Strip even more redundant for parentheses

CHANGES.md

@@ -28,6 +28,8 @@
   subscript expressions with more than 1 element (#3209)
 - Fix a string merging/split issue when a comment is present in the middle of implicitly
   concatenated strings on its own line (#3227)
+- All unnecessary parentheses in `for` assignments are now removed, previously certain
+  redundant parentheses were still kept (#3243)
 
 ### _Blackd_
 

src/black/linegen.py

@@ -190,7 +190,7 @@ def visit_funcdef(self, node: Node) -> Iterator[Line]:
                         if maybe_make_parens_invisible_in_atom(
                             child,
                             parent=node,
-                            remove_brackets_around_comma=False,
+                            remove_parens_around_comma=False,
                         ):
                             wrap_in_parentheses(node, child, visible=False)
                     else:
@@ -951,18 +951,14 @@ def normalize_invisible_parens(
         if check_lpar:
             if (
                 preview
-                and child.type == syms.atom
+                and isinstance(child, Node)
+                and child.type in (syms.atom, syms.exprlist)
                 and node.type == syms.for_stmt
                 and isinstance(child.prev_sibling, Leaf)
                 and child.prev_sibling.type == token.NAME
                 and child.prev_sibling.value == "for"
             ):
-                if maybe_make_parens_invisible_in_atom(
-                    child,
-                    parent=node,
-                    remove_brackets_around_comma=True,
-                ):
-                    wrap_in_parentheses(node, child, visible=False)
+                remove_for_target_parens(child, node)
             elif preview and isinstance(child, Node) and node.type == syms.with_stmt:
                 remove_with_parens(child, node)
             elif child.type == syms.atom:
@@ -1015,7 +1011,7 @@ def remove_await_parens(node: Node) -> None:
             if maybe_make_parens_invisible_in_atom(
                 node.children[1],
                 parent=node,
-                remove_brackets_around_comma=True,
+                remove_parens_around_comma=True,
             ):
                 wrap_in_parentheses(node, node.children[1], visible=False)
 
@@ -1042,6 +1038,28 @@ def remove_await_parens(node: Node) -> None:
                 remove_await_parens(bracket_contents)
 
 
+def remove_for_target_parens(node: Node, parent: Node) -> None:
+    """Recursively hide optional parens in `for` statements."""
+    # The main goal is to run `maybe_make_parens_invisible_in_atom` on every atom Node
+    # between "for" and "in".
+    if node.type == syms.atom:
+        # Parenthesized group of nodes/leaves, eg. `(x, y)`
+        # First try removing the group's surrounding parentheses.
+        if maybe_make_parens_invisible_in_atom(
+            node, parent, remove_parens_around_comma=(parent.type == syms.for_stmt)
+        ):
+            wrap_in_parentheses(parent, node, visible=False)
+        # Then check if this atom could contain more atoms.
+        middle = node.children[1]
+        if isinstance(middle, Node):
+            remove_for_target_parens(middle, node)
+    elif node.type in (syms.exprlist, syms.testlist_gexp):
+        # A series of nodes/leaves separated by commas, eg. `(x), (y)`
+        for c in node.children:
+            if isinstance(c, Node) and c.type == syms.atom:
+                remove_for_target_parens(c, node)
+
+
 def remove_with_parens(node: Node, parent: Node) -> None:
     """Recursively hide optional parens in `with` statements."""
     # Removing all unnecessary parentheses in with statements in one pass is a tad
@@ -1064,7 +1082,7 @@ def remove_with_parens(node: Node, parent: Node) -> None:
         if maybe_make_parens_invisible_in_atom(
             node,
             parent=parent,
-            remove_brackets_around_comma=True,
+            remove_parens_around_comma=True,
         ):
             wrap_in_parentheses(parent, node, visible=False)
         if isinstance(node.children[1], Node):
@@ -1079,15 +1097,16 @@ def remove_with_parens(node: Node, parent: Node) -> None:
         if maybe_make_parens_invisible_in_atom(
             node.children[0],
             parent=node,
-            remove_brackets_around_comma=True,
+            remove_parens_around_comma=True,
         ):
             wrap_in_parentheses(node, node.children[0], visible=False)
 
 
 def maybe_make_parens_invisible_in_atom(
     node: LN,
     parent: LN,
-    remove_brackets_around_comma: bool = False,
+    *,
+    remove_parens_around_comma: bool = False,
 ) -> bool:
     """If it's safe, make the parens in the atom `node` invisible, recursively.
     Additionally, remove repeated, adjacent invisible parens from the atom `node`
@@ -1101,10 +1120,10 @@ def maybe_make_parens_invisible_in_atom(
         or is_one_tuple(node)
         or (is_yield(node) and parent.type != syms.expr_stmt)
         or (
-            # This condition tries to prevent removing non-optional brackets
+            # This condition tries to prevent removing non-optional parentheses
             # around a tuple, however, can be a bit overzealous so we provide
             # and option to skip this check for `for` and `with` statements.
-            not remove_brackets_around_comma
+            not remove_parens_around_comma
             and max_delimiter_priority_in_atom(node) >= COMMA_PRIORITY
         )
     ):
@@ -1132,7 +1151,7 @@ def maybe_make_parens_invisible_in_atom(
         maybe_make_parens_invisible_in_atom(
             middle,
             parent=parent,
-            remove_brackets_around_comma=remove_brackets_around_comma,
+            remove_parens_around_comma=remove_parens_around_comma,
         )
 
         if is_atom_with_invisible_parens(middle):

tests/data/preview/remove_for_brackets.py

@@ -1,3 +1,6 @@
+for (((x))) in points:
+    pass
+
 # Only remove tuple brackets after `for`
 for (k, v) in d.items():
     print(k, v)
@@ -8,6 +11,15 @@
         module._verify_python3_env = lambda: None
 
 # Brackets remain for long for loop lines
+for (one_super_long_name_as_the_for_target_list_because_why_not_you_dont_control_me) in points:
+    pass
+
+for (one_super_long_name_as_the_for_target_list_because_why_not_you_dont_control_me_i_have_total_freedom) in points:
+    pass
+
+for ((many_long_name_tuples, many_long_name_tuples), (many_long_name_tuples, many_long_name_tuples), (many_long_name_tuples, many_long_name_tuples)) in points:
+    pass
+
 for (why_would_anyone_choose_to_name_a_loop_variable_with_a_name_this_long, i_dont_know_but_we_should_still_check_the_behaviour_if_they_do) in d.items():
     print(k, v)
 
@@ -18,7 +30,47 @@
 for (((((k, v))))) in d.items():
     print(k, v)
 
+# One-tuple
+for (x,) in points:
+    pass
+
+# A series of atoms that each need their brackets removed
+for (x), (y) in points:
+    pass
+
+# A mix of "simple" atoms and atoms that contain more atoms
+for ((x), (y)) in points:
+    pass
+
+for ((((x)), (((y))))) in points:
+    pass
+
+# Mixed again; some of these brackets matter.
+for ((x), (y)), z in points:
+    pass
+
+for ((x, y), z) in points:
+    pass
+
+for ((x, (((y)))), (((z)))) in points:
+    pass
+
+for (((x,), (y)), ((z)),) in points:
+    pass
+
+for ((a, b)), ((c, d)) in points:
+    pass
+
+for ((((a), (b))), (((c), (d)))) in points:
+    pass
+
+for (a, (b, (c, (d)))) in points:
+    pass
+
 # output
+for x in points:
+    pass
+
 # Only remove tuple brackets after `for`
 for k, v in d.items():
     print(k, v)
@@ -29,6 +81,21 @@
         module._verify_python3_env = lambda: None
 
 # Brackets remain for long for loop lines
+for (
+    one_super_long_name_as_the_for_target_list_because_why_not_you_dont_control_me
+) in points:
+    pass
+
+for one_super_long_name_as_the_for_target_list_because_why_not_you_dont_control_me_i_have_total_freedom in (points):
+    pass
+
+for (
+    (many_long_name_tuples, many_long_name_tuples),
+    (many_long_name_tuples, many_long_name_tuples),
+    (many_long_name_tuples, many_long_name_tuples),
+) in points:
+    pass
+
 for (
     why_would_anyone_choose_to_name_a_loop_variable_with_a_name_this_long,
     i_dont_know_but_we_should_still_check_the_behaviour_if_they_do,
@@ -46,3 +113,43 @@
 # Test deeply nested brackets
 for k, v in d.items():
     print(k, v)
+
+# One-tuple
+for (x,) in points:
+    pass
+
+# A series of atoms that each need their brackets removed
+for x, y in points:
+    pass
+
+# A mix of "simple" atoms and atoms that contain more atoms
+for x, y in points:
+    pass
+
+for x, y in points:
+    pass
+
+# Mixed again; some of these brackets matter.
+for (x, y), z in points:
+    pass
+
+for (x, y), z in points:
+    pass
+
+for (x, y), z in points:
+    pass
+
+for (
+    ((x,), y),
+    z,
+) in points:
+    pass
+
+for (a, b), (c, d) in points:
+    pass
+
+for (a, b), (c, d) in points:
+    pass
+
+for a, (b, (c, d)) in points:
+    pass