Fix regression: unexpected parentheses around non-mathematical powers

This was caused by an overly liberal application of parentheses in #909 that
fixed #646.

Fixes #1041

black.py

@@ -1717,19 +1717,6 @@ def visit_default(self, node: LN) -> Iterator[Line]:
                 self.current_line.append(node)
         yield from super().visit_default(node)
 
-    def visit_factor(self, node: Node) -> Iterator[Line]:
-        """Force parentheses between a unary op and a binary power:
-
-        -2 ** 8 -> -(2 ** 8)
-        """
-        child = node.children[1]
-        if child.type == syms.power and len(child.children) == 3:
-            lpar = Leaf(token.LPAR, "(")
-            rpar = Leaf(token.RPAR, ")")
-            index = child.remove() or 0
-            node.insert_child(index, Node(syms.atom, [lpar, child, rpar]))
-        yield from self.visit_default(node)
-
     def visit_INDENT(self, node: Node) -> Iterator[Line]:
         """Increase indentation level, maybe yield a line."""
         # In blib2to3 INDENT never holds comments.
@@ -1829,6 +1816,23 @@ def visit_STANDALONE_COMMENT(self, leaf: Leaf) -> Iterator[Line]:
             yield from self.line()
         yield from self.visit_default(leaf)
 
+    def visit_factor(self, node: Node) -> Iterator[Line]:
+        """Force parentheses between a unary op and a binary power:
+
+        -2 ** 8 -> -(2 ** 8)
+        """
+        _operator, operand = node.children
+        if (
+            operand.type == syms.power
+            and len(operand.children) == 3
+            and operand.children[1].type == token.DOUBLESTAR
+        ):
+            lpar = Leaf(token.LPAR, "(")
+            rpar = Leaf(token.RPAR, ")")
+            index = operand.remove() or 0
+            node.insert_child(index, Node(syms.atom, [lpar, operand, rpar]))
+        yield from self.visit_default(node)
+
     def __attrs_post_init__(self) -> None:
         """You are in a twisty little maze of passages."""
         v = self.visit_stmt

tests/data/function2.py

@@ -7,9 +7,10 @@ def f(
             result = (
                 CliRunner().invoke(black.main, [str(src1), str(src2), "--diff", "--check"])
             )
+    limited.append(-limited.pop())  # negate top
     return A(
         very_long_argument_name1=very_long_value_for_the_argument,
-        very_long_argument_name2=very_long_value_for_the_argument,
+        very_long_argument_name2=-very.long.value.for_the_argument,
         **kwargs,
     )
 def g():
@@ -30,9 +31,10 @@ def f(a, **kwargs,) -> A:
             result = CliRunner().invoke(
                 black.main, [str(src1), str(src2), "--diff", "--check"]
             )
+    limited.append(-limited.pop())  # negate top
     return A(
         very_long_argument_name1=very_long_value_for_the_argument,
-        very_long_argument_name2=very_long_value_for_the_argument,
+        very_long_argument_name2=-very.long.value.for_the_argument,
         **kwargs,
     )