Remove stale plugin distribution entries on unregister

changelog/763.bugfix.rst

@@ -0,0 +1,5 @@
+``PluginManager.unregister()`` now removes the plugin from
+``list_plugin_distinfo()`` and ``list_plugin_distributions()``. Previously
+these kept reporting an unregistered plugin loaded via
+``load_setuptools_entrypoints()``, and re-registering it added a duplicate
+entry.

src/pluggy/_manager.py

@@ -320,6 +320,13 @@ def unregister(
         if self._name2plugin.get(name) is not None:
             del self._name2plugin[name]
 
+        # Drop any setuptools distribution bookkeeping for this plugin so it
+        # no longer shows up in list_plugin_distinfo()/list_plugin_distributions()
+        # and a later re-registration does not create duplicate entries.
+        self._plugin_distinfo[:] = [
+            (p, dist) for (p, dist) in self._plugin_distinfo if p is not plugin
+        ]
+
         return plugin
 
     def set_blocked(self, name: str) -> None:

testing/test_pluginmanager.py

@@ -959,6 +959,50 @@ def my_distributions():
     assert ret_distributions == [(plugin, dist)]
 
 
+def test_unregister_removes_plugin_distinfo(
+    monkeypatch: pytest.MonkeyPatch, pm: PluginManager
+) -> None:
+    """Unregistering a setuptools-loaded plugin clears its distinfo entries.
+
+    See https://github.com/pytest-dev/pluggy/issues/763.
+    """
+
+    class EntryPoint:
+        name = "myname"
+        group = "hello"
+        value = "myname:foo"
+
+        def load(self):
+            class PseudoPlugin:
+                pass
+
+            return PseudoPlugin()
+
+    class Distribution:
+        entry_points = (EntryPoint(),)
+
+    dist = cast(importlib.metadata.Distribution, Distribution())
+
+    monkeypatch.setattr(importlib.metadata, "distributions", lambda: (dist,))
+
+    assert pm.load_setuptools_entrypoints("hello") == 1
+    plugin = pm.get_plugin("myname")
+    assert plugin is not None
+    assert len(pm.list_plugin_distinfo()) == 1
+    assert len(pm.list_plugin_distributions()) == 1
+
+    # Unregistering must drop both distinfo views.
+    pm.unregister(name="myname")
+    assert pm.get_plugin("myname") is None
+    assert pm.list_plugin_distinfo() == []
+    assert pm.list_plugin_distributions() == []
+
+    # Re-registration must not leave duplicate distinfo entries behind.
+    assert pm.load_setuptools_entrypoints("hello") == 1
+    assert len(pm.list_plugin_distinfo()) == 1
+    assert len(pm.list_plugin_distributions()) == 1
+
+
 def test_add_tracefuncs(he_pm: PluginManager) -> None:
     out: list[Any] = []