Fix various issues regarding starred expressions

- Properly check for starred expression deletion
- Check for starred expressions not in tuple/list/set (when not in assignment)
- Fix a bug that considered starred expression assignment `[*x] = 1` as invalid
- Enhance test cases for valid and invalid `del` statements and starred expressions

parso/python/errors.py

@@ -147,6 +147,18 @@ def _remove_parens(atom):
     return atom
 
 
+def _skip_parens_bottom_up(node):
+    """
+    Returns an ancestor node of an expression, skipping all levels of parens
+    bottom-up.
+    """
+    while node.parent is not None:
+        node = node.parent
+        if node.type != 'atom' or node.children[0] != '(':
+            return node
+    return None
+
+
 def _iter_params(parent_node):
     return (n for n in parent_node.children if n.type == 'param')
 
@@ -730,51 +742,66 @@ class _FutureImportRule(SyntaxRule):
 @ErrorFinder.register_rule(type='star_expr')
 class _StarExprRule(SyntaxRule):
     message_iterable_unpacking = "iterable unpacking cannot be used in comprehension"
-    message_assignment = "can use starred expression only as assignment target"
 
     def is_issue(self, node):
+        def check_delete_starred(node):
+            while node.parent is not None:
+                node = node.parent
+                if node.type == 'del_stmt':
+                    return True
+                if node.type not in (*_STAR_EXPR_PARENTS, 'atom'):
+                    return False
+            return False
+
+        if check_delete_starred(node):
+            if self._normalizer.version >= (3, 9):
+                self.add_issue(node, message="cannot delete starred")
+            else:
+                self.add_issue(node, message="can't use starred expression here")
+            return
+
         if node.parent.type == 'testlist_comp':
             # [*[] for a in [1]]
             if node.parent.children[1].type in _COMP_FOR_TYPES:
                 self.add_issue(node, message=self.message_iterable_unpacking)
+                return
+
+        ancestor = _skip_parens_bottom_up(node)
+        # starred expression not in tuple/list/set
+        if ancestor.type not in (*_STAR_EXPR_PARENTS, 'dictorsetmaker', 'atom'):
+            self.add_issue(node, message="can't use starred expression here")
 
 
 @ErrorFinder.register_rule(types=_STAR_EXPR_PARENTS)
 class _StarExprParentRule(SyntaxRule):
     def is_issue(self, node):
-        if node.parent.type == 'del_stmt':
-            if self._normalizer.version >= (3, 9):
-                self.add_issue(node.parent, message="cannot delete starred")
-            else:
-                self.add_issue(node.parent, message="can't use starred expression here")
-        else:
-            def is_definition(node, ancestor):
-                if ancestor is None:
-                    return False
+        def is_definition(node, ancestor):
+            if ancestor is None:
+                return False
 
-                type_ = ancestor.type
-                if type_ == 'trailer':
-                    return False
+            type_ = ancestor.type
+            if type_ == 'trailer':
+                return False
 
-                if type_ == 'expr_stmt':
-                    return node.start_pos < ancestor.children[-1].start_pos
+            if type_ == 'expr_stmt':
+                return node.start_pos < ancestor.children[-1].start_pos
 
-                return is_definition(node, ancestor.parent)
+            return is_definition(node, ancestor.parent)
 
-            if is_definition(node, node.parent):
-                args = [c for c in node.children if c != ',']
-                starred = [c for c in args if c.type == 'star_expr']
-                if len(starred) > 1:
-                    if self._normalizer.version < (3, 9):
-                        message = "two starred expressions in assignment"
-                    else:
-                        message = "multiple starred expressions in assignment"
-                    self.add_issue(starred[1], message=message)
-                elif starred:
-                    count = args.index(starred[0])
-                    if count >= 256:
-                        message = "too many expressions in star-unpacking assignment"
-                        self.add_issue(starred[0], message=message)
+        if is_definition(node, node.parent):
+            args = [c for c in node.children if c != ',']
+            starred = [c for c in args if c.type == 'star_expr']
+            if len(starred) > 1:
+                if self._normalizer.version < (3, 9):
+                    message = "two starred expressions in assignment"
+                else:
+                    message = "multiple starred expressions in assignment"
+                self.add_issue(starred[1], message=message)
+            elif starred:
+                count = args.index(starred[0])
+                if count >= 256:
+                    message = "too many expressions in star-unpacking assignment"
+                    self.add_issue(starred[0], message=message)
 
 
 @ErrorFinder.register_rule(type='annassign')
@@ -1079,8 +1106,12 @@ class _CheckAssignmentRule(SyntaxRule):
                     error = "starred"
                 else:
                     self.add_issue(node, message="can't use starred expression here")
-            elif not search_ancestor(node, *_STAR_EXPR_PARENTS) and not is_aug_assign:
-                self.add_issue(node, message="starred assignment target must be in a list or tuple")
+            else:
+                ancestor = _skip_parens_bottom_up(node)
+                if ancestor.type not in _STAR_EXPR_PARENTS and not is_aug_assign \
+                        and not (ancestor.type == 'atom' and ancestor.children[0] == '['):
+                    message = "starred assignment target must be in a list or tuple"
+                    self.add_issue(node, message=message)
 
             self._check_assignment(node.children[1])
 

test/failing_examples.py

@@ -145,6 +145,44 @@ FAILING_EXAMPLES = [
     '([False], a) = x',
     'def x(): from math import *',
 
+    # invalid del statements
+    'del x + y',
+    'del x(y)',
+    'async def foo(): del await x',
+    'def foo(): del (yield x)',
+    'del [x for x in range(10)]',
+    'del *x',
+    'del *x,',
+    'del (*x,)',
+    'del [*x]',
+    'del x, *y',
+    'del *x.y,',
+    'del *x[y],',
+    'del *x[y::], z',
+    'del x, (y, *z)',
+    'del (x, *[y, z])',
+    'del [x, *(y, [*z])]',
+    'del {}',
+    'del {x}',
+    'del {x, y}',
+    'del {x, *y}',
+
+    # invalid starred expressions
+    '*x',
+    '(*x)',
+    '((*x))',
+    '1 + (*x)',
+    '*x; 1',
+    '1; *x',
+    '1\n*x',
+    'x = *y',
+    'x: int = *y',
+    'def foo(): return *x',
+    'def foo(): yield *x',
+    'f"{*x}"',
+    'for *x in 1: pass',
+    '[1 for *x in 1]',
+
     # str/bytes combinations
     '"s" b""',
     '"s" b"" ""',
@@ -198,6 +236,9 @@ FAILING_EXAMPLES = [
     '[*[] for a in [1]]',
     'async def bla():\n def x():  await bla()',
     'del None',
+    'del True',
+    'del False',
+    'del ...',
 
     # Errors of global / nonlocal
     dedent('''

test/test_python_errors.py

@@ -415,11 +415,32 @@ def test_unparenthesized_genexp(source, no_errors):
         ('*x = 2', False),
         ('(*y) = 1', False),
         ('((*z)) = 1', False),
+        ('*a,', True),
+        ('*a, = 1', True),
+        ('(*a,)', True),
+        ('(*a,) = 1', True),
+        ('[*a]', True),
+        ('[*a] = 1', True),
+        ('a, *b', True),
         ('a, *b = 1', True),
+        ('a, *b, c', True),
         ('a, *b, c = 1', True),
+        ('a, (*b), c', True),
         ('a, (*b), c = 1', True),
+        ('a, ((*b)), c', True),
         ('a, ((*b)), c = 1', True),
+        ('a, (*b, c), d', True),
         ('a, (*b, c), d = 1', True),
+        ('*a.b,', True),
+        ('*a.b, = 1', True),
+        ('*a[b],', True),
+        ('*a[b], = 1', True),
+        ('*a[b::], c', True),
+        ('*a[b::], c = 1', True),
+        ('(a, *[b, c])', True),
+        ('(a, *[b, c]) = 1', True),
+        ('[a, *(b, [*c])]', True),
+        ('[a, *(b, [*c])] = 1', True),
         ('[*(1,2,3)]', True),
         ('{*(1,2,3)}', True),
         ('[*(1,2,3),]', True),
@@ -432,3 +453,35 @@ def test_unparenthesized_genexp(source, no_errors):
 )
 def test_starred_expr(source, no_errors):
     assert bool(_get_error_list(source, version="3")) ^ no_errors
+
+
+@pytest.mark.parametrize(
+    'code', [
+        '() = ()',
+        '() = []',
+        '[] = ()',
+        '[] = []',
+    ]
+)
+def test_valid_empty_assignment(code):
+    assert not _get_error_list(code)
+
+
+@pytest.mark.parametrize(
+    'code', [
+        'del ()',
+        'del []',
+        'del x',
+        'del x,',
+        'del x, y',
+        'del (x, y)',
+        'del [x, y]',
+        'del (x, [y, z])',
+        'del x.y, x[y]',
+        'del f(x)[y::]',
+        'del x[[*y]]',
+        'del x[[*y]::]',
+    ]
+)
+def test_valid_del(code):
+    assert not _get_error_list(code)