From a267a622eb5af73f71f7bdf71ef83ed2ed27b782 Mon Sep 17 00:00:00 2001
From: Ran Benita <ran@unusedvar.com>
Date: Tue, 25 Aug 2020 21:51:08 +0300
Subject: [PATCH] python: fix empty parametrize() leading to "NotSetType.token"
 id

In ff8b7884e8f1019f60f270eab2c4909ff557dd4e NOTSET was changed to a
singleton enum, which ended up unexpectedly triggering a code path in ID
generation which checks for `isinstance(Enum)`.

Add an explicit case for it, which is not too bad anyway.
---
 changelog/7686.bugfix.rst  | 2 ++
 src/_pytest/python.py      | 3 +++
 testing/python/metafunc.py | 9 +++++++++
 3 files changed, 14 insertions(+)
 create mode 100644 changelog/7686.bugfix.rst

diff --git a/changelog/7686.bugfix.rst b/changelog/7686.bugfix.rst
new file mode 100644
index 000000000..8549fae8e
--- /dev/null
+++ b/changelog/7686.bugfix.rst
@@ -0,0 +1,2 @@
+Fixed `NotSetType.token` being used as the parameter ID when the parametrization list is empty.
+Regressed in pytest 6.0.0.
diff --git a/src/_pytest/python.py b/src/_pytest/python.py
index f792acbd8..21aa84576 100644
--- a/src/_pytest/python.py
+++ b/src/_pytest/python.py
@@ -1293,6 +1293,9 @@ def _idval(
         return str(val)
     elif isinstance(val, REGEX_TYPE):
         return ascii_escaped(val.pattern)
+    elif val is NOTSET:
+        # Fallback to default. Note that NOTSET is an enum.Enum.
+        pass
     elif isinstance(val, enum.Enum):
         return str(val)
     elif isinstance(getattr(val, "__name__", None), str):
diff --git a/testing/python/metafunc.py b/testing/python/metafunc.py
index 7aa608a04..6b5910456 100644
--- a/testing/python/metafunc.py
+++ b/testing/python/metafunc.py
@@ -21,6 +21,7 @@ from _pytest import fixtures
 from _pytest import python
 from _pytest.compat import _format_args
 from _pytest.compat import getfuncargnames
+from _pytest.compat import NOTSET
 from _pytest.outcomes import fail
 from _pytest.pytester import Testdir
 from _pytest.python import _idval
@@ -359,6 +360,14 @@ class TestMetafunc:
         for val, expected in values:
             assert _idval(val, "a", 6, None, nodeid=None, config=None) == expected
 
+    def test_notset_idval(self) -> None:
+        """Test that a NOTSET value (used by an empty parameterset) generates
+        a proper ID.
+
+        Regression test for #7686.
+        """
+        assert _idval(NOTSET, "a", 0, None, nodeid=None, config=None) == "a0"
+
     def test_idmaker_autoname(self) -> None:
         """#250"""
         result = idmaker(