Gating change to preview style, fixed merge conflict

Author: rxjacob

CHANGES.md

@@ -18,13 +18,14 @@
 - Fix crash when multiple `# fmt: skip` comments are used in a multi-part if-clause, on
   string literals, or on dictionary entries with long lines (#4872)
 - Fix possible crash when `fmt: ` directives aren't on the top level (#4856)
-- Fix bug where `if` guards in `case` blocks were incorrectly split when the pattern had 
-  a trailing comma (#4884)
 
 ### Preview style
 
 <!-- Changes that affect Black's preview style -->
 
+- Fix bug where `if` guards in `case` blocks were incorrectly split when the pattern had 
+  a trailing comma (#4884)
+
 ### Configuration
 
 <!-- Changes to how Black can be configured -->

src/black/linegen.py

@@ -1594,7 +1594,18 @@ def normalize_invisible_parens(
                 break
 
             elif not is_multiline_string(child):
-                wrap_in_parentheses(node, child, visible=False)
+                if mode.preview:
+                    if node.type == syms.guard:
+                        mock_line = Line(mode=mode)
+                        for leaf in child.leaves():
+                            mock_line.append(leaf)
+                        # If it's a guard AND it's short, we DON'T wrap
+                        if not is_line_short_enough(mock_line, mode=mode):
+                            wrap_in_parentheses(node, child, visible=False)
+                    else:
+                        wrap_in_parentheses(node, child, visible=False)
+                else:
+                    wrap_in_parentheses(node, child, visible=False)
 
         comma_check = child.type == token.COMMA
 

tests/data/cases/preview_fmtpass_imports.py

@@ -3,8 +3,10 @@
 # Regression test for https://github.com/psf/black/issues/3438
 
 import ast
+
 import collections  # fmt: skip
 import dataclasses
+
 # fmt: off
 import os
 # fmt: on