Fix startup crash on Python 3.10.0 caused by missing NodeId cache

AUTHORS

@@ -4,6 +4,7 @@ merlinux GmbH, Germany, office at merlinux eu
 Contributors include::
 
 Aaron Coleman
+Aathithya Arasu S
 Abdeali JK
 Abdelrahman Elbehery
 Abhijeet Kasurde

changelog/15337.bugfix.rst

@@ -0,0 +1 @@
+Fixed an ``INTERNALERROR`` crash when running pytest on Python 3.10.0 exactly: a slotted dataclass field was never initialized on that interpreter version (:issue:`15337`).

src/_pytest/nodeid.py

@@ -57,8 +57,13 @@ def parse(cls, nodeid: str) -> NodeId:
         return self
 
     def __str__(self) -> str:
-        if self._str_cache is not None:
-            return self._str_cache
+        # Read ``_str_cache`` defensively: on Python 3.10.0, slotted dataclass
+        # fields with ``init=False`` and a default value are never set
+        # (https://github.com/python/cpython/issues/88815), so the attribute
+        # may be missing entirely.
+        cache: str | None = getattr(self, "_str_cache", None)
+        if cache is not None:
+            return cache
         s = "::".join((self.path, *self.names))
         if self.params is not None:
             s += f"[{self.params}]"

testing/test_nodeid.py

@@ -23,6 +23,19 @@ def test_str_with_params(self) -> None:
         node_id = NodeId(path="a/test_b.py", names=("test_c",), params="1-x")
         assert str(node_id) == "a/test_b.py::test_c[1-x]"
 
+    def test_str_missing_str_cache(self) -> None:
+        # Simulate Python 3.10.0 (https://github.com/python/cpython/issues/88815):
+        # slotted dataclass fields with init=False and a default are never set,
+        # so _str_cache may be missing entirely (gh-15337).
+        node_id = NodeId(path="a/test_b.py", names=("test_c",))
+        # Ensure the attribute exists first so the deletion works on every
+        # interpreter version (on 3.10.0 it is never set in the first place).
+        object.__setattr__(node_id, "_str_cache", None)
+        object.__delattr__(node_id, "_str_cache")
+        assert str(node_id) == "a/test_b.py::test_c"
+        # The cache must be repopulated by the first __str__ call.
+        assert node_id._str_cache == "a/test_b.py::test_c"
+
     # -- child() and leaf() --
 
     def test_child(self) -> None: