[Backport maintenance/3.3.x] Fix IndexError when typing._alias() has missing arguments (#2624)

* Fix IndexError when typing._alias() has missing arguments Closes #2513 (cherry picked from commit ca0230d) Co-authored-by: correctmost <134317971+correctmost@users.noreply.github.com> Co-authored-by: Pierre Sassoulas <pierre.sassoulas@gmail.com>

Author: 3 people

ChangeLog

@@ -13,6 +13,10 @@ What's New in astroid 3.3.6?
 ============================
 Release date: TBA
 
+* Fix crash when typing._alias() call is missing arguments.
+
+ Closes #2513
+
 
 
 What's New in astroid 3.3.5?

astroid/brain/brain_typing.py

@@ -257,6 +257,7 @@ def _looks_like_typing_alias(node: Call) -> bool:
  isinstance(node.func, Name)
  # TODO: remove _DeprecatedGenericAlias when Py3.14 min
  and node.func.name in {"_alias", "_DeprecatedGenericAlias"}
+ and len(node.args) == 2
  and (
  # _alias function works also for builtins object such as list and dict
  isinstance(node.args[0], (Attribute, Name))

tests/brain/test_typing.py

@@ -4,7 +4,7 @@
 
 import pytest
 
-from astroid import builder
+from astroid import bases, builder, nodes
 from astroid.exceptions import InferenceError
 
 
@@ -23,3 +23,50 @@ def test_infer_typevar() -> None:
  )
  with pytest.raises(InferenceError):
  call_node.inferred()
+
+
+class TestTypingAlias:
+ def test_infer_typing_alias(self) -> None:
+ """
+ Test that _alias() calls can be inferred.
+ """
+ node = builder.extract_node(
+ """
+ from typing import _alias
+ x = _alias(int, float)
+ """
+ )
+ assert isinstance(node, nodes.Assign)
+ assert isinstance(node.value, nodes.Call)
+ inferred = next(node.value.infer())
+ assert isinstance(inferred, nodes.ClassDef)
+ assert len(inferred.bases) == 1
+ assert inferred.bases[0].name == "int"
+
+ @pytest.mark.parametrize(
+ "alias_args",
+ [
+ "", # two missing arguments
+ "int", # one missing argument
+ "int, float, tuple", # one additional argument
+ ],
+ )
+ def test_infer_typing_alias_incorrect_number_of_arguments(
+ self, alias_args: str
+ ) -> None:
+ """
+ Regression test for: https://github.com/pylint-dev/astroid/issues/2513
+
+ Test that _alias() calls with the incorrect number of arguments can be inferred.
+ """
+ node = builder.extract_node(
+ f"""
+ from typing import _alias
+ x = _alias({alias_args})
+ """
+ )
+ assert isinstance(node, nodes.Assign)
+ assert isinstance(node.value, nodes.Call)
+ inferred = next(node.value.infer())
+ assert isinstance(inferred, bases.Instance)
+ assert inferred.name == "_SpecialGenericAlias"