Fix unstable formatting involving unwrapping multiple parentheses (#836) (#961)

This change also unwraps all unnecessary parentheses.

black.py

@@ -2882,7 +2882,15 @@ def normalize_invisible_parens(node: Node, parens_after: Set[str]) -> None:
             if is_walrus_assignment(child):
                 continue
             if child.type == syms.atom:
-                if maybe_make_parens_invisible_in_atom(child, parent=node):
+                # Determines if the underlying atom should be surrounded with
+                # invisible params - also makes parens invisible recursively
+                # within the atom and removes repeated invisible parens within
+                # the atom
+                should_surround_with_parens = maybe_make_parens_invisible_in_atom(
+                    child, parent=node
+                )
+
+                if should_surround_with_parens:
                     lpar = Leaf(token.LPAR, "")
                     rpar = Leaf(token.RPAR, "")
                     index = child.remove() or 0
@@ -2999,6 +3007,8 @@ def generate_ignored_nodes(leaf: Leaf) -> Iterator[LN]:
 
 def maybe_make_parens_invisible_in_atom(node: LN, parent: LN) -> bool:
     """If it's safe, make the parens in the atom `node` invisible, recursively.
+    Additionally, remove repeated, adjacent invisible parens from the atom `node`
+    as they are redundant.
 
     Returns whether the node should itself be wrapped in invisible parentheses.
 
@@ -3015,15 +3025,40 @@ def maybe_make_parens_invisible_in_atom(node: LN, parent: LN) -> bool:
     first = node.children[0]
     last = node.children[-1]
     if first.type == token.LPAR and last.type == token.RPAR:
+        middle = node.children[1]
         # make parentheses invisible
         first.value = ""  # type: ignore
         last.value = ""  # type: ignore
-        maybe_make_parens_invisible_in_atom(node.children[1], parent=parent)
+        maybe_make_parens_invisible_in_atom(middle, parent=parent)
+
+        if is_atom_with_invisible_parens(middle):
+            # Strip the invisible parens from `middle` by replacing
+            # it with the child in-between the invisible parens
+            middle.replace(middle.children[1])
+
         return False
 
     return True
 
 
+def is_atom_with_invisible_parens(node: LN) -> bool:
+    """Given a `LN`, determines whether it's an atom `node` with invisible
+    parens. Useful in dedupe-ing and normalizing parens.
+    """
+    if isinstance(node, Leaf) or node.type != syms.atom:
+        return False
+
+    first, last = node.children[0], node.children[-1]
+    return (
+        isinstance(first, Leaf)
+        and first.type == token.LPAR
+        and first.value == ""
+        and isinstance(last, Leaf)
+        and last.type == token.RPAR
+        and last.value == ""
+    )
+
+
 def is_empty_tuple(node: LN) -> bool:
     """Return True if `node` holds an empty tuple."""
     return (

tests/data/remove_parens.py

@@ -3,8 +3,118 @@
 x = (1.2)
 (x) = (3)
 
+
+def example():
+    return (("xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx"))
+
+
+def example1():
+    return ((1111111111111111111111111111111111111111111111111111111111111111111111111111111111111))
+
+
+def example1point5():
+    return ((((((1111111111111111111111111111111111111111111111111111111111111111111111111111111111111))))))
+
+
+def example2():
+    return (("xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx"))
+
+
+def example3():
+    return ((1111111111111111111111111111111111111111111111111111111111111111111111111111111))
+
+
+def example4():
+    return ((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((True))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))
+
+
+def example5():
+    return ((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((()))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))
+
+
+def example6():
+    return ((((((((({a:a for a in [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17]})))))))))
+
+
+def example7():
+    return ((((((((({a:a for a in [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20000000000000000000]})))))))))
+
+
+def example8():
+    return (((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((None)))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))
+
+
 # output
 print(1)
 x = 1
 x = 1.2
 x = 3
+
+
+def example():
+    return "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx"
+
+
+def example1():
+    return 1111111111111111111111111111111111111111111111111111111111111111111111111111111111111
+
+
+def example1point5():
+    return 1111111111111111111111111111111111111111111111111111111111111111111111111111111111111
+
+
+def example2():
+    return (
+        "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx"
+    )
+
+
+def example3():
+    return (
+        1111111111111111111111111111111111111111111111111111111111111111111111111111111
+    )
+
+
+def example4():
+    return True
+
+
+def example5():
+    return ()
+
+
+def example6():
+    return {a: a for a in [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17]}
+
+
+def example7():
+    return {
+        a: a
+        for a in [
+            1,
+            2,
+            3,
+            4,
+            5,
+            6,
+            7,
+            8,
+            9,
+            10,
+            11,
+            12,
+            13,
+            14,
+            15,
+            16,
+            17,
+            18,
+            19,
+            20000000000000000000,
+        ]
+    }
+
+
+def example8():
+    return None
+