Fix invalid type false positive

doc/whatsnew/fragments/8205.false_positive

@@ -0,0 +1,3 @@
+Fix false positive for isinstance-second-argument-not-valid-type with union types.
+
+Closes #8205

pylint/checkers/typecheck.py

@@ -48,6 +48,7 @@
     supports_membership_test,
     supports_setitem,
 )
+from pylint.constants import PY310_PLUS
 from pylint.interfaces import HIGH, INFERENCE
 from pylint.typing import MessageDefinitionTuple
 
@@ -796,6 +797,10 @@ def _is_c_extension(module_node: InferenceResult) -> bool:
 
 def _is_invalid_isinstance_type(arg: nodes.NodeNG) -> bool:
     # Return True if we are sure that arg is not a type
+    if PY310_PLUS and isinstance(arg, nodes.BinOp) and arg.op == "|":
+        return _is_invalid_isinstance_type(arg.left) or _is_invalid_isinstance_type(
+            arg.right
+        )
     inferred = utils.safe_infer(arg)
     if not inferred:
         # Cannot infer it so skip it.
@@ -806,6 +811,10 @@ def _is_invalid_isinstance_type(arg: nodes.NodeNG) -> bool:
         return False
     if isinstance(inferred, astroid.Instance) and inferred.qname() == BUILTIN_TUPLE:
         return False
+    if PY310_PLUS and isinstance(inferred, bases.UnionType):
+        return _is_invalid_isinstance_type(
+            inferred.left
+        ) or _is_invalid_isinstance_type(inferred.right)
     return True
 
 

pylint/constants.py

@@ -18,6 +18,7 @@
 
 PY38_PLUS = sys.version_info[:2] >= (3, 8)
 PY39_PLUS = sys.version_info[:2] >= (3, 9)
+PY310_PLUS = sys.version_info[:2] >= (3, 10)
 
 IS_PYPY = platform.python_implementation() == "PyPy"
 

tests/functional/ext/typing/redundant_typehint_argument.py

@@ -1,4 +1,4 @@
-""""Checks for redundant Union typehints in assignments"""
+"""Checks for redundant Union typehints in assignments"""
 # pylint: disable=deprecated-typing-alias,consider-alternative-union-syntax,consider-using-alias,invalid-name,unused-argument,missing-function-docstring
 
 from __future__ import annotations

tests/functional/ext/typing/redundant_typehint_argument_py310.py

@@ -1,4 +1,4 @@
-""""Checks for redundant Union typehints in assignments"""
+"""Checks for redundant Union typehints in assignments"""
 # pylint: disable=deprecated-typing-alias,consider-alternative-union-syntax,consider-using-alias,invalid-name,unused-argument,missing-function-docstring
 
 from __future__ import annotations

tests/functional/i/isinstance_second_argument_py310.py

@@ -0,0 +1,27 @@
+'''Tests for invalid isinstance with compound types'''
+
+# True negatives
+isinstance(0, int | str)
+isinstance(0, int | int | int)
+isinstance(0, int | str | list | float)
+isinstance(0, (int | str) | (list | float))
+
+IntOrStr = int | str
+isinstance(0, IntOrStr)
+ListOrDict = list | dict
+isinstance(0, (float | ListOrDict) | IntOrStr)
+
+# True positives
+isinstance(0, int | 5)  # [isinstance-second-argument-not-valid-type]
+isinstance(0, str | 5 | int)  # [isinstance-second-argument-not-valid-type]
+INT = 5
+isinstance(0, INT | int)  # [isinstance-second-argument-not-valid-type]
+
+
+# FALSE NEGATIVES
+
+# Parameterized generics will raise type errors at runtime.
+# Warnings should be raised, but aren't (yet).
+isinstance(0, list[int])
+ListOfInts = list[int]
+isinstance(0, ListOfInts)

tests/functional/i/isinstance_second_argument_py310.rc

@@ -0,0 +1,2 @@
+[testoptions]
+min_pyver=3.10

tests/functional/i/isinstance_second_argument_py310.txt

@@ -0,0 +1,3 @@
+isinstance-second-argument-not-valid-type:15:0:15:22::Second argument of isinstance is not a type:UNDEFINED
+isinstance-second-argument-not-valid-type:16:0:16:28::Second argument of isinstance is not a type:UNDEFINED
+isinstance-second-argument-not-valid-type:18:0:18:24::Second argument of isinstance is not a type:UNDEFINED