Fix crash for unneccessary-ellipsis checker (#6038)

When an ellipsis is used inside of a list or inside a container

Closes #6037

Co-authored-by: Mark Byrne <mark.byrne@rabobank.com>
Co-authored-by: Pierre Sassoulas <pierre.sassoulas@gmail.com>

ChangeLog

@@ -24,6 +24,12 @@ Release date: TBA
 
   Closes #6028
 
+* Fix crash for ``unneccessary-ellipsis`` checker when an ellipsis is used inside of a container.
+
+  Closes #6037
+  Closes #6048
+
+
 What's New in Pylint 2.13.3?
 ============================
 Release date: 2022-03-29

pylint/checkers/ellipsis_checker.py

@@ -43,7 +43,13 @@ def visit_const(self, node: nodes.Const) -> None:
             node.pytype() == "builtins.Ellipsis"
             and not isinstance(
                 node.parent,
-                (nodes.Assign, nodes.AnnAssign, nodes.Call, nodes.Arguments),
+                (
+                    nodes.AnnAssign,
+                    nodes.Arguments,
+                    nodes.Assign,
+                    nodes.BaseContainer,
+                    nodes.Call,
+                ),
             )
             and (
                 len(node.parent.parent.child_sequence(node.parent)) > 1

tests/functional/u/unnecessary/unnecessary_ellipsis.py

@@ -101,3 +101,14 @@ def __getitem__(self, index: Union[int, slice]) -> Union[int, List[int]]:
 # Ellipsis is allowed as a default argument
 def func_with_ellipsis_default_arg(a = ...) -> None:
     "Some docstring."
+
+
+# Ignore if the ellipsis is inside a container:
+my_list = [...]
+my_tuple = (...,)
+my_set = {...}
+
+# Ellipsis inside a container which is a value in a dictionary
+mydict1 = {'x': [...]}
+mydict2 = {'x': {...}}
+mydict3 = {'x': (...,)}