Fix Arguments.arguments so it actually returns all arguments

Closes #2213.

Arguments.arguments() has been modified so that it returns all arguments
as it should (according to its own doc). A test case was also added to
verify this.

Author: crazybolillo

astroid/nodes/node_classes.py

@@ -780,7 +780,21 @@ def fromlineno(self) -> int:
     @cached_property
     def arguments(self):
         """Get all the arguments for this node, including positional only and positional and keyword"""
-        return list(itertools.chain((self.posonlyargs or ()), self.args or ()))
+        retval = list(
+            itertools.chain(
+                (self.posonlyargs or ()), (self.args or ()), (self.kwonlyargs or ())
+            )
+        )
+        if self.vararg:
+            retval.append(
+                Name(self.vararg, -1, -1, self, end_lineno=None, end_col_offset=None)
+            )
+        if self.kwarg:
+            retval.append(
+                Name(self.kwarg, -1, -1, self, end_lineno=None, end_col_offset=None)
+            )
+
+        return retval
 
     def format_args(self, *, skippable_names: set[str] | None = None) -> str:
         """Get the arguments formatted as string.

tests/test_nodes.py

@@ -22,6 +22,7 @@
     Uninferable,
     bases,
     builder,
+    extract_node,
     nodes,
     parse,
     test_utils,
@@ -1943,3 +1944,28 @@ def test_str_repr_no_warnings(node):
     test_node = node(**args)
     str(test_node)
     repr(test_node)
+
+
+def test_arguments_contains_all():
+    """Ensure Arguments.arguments actually returns all available arguments"""
+
+    def manually_get_args(arg_node) -> set:
+        names = set()
+        if arg_node.args.vararg:
+            names.add(arg_node.args.vararg)
+        if arg_node.args.kwarg:
+            names.add(arg_node.args.kwarg)
+
+        names.update([x.name for x in arg_node.args.args])
+        names.update([x.name for x in arg_node.args.kwonlyargs])
+
+        return names
+
+    node = extract_node("""def a(fruit: str, *args, b=None, c=None, **kwargs): ...""")
+    assert manually_get_args(node) == {x.name for x in node.args.arguments}
+
+    node = extract_node("""def a(mango: int, b="banana", c=None, **kwargs): ...""")
+    assert manually_get_args(node) == {x.name for x in node.args.arguments}
+
+    node = extract_node("""def a(self, num = 10, *args): ...""")
+    assert manually_get_args(node) == {x.name for x in node.args.arguments}