Fix FP for possibly-used-before-assignment with assert_never() (#…

…9645)

doc/whatsnew/fragments/9643.false_positive

@@ -0,0 +1,4 @@
+Fix a false positive for `possibly-used-before-assignment` when using
+`typing.assert_never()` (3.11+) to indicate exhaustiveness.
+
+Closes #9643

pylint/checkers/variables.py

@@ -32,7 +32,7 @@
     is_sys_guard,
     overridden_method,
 )
-from pylint.constants import PY39_PLUS, TYPING_NEVER, TYPING_NORETURN
+from pylint.constants import PY39_PLUS, PY311_PLUS, TYPING_NEVER, TYPING_NORETURN
 from pylint.interfaces import CONTROL_FLOW, HIGH, INFERENCE, INFERENCE_FAILURE
 from pylint.typing import MessageDefinitionTuple
 
@@ -940,12 +940,15 @@ def _uncertain_nodes_in_except_blocks(
     def _defines_name_raises_or_returns(name: str, node: nodes.NodeNG) -> bool:
         if isinstance(node, (nodes.Raise, nodes.Assert, nodes.Return, nodes.Continue)):
             return True
-        if (
-            isinstance(node, nodes.Expr)
-            and isinstance(node.value, nodes.Call)
-            and utils.is_terminating_func(node.value)
-        ):
-            return True
+        if isinstance(node, nodes.Expr) and isinstance(node.value, nodes.Call):
+            if utils.is_terminating_func(node.value):
+                return True
+            if (
+                PY311_PLUS
+                and isinstance(node.value.func, nodes.Name)
+                and node.value.func.name == "assert_never"
+            ):
+                return True
         if (
             isinstance(node, nodes.AnnAssign)
             and node.value

pylint/constants.py

@@ -17,6 +17,7 @@
 PY38_PLUS = sys.version_info[:2] >= (3, 8)
 PY39_PLUS = sys.version_info[:2] >= (3, 9)
 PY310_PLUS = sys.version_info[:2] >= (3, 10)
+PY311_PLUS = sys.version_info[:2] >= (3, 11)
 PY312_PLUS = sys.version_info[:2] >= (3, 12)
 
 IS_PYPY = platform.python_implementation() == "PyPy"

tests/functional/u/used/used_before_assignment_py311.py

@@ -0,0 +1,21 @@
+"""assert_never() introduced in 3.11"""
+from enum import Enum
+from typing import assert_never
+
+
+class MyEnum(Enum):
+    """A lovely enum."""
+    VAL1 = 1
+    VAL2 = 2
+
+
+def do_thing(val: MyEnum) -> None:
+    """Do a thing."""
+    if val is MyEnum.VAL1:
+        note = 'got 1'
+    elif val is MyEnum.VAL2:
+        note = 'got 2'
+    else:
+        assert_never(val)
+
+    print('Note:', note)

tests/functional/u/used/used_before_assignment_py311.rc

@@ -0,0 +1,2 @@
+[testoptions]
+min_pyver=3.11