invocation-scoped fixtures show up once with --fixtures

_pytest/python.py

@@ -1014,16 +1014,26 @@ def _showfixtures_main(config, session):
     fm = session._fixturemanager
 
     available = []
+    seen = set()
+
     for argname, fixturedefs in fm._arg2fixturedefs.items():
         assert fixturedefs is not None
         if not fixturedefs:
             continue
         for fixturedef in fixturedefs:
             loc = getlocation(fixturedef.func, curdir)
+            fixture_argname = fixturedef.argname
+            # invocation-scoped fixtures have argname in the form
+            # "<name>:<scope>" (for example: "monkeypatch:session").
+            if ':' in fixture_argname:
+                fixture_argname = fixture_argname.split(':')[0]
+            if (fixture_argname, loc) in seen:
+                continue
+            seen.add((fixture_argname, loc))
             available.append((len(fixturedef.baseid),
                               fixturedef.func.__module__,
                               curdir.bestrelpath(loc),
-                              fixturedef.argname, fixturedef))
+                              fixture_argname, fixturedef))
 
     available.sort()
     currentmodule = None

testing/python/fixture.py

@@ -2725,6 +2725,13 @@ class TestShowFixtures:
                 Hi from test module
         ''')
 
+    def test_show_invocation_fixtures(self, testdir):
+        """py.test --fixtures should display invocation-scoped fixtures once.
+        """
+        result = testdir.runpytest("--fixtures")
+        result.stdout.fnmatch_lines('''monkeypatch''')
+        assert 'monkeypatch:session' not in result.stdout.str()
+
 
 @pytest.mark.parametrize('flavor', ['fixture', 'yield_fixture'])
 class TestContextManagerFixtureFuncs: