Move hug_parens_with_braces_and_square_brackets into the unstable style (#4198)

Primarily because of #4036 (a crash) but also because of the feedback
in #4098 and #4099.

CHANGES.md

@@ -14,6 +14,9 @@
 
 <!-- Changes that affect Black's preview style -->
 
+- Move the `hug_parens_with_braces_and_square_brackets` feature to the unstable style
+  due to an outstanding crash and proposed formatting tweaks (#4198)
+
 ### Configuration
 
 - _Black_ now ignores `pyproject.toml` that is missing a `tool.black` section when

docs/the_black_code_style/future_style.md

@@ -24,8 +24,6 @@ Currently, the following features are included in the preview style:
   strings
 - `unify_docstring_detection`: fix inconsistencies in whether certain strings are
   detected as docstrings
-- `hug_parens_with_braces_and_square_brackets`: more compact formatting of nested
-  brackets ([see below](labels/hug-parens))
 - `no_normalize_fmt_skip_whitespace`: whitespace before `# fmt: skip` comments is no
   longer normalized
 - `typed_params_trailing_comma`: consistently add trailing commas to typed function
@@ -41,6 +39,8 @@ The unstable style additionally includes the following features:
   ([see below](labels/wrap-long-dict-values))
 - `multiline_string_handling`: more compact formatting of expressions involving
   multiline strings ([see below](labels/multiline-string-handling))
+- `hug_parens_with_braces_and_square_brackets`: more compact formatting of nested
+  brackets ([see below](labels/hug-parens))
 
 (labels/hug-parens)=
 

src/black/mode.py

@@ -186,6 +186,8 @@ class Preview(Enum):
     Preview.wrap_long_dict_values_in_parens,
     # See issue #4159
     Preview.multiline_string_handling,
+    # See issue #4036 (crash), #4098, #4099 (proposed tweaks)
+    Preview.hug_parens_with_braces_and_square_brackets,
 }
 
 

tests/data/cases/preview_hug_parens_with_braces_and_square_brackets.py

@@ -1,4 +1,4 @@
-# flags: --preview
+# flags: --unstable
 def foo_brackets(request):
     return JsonResponse(
         {

tests/data/cases/preview_hug_parens_with_braces_and_square_brackets_no_ll1.py

@@ -1,4 +1,4 @@
-# flags: --preview --no-preview-line-length-1
+# flags: --unstable --no-preview-line-length-1
 # split out from preview_hug_parens_with_brackes_and_square_brackets, as it produces
 # different code on the second pass with line-length 1 in many cases.
 # Seems to be about whether the last string in a sequence gets wrapped in parens or not.