Handle more huggable immediately nested parens/brackets. (#4012)

Fixes #4011

CHANGES.md

@@ -14,6 +14,9 @@
 
 <!-- Changes that affect Black's preview style -->
 
+- Additional cases of immediately nested tuples, lists, and dictionaries are now
+  indented less (#4012)
+
 ### Configuration
 
 <!-- Changes to how Black can be configured -->

docs/conf.py

@@ -149,15 +149,13 @@ def make_pypi_svg(version: str) -> None:
 # Grouping the document tree into LaTeX files. List of tuples
 # (source start file, target name, title,
 #  author, documentclass [howto, manual, or own class]).
-latex_documents = [
-    (
-        master_doc,
-        "black.tex",
-        "Documentation for Black",
-        "Łukasz Langa and contributors to Black",
-        "manual",
-    )
-]
+latex_documents = [(
+    master_doc,
+    "black.tex",
+    "Documentation for Black",
+    "Łukasz Langa and contributors to Black",
+    "manual",
+)]
 
 
 # -- Options for manual page output ------------------------------------------
@@ -172,17 +170,15 @@ def make_pypi_svg(version: str) -> None:
 # Grouping the document tree into Texinfo files. List of tuples
 # (source start file, target name, title, author,
 #  dir menu entry, description, category)
-texinfo_documents = [
-    (
-        master_doc,
-        "Black",
-        "Documentation for Black",
-        author,
-        "Black",
-        "The uncompromising Python code formatter",
-        "Miscellaneous",
-    )
-]
+texinfo_documents = [(
+    master_doc,
+    "Black",
+    "Documentation for Black",
+    author,
+    "Black",
+    "The uncompromising Python code formatter",
+    "Miscellaneous",
+)]
 
 
 # -- Options for Epub output -------------------------------------------------

docs/the_black_code_style/future_style.md

@@ -116,8 +116,7 @@ my_dict = {
 ### Improved multiline dictionary and list indentation for sole function parameter
 
 For better readability and less verticality, _Black_ now pairs parentheses ("(", ")")
-with braces ("{", "}") and square brackets ("[", "]") on the same line for single
-parameter function calls. For example:
+with braces ("{", "}") and square brackets ("[", "]") on the same line. For example:
 
 ```python
 foo(
@@ -127,6 +126,14 @@ foo(
         3,
     ]
 )
+
+nested_array = [
+    [
+        1,
+        2,
+        3,
+    ]
+]
 ```
 
 will be changed to:
@@ -137,6 +144,12 @@ foo([
     2,
     3,
 ])
+
+nested_array = [[
+    1,
+    2,
+    3,
+]]
 ```
 
 This also applies to list and dictionary unpacking:

src/black/cache.py

@@ -124,9 +124,9 @@ def filtered_cached(self, sources: Iterable[Path]) -> Tuple[Set[Path], Set[Path]
 
     def write(self, sources: Iterable[Path]) -> None:
         """Update the cache file data and write a new cache file."""
-        self.file_data.update(**{
-            str(src.resolve()): Cache.get_file_data(src) for src in sources
-        })
+        self.file_data.update(
+            **{str(src.resolve()): Cache.get_file_data(src) for src in sources}
+        )
         try:
             CACHE_DIR.mkdir(parents=True, exist_ok=True)
             with tempfile.NamedTemporaryFile(

src/black/handle_ipynb_magics.py

@@ -17,36 +17,30 @@
 from black.output import out
 from black.report import NothingChanged
 
-TRANSFORMED_MAGICS = frozenset(
-    (
-        "get_ipython().run_cell_magic",
-        "get_ipython().system",
-        "get_ipython().getoutput",
-        "get_ipython().run_line_magic",
-    )
-)
-TOKENS_TO_IGNORE = frozenset(
-    (
-        "ENDMARKER",
-        "NL",
-        "NEWLINE",
-        "COMMENT",
-        "DEDENT",
-        "UNIMPORTANT_WS",
-        "ESCAPED_NL",
-    )
-)
-PYTHON_CELL_MAGICS = frozenset(
-    (
-        "capture",
-        "prun",
-        "pypy",
-        "python",
-        "python3",
-        "time",
-        "timeit",
-    )
-)
+TRANSFORMED_MAGICS = frozenset((
+    "get_ipython().run_cell_magic",
+    "get_ipython().system",
+    "get_ipython().getoutput",
+    "get_ipython().run_line_magic",
+))
+TOKENS_TO_IGNORE = frozenset((
+    "ENDMARKER",
+    "NL",
+    "NEWLINE",
+    "COMMENT",
+    "DEDENT",
+    "UNIMPORTANT_WS",
+    "ESCAPED_NL",
+))
+PYTHON_CELL_MAGICS = frozenset((
+    "capture",
+    "prun",
+    "pypy",
+    "python",
+    "python3",
+    "time",
+    "timeit",
+))
 TOKEN_HEX = secrets.token_hex
 
 

src/black/linegen.py

@@ -817,25 +817,66 @@ def _first_right_hand_split(
     body_leaves.reverse()
     head_leaves.reverse()
 
-    if Preview.hug_parens_with_braces_and_square_brackets in line.mode:
-        is_unpacking = 1 if body_leaves[0].type in [token.STAR, token.DOUBLESTAR] else 0
-        if (
-            tail_leaves[0].type == token.RPAR
-            and tail_leaves[0].value
-            and tail_leaves[0].opening_bracket is head_leaves[-1]
-            and body_leaves[-1].type in [token.RBRACE, token.RSQB]
-            and body_leaves[-1].opening_bracket is body_leaves[is_unpacking]
+    body: Optional[Line] = None
+    if (
+        Preview.hug_parens_with_braces_and_square_brackets in line.mode
+        and tail_leaves[0].value
+        and tail_leaves[0].opening_bracket is head_leaves[-1]
+    ):
+        inner_body_leaves = list(body_leaves)
+        hugged_opening_leaves: List[Leaf] = []
+        hugged_closing_leaves: List[Leaf] = []
+        is_unpacking = body_leaves[0].type in [token.STAR, token.DOUBLESTAR]
+        unpacking_offset: int = 1 if is_unpacking else 0
+        while (
+            len(inner_body_leaves) >= 2 + unpacking_offset
+            and inner_body_leaves[-1].type in CLOSING_BRACKETS
+            and inner_body_leaves[-1].opening_bracket
+            is inner_body_leaves[unpacking_offset]
         ):
-            head_leaves = head_leaves + body_leaves[: 1 + is_unpacking]
-            tail_leaves = body_leaves[-1:] + tail_leaves
-            body_leaves = body_leaves[1 + is_unpacking : -1]
+            if unpacking_offset:
+                hugged_opening_leaves.append(inner_body_leaves.pop(0))
+                unpacking_offset = 0
+            hugged_opening_leaves.append(inner_body_leaves.pop(0))
+            hugged_closing_leaves.insert(0, inner_body_leaves.pop())
+
+        if hugged_opening_leaves and inner_body_leaves:
+            inner_body = bracket_split_build_line(
+                inner_body_leaves,
+                line,
+                hugged_opening_leaves[-1],
+                component=_BracketSplitComponent.body,
+            )
+            if (
+                line.mode.magic_trailing_comma
+                and inner_body_leaves[-1].type == token.COMMA
+            ):
+                should_hug = True
+            else:
+                line_length = line.mode.line_length - sum(
+                    len(str(leaf))
+                    for leaf in hugged_opening_leaves + hugged_closing_leaves
+                )
+                if is_line_short_enough(
+                    inner_body, mode=replace(line.mode, line_length=line_length)
+                ):
+                    # Do not hug if it fits on a single line.
+                    should_hug = False
+                else:
+                    should_hug = True
+            if should_hug:
+                body_leaves = inner_body_leaves
+                head_leaves.extend(hugged_opening_leaves)
+                tail_leaves = hugged_closing_leaves + tail_leaves
+                body = inner_body  # No need to re-calculate the body again later.
 
     head = bracket_split_build_line(
         head_leaves, line, opening_bracket, component=_BracketSplitComponent.head
     )
-    body = bracket_split_build_line(
-        body_leaves, line, opening_bracket, component=_BracketSplitComponent.body
-    )
+    if body is None:
+        body = bracket_split_build_line(
+            body_leaves, line, opening_bracket, component=_BracketSplitComponent.body
+        )
     tail = bracket_split_build_line(
         tail_leaves, line, opening_bracket, component=_BracketSplitComponent.tail
     )