Fix undefined-loop-variable with NoReturn and Never

pylint/checkers/variables.py

@@ -28,7 +28,12 @@
     in_type_checking_block,
     is_postponed_evaluation_enabled,
 )
-from pylint.constants import PY39_PLUS, TYPING_TYPE_CHECKS_GUARDS
+from pylint.constants import (
+    PY39_PLUS,
+    TYPING_NEVER,
+    TYPING_NORETURN,
+    TYPING_TYPE_CHECKS_GUARDS,
+)
 from pylint.interfaces import CONTROL_FLOW, HIGH, INFERENCE, INFERENCE_FAILURE
 from pylint.typing import MessageDefinitionTuple
 
@@ -2254,13 +2259,25 @@ def _loopvar_name(self, node: astroid.Name) -> None:
         if not isinstance(assign, nodes.For):
             self.add_message("undefined-loop-variable", args=node.name, node=node)
             return
-        if any(
-            isinstance(
+        for else_stmt in assign.orelse:
+            if isinstance(
                 else_stmt, (nodes.Return, nodes.Raise, nodes.Break, nodes.Continue)
-            )
-            for else_stmt in assign.orelse
-        ):
-            return
+            ):
+                return
+            # TODO: 2.16: Consider using RefactoringChecker._is_function_def_never_returning
+            if isinstance(else_stmt, nodes.Expr) and isinstance(
+                else_stmt.value, nodes.Call
+            ):
+                inferred_func = utils.safe_infer(else_stmt.value.func)
+                if (
+                    isinstance(inferred_func, nodes.FunctionDef)
+                    and inferred_func.returns
+                ):
+                    inferred_return = utils.safe_infer(inferred_func.returns)
+                    if isinstance(
+                        inferred_return, nodes.FunctionDef
+                    ) and inferred_return.qname() in {*TYPING_NORETURN, *TYPING_NEVER}:
+                        return
 
         maybe_walrus = utils.get_node_first_ancestor_of_type(node, nodes.NamedExpr)
         if maybe_walrus:

pylint/constants.py

@@ -155,3 +155,16 @@ def _get_pylint_home() -> str:
 
 
 PYLINT_HOME = _get_pylint_home()
+
+TYPING_NORETURN = frozenset(
+    (
+        "typing.NoReturn",
+        "typing_extensions.NoReturn",
+    )
+)
+TYPING_NEVER = frozenset(
+    (
+        "typing.Never",
+        "typing_extensions.Never",
+    )
+)

pylint/extensions/typing.py

@@ -17,6 +17,7 @@
     only_required_for_messages,
     safe_infer,
 )
+from pylint.constants import TYPING_NORETURN
 from pylint.interfaces import INFERENCE
 
 if TYPE_CHECKING:
@@ -75,12 +76,6 @@ class TypingAlias(NamedTuple):
 
 ALIAS_NAMES = frozenset(key.split(".")[1] for key in DEPRECATED_TYPING_ALIASES)
 UNION_NAMES = ("Optional", "Union")
-TYPING_NORETURN = frozenset(
-    (
-        "typing.NoReturn",
-        "typing_extensions.NoReturn",
-    )
-)
 
 
 class DeprecatedTypingAliasMsg(NamedTuple):

tests/functional/u/undefined/undefined_loop_variable.py

@@ -1,9 +1,12 @@
 # pylint: disable=missing-docstring,redefined-builtin, consider-using-f-string, unnecessary-direct-lambda-call
 
+from typing import NoReturn
+
+
 def do_stuff(some_random_list):
     for var in some_random_list:
         pass
-    return var # [undefined-loop-variable]
+    return var  # [undefined-loop-variable]
 
 
 def do_else(some_random_list):
@@ -14,15 +17,16 @@ def do_else(some_random_list):
         var = 84
     return var
 
-__revision__ = 'yo'
+
+__revision__ = "yo"
 
 TEST_LC = [C for C in __revision__ if C.isalpha()]
-B = [B for B in  __revision__ if B.isalpha()]
-VAR2 = B # nor this one
+B = [B for B in __revision__ if B.isalpha()]
+VAR2 = B  # nor this one
 
 for var1, var2 in TEST_LC:
     var1 = var2 + 4
-VAR3 = var1 # [undefined-loop-variable]
+VAR3 = var1  # [undefined-loop-variable]
 
 for note in __revision__:
     note.something()
@@ -70,9 +74,10 @@ def do_stuff_with_a_range():
 def do_stuff_with_redefined_range():
     def range(key):
         yield from [1, key]
+
     for var in range(3):
         pass
-    return var # [undefined-loop-variable]
+    return var  # [undefined-loop-variable]
 
 
 def test(content):
@@ -81,13 +86,13 @@ def handle_line(layne):
         if "X" in layne:
             layne = layne.replace("X", "Y")
         elif "Y" in layne:  # line 5
-            layne = '{}'.format(layne)
+            layne = "{}".format(layne)
         elif "Z" in layne:  # line 7
-            layne = f'{layne}'
+            layne = f"{layne}"
         else:
-            layne = '%s' % layne  # line 10
+            layne = "%s" % layne  # line 10
 
-    for layne in content.split('\n'):
+    for layne in content.split("\n"):
         handle_line(layne)
 
 
@@ -125,25 +130,33 @@ def for_else_continue(iterable):
         print(thing)
 
 
+def for_else_no_return(iterable):
+    def fail() -> NoReturn:
+        ...
+
+    while True:
+        for thing in iterable:
+            break
+        else:
+            fail()
+        print(thing)
+
+
 lst = []
 lst2 = [1, 2, 3]
 
 for item in lst:
     pass
 
-bigger = [
-    [
-        x for x in lst2 if x > item
-    ]
-    for item in lst
-]
+bigger = [[x for x in lst2 if x > item] for item in lst]
 
 
 def lambda_in_first_of_two_loops():
     """https://github.com/PyCQA/pylint/issues/6419"""
     my_list = []
     for thing in my_list:
-        print_it = lambda: print(thing)  # pylint: disable=cell-var-from-loop, unnecessary-lambda-assignment
+        # pylint: disable-next=cell-var-from-loop, unnecessary-lambda-assignment
+        print_it = lambda: print(thing)
         print_it()
 
     for thing in my_list:

tests/functional/u/undefined/undefined_loop_variable.txt

@@ -1,4 +1,4 @@
-undefined-loop-variable:6:11:6:14:do_stuff:Using possibly undefined loop variable 'var':UNDEFINED
-undefined-loop-variable:25:7:25:11::Using possibly undefined loop variable 'var1':UNDEFINED
-undefined-loop-variable:75:11:75:14:do_stuff_with_redefined_range:Using possibly undefined loop variable 'var':UNDEFINED
-undefined-loop-variable:181:11:181:20:find_even_number:Using possibly undefined loop variable 'something':UNDEFINED
+undefined-loop-variable:9:11:9:14:do_stuff:Using possibly undefined loop variable 'var':UNDEFINED
+undefined-loop-variable:29:7:29:11::Using possibly undefined loop variable 'var1':UNDEFINED
+undefined-loop-variable:80:11:80:14:do_stuff_with_redefined_range:Using possibly undefined loop variable 'var':UNDEFINED
+undefined-loop-variable:194:11:194:20:find_even_number:Using possibly undefined loop variable 'something':UNDEFINED

tests/functional/u/undefined/undefined_loop_variable_py311.py

@@ -0,0 +1,17 @@
+"""Tests for undefined-loop-variable using Python 3.11 syntax."""
+
+from typing import Never
+
+
+def for_else_never(iterable):
+    """Test for-else with Never type."""
+
+    def idontreturn() -> Never:
+        """This function never returns."""
+
+    while True:
+        for thing in iterable:
+            break
+        else:
+            idontreturn()
+        print(thing)

tests/functional/u/undefined/undefined_loop_variable_py311.rc

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