avoid using __file__ in pytest_plugin_registered as can be wrong on Windows

.pre-commit-config.yaml

@@ -64,6 +64,7 @@ repos:
         additional_dependencies:
           - iniconfig>=1.1.0
           - attrs>=19.2.0
+          - pluggy
           - packaging
           - tomli
           - types-pkg_resources

changelog/11825.improvement.rst

@@ -0,0 +1 @@
+The :hook:`pytest_plugin_registered` hook has a new ``plugin_name`` parameter containing the name by which ``plugin`` is registered.

src/_pytest/config/__init__.py

@@ -490,15 +490,19 @@ def register(
                 )
             )
             return None
-        ret: Optional[str] = super().register(plugin, name)
-        if ret:
+        plugin_name = super().register(plugin, name)
+        if plugin_name is not None:
             self.hook.pytest_plugin_registered.call_historic(
-                kwargs=dict(plugin=plugin, manager=self)
+                kwargs=dict(
+                    plugin=plugin,
+                    plugin_name=plugin_name,
+                    manager=self,
+                )
             )
 
             if isinstance(plugin, types.ModuleType):
                 self.consider_module(plugin)
-        return ret
+        return plugin_name
 
     def getplugin(self, name: str):
         # Support deprecated naming because plugins (xdist e.g.) use it.

src/_pytest/fixtures.py

@@ -1483,25 +1483,27 @@
 
         return FuncFixtureInfo(argnames, initialnames, names_closure, arg2fixturedefs)
 
-    def pytest_plugin_registered(self, plugin: _PluggyPlugin) -> None:
-        nodeid = None
-        try:
-            p = absolutepath(plugin.__file__)  # type: ignore[attr-defined]
-        except AttributeError:
-            pass
+    def pytest_plugin_registered(self, plugin: _PluggyPlugin, plugin_name: str) -> None:
+        # Fixtures defined in conftest plugins are only visible to within the
+        # conftest's directory. This is unlike fixtures in non-conftest plugins
+        # which have global visibility. So for conftests, construct the base
+        # nodeid from the plugin name (which is the conftest path).
+        if plugin_name and plugin_name.endswith("conftest.py"):
+            # Note: we explicitly do *not* use `plugin.__file__` here -- The
+            # difference is that plugin_name has the correct capitalization on
+            # case-insensitive systems (Windows) and other normalization issues
+            # (issue #11816).
+            conftestpath = absolutepath(plugin_name)
+            try:
+                nodeid = str(conftestpath.parent.relative_to(self.config.rootpath))
+            except ValueError:
+                nodeid = ""
+            if nodeid == ".":
+                nodeid = ""
+            if os.sep != nodes.SEP:
+                nodeid = nodeid.replace(os.sep, nodes.SEP)
         else:
-            # Construct the base nodeid which is later used to check
-            # what fixtures are visible for particular tests (as denoted
-            # by their test id).
-            if p.name == "conftest.py":
-                try:
-                    nodeid = str(p.parent.relative_to(self.config.rootpath))
-                except ValueError:
-                    nodeid = ""
-                if nodeid == ".":
-                    nodeid = ""
-                if os.sep != nodes.SEP:
-                    nodeid = nodeid.replace(os.sep, nodes.SEP)
+            nodeid = None
 
         self.parsefactories(plugin, nodeid)
 

src/_pytest/hookspec.py

@@ -63,12 +63,15 @@ def pytest_addhooks(pluginmanager: "PytestPluginManager") -> None:
 
 @hookspec(historic=True)
 def pytest_plugin_registered(
-    plugin: "_PluggyPlugin", manager: "PytestPluginManager"
+    plugin: "_PluggyPlugin",
+    plugin_name: str,
+    manager: "PytestPluginManager",
 ) -> None:
     """A new pytest plugin got registered.
 
     :param plugin: The plugin module or instance.
-    :param manager: pytest plugin manager.
+    :param plugin_name: The name by which the plugin is registered.
+    :param manager: The pytest plugin manager.
 
     .. note::
         This hook is incompatible with hook wrappers.