fix: Remove parenthesis around sole list items

Signed-off-by: cobalt <[email protected]>

docs/the_black_code_style/future_style.md

@@ -47,8 +47,8 @@ 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))
+- `condence_nested_brackets`: more compact formatting of nested brackets
+  ([see below](labels/hug-parens))
 
 (labels/hug-parens)=
 
@@ -124,6 +124,45 @@ foo(
 )
 ```
 
+Parenthesises around sole list items will also be removed for similar reasons. Trailing
+commas are respected here as well. For example:
+
+```python
+items = [
+    (
+        long_variable_name
+        and even_longer_variable_name
+        and yet_another_very_long_variable_name
+    )
+]
+
+items = [
+    (
+        long_variable_name
+        and even_longer_variable_name
+        and yet_another_very_long_variable_name
+    ),
+]
+```
+
+will be changed to:
+
+```python
+items = [
+    long_variable_name
+    and even_longer_variable_name
+    and yet_another_very_long_variable_name
+]
+
+items = [
+    (
+        long_variable_name
+        and even_longer_variable_name
+        and yet_another_very_long_variable_name
+    ),
+]
+```
+
 (labels/string-processing)=
 
 ### Improved string processing

src/black/linegen.py

@@ -501,6 +501,19 @@ def visit_STRING(self, leaf: Leaf) -> Iterator[Line]:
 
         yield from self.visit_default(leaf)
 
+    def visit_atom(self, node: Node) -> Iterator[Line]:
+        """Visit any atom"""
+        if (
+            Preview.condence_nested_brackets in self.mode
+            and len(node.children) == 3
+            and node.children[0].type == token.LSQB
+            and node.children[-1].type == token.RSQB
+        ):
+            # Lists of one item
+            maybe_make_parens_invisible_in_atom(node.children[1], parent=node)
+
+        yield from self.visit_default(node)
+
     def __post_init__(self) -> None:
         """You are in a twisty little maze of passages."""
         self.current_line = Line(mode=self.mode)
@@ -811,7 +824,7 @@ def _first_right_hand_split(
 
     body: Optional[Line] = None
     if (
-        Preview.hug_parens_with_braces_and_square_brackets in line.mode
+        Preview.condence_nested_brackets in line.mode
         and tail_leaves[0].value
         and tail_leaves[0].opening_bracket is head_leaves[-1]
     ):
@@ -883,19 +896,25 @@ def _maybe_split_omitting_optional_parens(
     features: Collection[Feature] = (),
     omit: Collection[LeafID] = (),
 ) -> Iterator[Line]:
-    if (
+    both_optional_parens = (
         Feature.FORCE_OPTIONAL_PARENTHESES not in features
-        # the opening bracket is an optional paren
         and rhs.opening_bracket.type == token.LPAR
         and not rhs.opening_bracket.value
-        # the closing bracket is an optional paren
         and rhs.closing_bracket.type == token.RPAR
         and not rhs.closing_bracket.value
+    )
+    if (
+        # If both brackets are optional parens
+        both_optional_parens
         # it's not an import (optional parens are the only thing we can split on
         # in this case; attempting a split without them is a waste of time)
         and not line.is_import
         # and we can actually remove the parens
-        and can_omit_invisible_parens(rhs, mode.line_length)
+        and can_omit_invisible_parens(
+            rhs,
+            mode.line_length,
+            Preview.condence_nested_brackets in mode and line.inside_brackets,
+        )
     ):
         omit = {id(rhs.closing_bracket), *omit}
         try:

src/black/lines.py

@@ -929,6 +929,7 @@ def can_be_split(line: Line) -> bool:
 def can_omit_invisible_parens(
     rhs: RHSResult,
     line_length: int,
+    inside_brackets: bool,
 ) -> bool:
     """Does `rhs.body` have a shape safe to reformat without optional parens around it?
 
@@ -962,8 +963,9 @@ def can_omit_invisible_parens(
     max_priority = bt.max_delimiter_priority()
     delimiter_count = bt.delimiter_count_with_priority(max_priority)
     if delimiter_count > 1:
-        # With more than one delimiter of a kind the optional parentheses read better.
-        return False
+        # With more than one delimiter of a kind the optional parentheses read
+        # better, but they're redundant if we're already inside brackets.
+        return inside_brackets
 
     if delimiter_count == 1:
         if max_priority == COMMA_PRIORITY and rhs.head.is_with_or_async_with_stmt:

src/black/mode.py

@@ -171,7 +171,7 @@ class Preview(Enum):
     # NOTE: string_processing requires wrap_long_dict_values_in_parens
     # for https://github.com/psf/black/issues/3117 to be fixed.
     string_processing = auto()
-    hug_parens_with_braces_and_square_brackets = auto()
+    condence_nested_brackets = auto()
     unify_docstring_detection = auto()
     no_normalize_fmt_skip_whitespace = auto()
     wrap_long_dict_values_in_parens = auto()
@@ -191,7 +191,7 @@ class Preview(Enum):
     # See issue #4159
     Preview.multiline_string_handling,
     # See issue #4036 (crash), #4098, #4099 (proposed tweaks)
-    Preview.hug_parens_with_braces_and_square_brackets,
+    Preview.condence_nested_brackets,
 }
 
 

src/black/resources/black.schema.json

@@ -80,7 +80,7 @@
         "enum": [
           "hex_codes_in_unicode_sequences",
           "string_processing",
-          "hug_parens_with_braces_and_square_brackets",
+          "condence_nested_brackets",
           "unify_docstring_detection",
           "no_normalize_fmt_skip_whitespace",
           "wrap_long_dict_values_in_parens",

tests/data/cases/preview_remove_sole_list_item_parens.py

@@ -0,0 +1,156 @@
+# flags: --unstable
+items = [
+    (
+        {"key1": "val1", "key2": "val2", "key3": "val3"}
+        if some_var == "longstring"
+        else { "key": "val" }
+    )
+]
+items = [
+    (
+        {"key1": "val1", "key2": "val2", "key3": "val3"}
+        if some_var == "longstring"
+        else { "key": "val" }
+    ),
+]
+items = [(
+    {"key1": "val1", "key2": "val2", "key3": "val3"}
+    if some_var == "longstring"
+    else { "key": "val" }
+)]
+items = [
+    {"key1": "val1", "key2": "val2", "key3": "val3"}
+    if some_var == "longstring"
+    else {"key": "val"}
+]
+items = [
+    (
+        {"key1": "val1", "key2": "val2"} if some_var == "longstring" else { "key": "val" }
+    )
+]
+items = [(
+    {"key1": "val1", "key2": "val2"} if some_var == "" else { "key": "val" }
+)]
+items = [
+    {"key1": "val1", "key2": "val2"} if some_var == "longstring" else { "key": "val" }
+]
+items = [
+    ({"key1": "val1", "key2": "val2"} if some_var == "longstring" else { "key": "val" })
+]
+items = [({"key1": "val1", "key2": "val2"} if some_var == "" else { "key": "val" })]
+items = [{"key1": "val1", "key2": "val2"} if some_var == "" else { "key": "val" }]
+
+items = [
+    (
+        "123456890123457890123468901234567890"
+        if some_var == "longstrings"
+        else "123467890123467890"
+    )
+]
+items = [
+    {"key1": "val1", "key2": "val2", "key3": "val3"}
+    and some_var == "longstring"
+    and {"key": "val"}
+]
+items = [
+    (
+        "123456890123457890123468901234567890"
+        and some_var == "longstrings"
+        and "123467890123467890"
+    )
+]
+items = [(
+    {"key1": "val1", "key2": "val2", "key3": "val3"}
+    and some_var == "longstring"
+    and {"key": "val"}
+)]
+
+
+items = [
+    (
+        long_variable_name
+        and even_longer_variable_name
+        and yet_another_very_long_variable_name
+    )
+]
+
+items = [
+    (
+        long_variable_name
+        and even_longer_variable_name
+        and yet_another_very_long_variable_name
+    ),
+]
+
+
+# output
+items = [
+    {"key1": "val1", "key2": "val2", "key3": "val3"}
+    if some_var == "longstring"
+    else {"key": "val"}
+]
+items = [
+    (
+        {"key1": "val1", "key2": "val2", "key3": "val3"}
+        if some_var == "longstring"
+        else {"key": "val"}
+    ),
+]
+items = [
+    {"key1": "val1", "key2": "val2", "key3": "val3"}
+    if some_var == "longstring"
+    else {"key": "val"}
+]
+items = [
+    {"key1": "val1", "key2": "val2", "key3": "val3"}
+    if some_var == "longstring"
+    else {"key": "val"}
+]
+items = [
+    {"key1": "val1", "key2": "val2"} if some_var == "longstring" else {"key": "val"}
+]
+items = [{"key1": "val1", "key2": "val2"} if some_var == "" else {"key": "val"}]
+items = [
+    {"key1": "val1", "key2": "val2"} if some_var == "longstring" else {"key": "val"}
+]
+items = [
+    {"key1": "val1", "key2": "val2"} if some_var == "longstring" else {"key": "val"}
+]
+items = [{"key1": "val1", "key2": "val2"} if some_var == "" else {"key": "val"}]
+items = [{"key1": "val1", "key2": "val2"} if some_var == "" else {"key": "val"}]
+
+items = [
+    "123456890123457890123468901234567890"
+    if some_var == "longstrings"
+    else "123467890123467890"
+]
+items = [
+    {"key1": "val1", "key2": "val2", "key3": "val3"}
+    and some_var == "longstring"
+    and {"key": "val"}
+]
+items = [
+    "123456890123457890123468901234567890"
+    and some_var == "longstrings"
+    and "123467890123467890"
+]
+items = [
+    {"key1": "val1", "key2": "val2", "key3": "val3"}
+    and some_var == "longstring"
+    and {"key": "val"}
+]
+
+
+items = [
+    long_variable_name
+    and even_longer_variable_name
+    and yet_another_very_long_variable_name
+]
+
+items = [
+    (
+        long_variable_name
+        and even_longer_variable_name
+        and yet_another_very_long_variable_name
+    ),
+]