None

testing/python/collect.py

@@ -843,15 +843,6 @@ class TestConftestCustomization:
         result = testdir.runpytest("--collect-only")
         result.stdout.fnmatch_lines(["*MyFunction*some*"])
 
-    def test_makeitem_non_underscore(self, testdir, monkeypatch):
-        modcol = testdir.getmodulecol("def _hello(): pass")
-        values = []
-        monkeypatch.setattr(
-            pytest.Module, "_makeitem", lambda self, name, obj: values.append(name)
-        )
-        values = modcol.collect()
-        assert "_hello" not in values
-
     def test_issue2369_collect_module_fileext(self, testdir):
         """Ensure we can collect files with weird file extensions as Python
         modules (#2369)"""