Draft for Black 2023 stable style

CHANGES.md

@@ -10,6 +10,35 @@
 
 <!-- Changes that affect Black's stable style -->
 
+- Introduce the 2023 stable style, which incorporates most aspects of last year's
+  preview style (#3418). Specific changes:
+  - Enforce empty lines before classes and functions with sticky leading comments
+    (#3302) (22.12.0)
+  - Reformat empty and whitespace-only files as either an empty file (if no newline is
+    present) or as a single newline character (if a newline is present) (#3348)
+    (22.12.0)
+  - Implicitly concatenated strings used as function args are now wrapped inside
+    parentheses (#3307) (22.12.0)
+  - Correctly handle trailing commas that are inside a line's leading non-nested parens
+    (#3370) (22.12.0)
+  - `--skip-string-normalization` / `-S` now prevents docstring prefixes from being
+    normalized as expected (#3168) (since 22.8.0)
+  - When using `--skip-magic-trailing-comma` or `-C`, trailing commas are stripped from
+    subscript expressions with more than 1 element (#3209) (22.8.0)
+  - Implicitly concatenated strings inside a list, set, or tuple are now wrapped inside
+    parentheses (#3162) (22.8.0)
+  - Fix a string merging/split issue when a comment is present in the middle of
+    implicitly concatenated strings on its own line (#3227) (22.8.0)
+  - Docstring quotes are no longer moved if it would violate the line length limit
+    (#3044, #3430) (22.6.0)
+  - Parentheses around return annotations are now managed (#2990) (22.6.0)
+  - Remove unnecessary parentheses around awaited objects (#2991) (22.6.0)
+  - Remove unnecessary parentheses in `with` statements (#2926) (22.6.0)
+  - Remove trailing newlines after code block open (#3035) (22.6.0)
+  - Code cell separators `#%%` are now standardised to `# %%` (#2919) (22.3.0)
+  - Remove unnecessary parentheses from `except` statements (#2939) (22.3.0)
+  - Remove unnecessary parentheses from tuple unpacking in `for` loops (#2945) (22.3.0)
+  - Avoid magic-trailing-comma in single-element subscripts (#2942) (22.3.0)
 - Fix a crash when a colon line is marked between `# fmt: off` and `# fmt: on` (#3439)
 
 ### Preview style

src/black/__init__.py

@@ -925,9 +925,6 @@ def format_file_contents(src_contents: str, *, fast: bool, mode: Mode) -> FileCo
     valid by calling :func:`assert_equivalent` and :func:`assert_stable` on it.
     `mode` is passed to :func:`format_str`.
     """
-    if not mode.preview and not src_contents.strip():
-        raise NothingChanged
-
     if mode.is_ipynb:
         dst_contents = format_ipynb_string(src_contents, fast=fast, mode=mode)
     else:
@@ -1022,7 +1019,7 @@ def format_ipynb_string(src_contents: str, *, fast: bool, mode: Mode) -> FileCon
     Operate cell-by-cell, only on code cells, only for Python notebooks.
     If the ``.ipynb`` originally had a trailing newline, it'll be preserved.
     """
-    if mode.preview and not src_contents:
+    if not src_contents:
         raise NothingChanged
 
     trailing_newline = src_contents[-1] == "\n"
@@ -1101,7 +1098,7 @@ def _format_str_once(src_contents: str, *, mode: Mode) -> str:
         for feature in {Feature.PARENTHESIZED_CONTEXT_MANAGERS}
         if supports_feature(versions, feature)
     }
-    normalize_fmt_off(src_node, preview=mode.preview)
+    normalize_fmt_off(src_node)
     lines = LineGenerator(mode=mode, features=context_manager_features)
     elt = EmptyLineTracker(mode=mode)
     split_line_features = {
@@ -1122,7 +1119,7 @@ def _format_str_once(src_contents: str, *, mode: Mode) -> str:
     dst_contents = []
     for block in dst_blocks:
         dst_contents.extend(block.all_lines())
-    if mode.preview and not dst_contents:
+    if not dst_contents:
         # Use decode_bytes to retrieve the correct source newline (CRLF or LF),
         # and check if normalized_content has more than one line
         normalized_content, _, newline = decode_bytes(src_contents.encode("utf-8"))

src/black/comments.py

@@ -29,7 +29,7 @@
 FMT_PASS: Final = {*FMT_OFF, *FMT_SKIP}
 FMT_ON: Final = {"# fmt: on", "# fmt:on", "# yapf: enable"}
 
-COMMENT_EXCEPTIONS = {True: " !:#'", False: " !:#'%"}
+COMMENT_EXCEPTIONS = " !:#'"
 
 
 @dataclass
@@ -50,7 +50,7 @@ class ProtoComment:
     consumed: int  # how many characters of the original leaf's prefix did we consume
 
 
-def generate_comments(leaf: LN, *, preview: bool) -> Iterator[Leaf]:
+def generate_comments(leaf: LN) -> Iterator[Leaf]:
     """Clean the prefix of the `leaf` and generate comments from it, if any.
 
     Comments in lib2to3 are shoved into the whitespace prefix.  This happens
@@ -69,16 +69,12 @@ def generate_comments(leaf: LN, *, preview: bool) -> Iterator[Leaf]:
     Inline comments are emitted as regular token.COMMENT leaves.  Standalone
     are emitted with a fake STANDALONE_COMMENT token identifier.
     """
-    for pc in list_comments(
-        leaf.prefix, is_endmarker=leaf.type == token.ENDMARKER, preview=preview
-    ):
+    for pc in list_comments(leaf.prefix, is_endmarker=leaf.type == token.ENDMARKER):
         yield Leaf(pc.type, pc.value, prefix="\n" * pc.newlines)
 
 
 @lru_cache(maxsize=4096)
-def list_comments(
-    prefix: str, *, is_endmarker: bool, preview: bool
-) -> List[ProtoComment]:
+def list_comments(prefix: str, *, is_endmarker: bool) -> List[ProtoComment]:
     """Return a list of :class:`ProtoComment` objects parsed from the given `prefix`."""
     result: List[ProtoComment] = []
     if not prefix or "#" not in prefix:
@@ -104,7 +100,7 @@ def list_comments(
             comment_type = token.COMMENT  # simple trailing comment
         else:
             comment_type = STANDALONE_COMMENT
-        comment = make_comment(line, preview=preview)
+        comment = make_comment(line)
         result.append(
             ProtoComment(
                 type=comment_type, value=comment, newlines=nlines, consumed=consumed
@@ -114,7 +110,7 @@ def list_comments(
     return result
 
 
-def make_comment(content: str, *, preview: bool) -> str:
+def make_comment(content: str) -> str:
     """Return a consistently formatted comment from the given `content` string.
 
     All comments (except for "##", "#!", "#:", '#'") should have a single
@@ -135,26 +131,26 @@ def make_comment(content: str, *, preview: bool) -> str:
         and not content.lstrip().startswith("type:")
     ):
         content = " " + content[1:]  # Replace NBSP by a simple space
-    if content and content[0] not in COMMENT_EXCEPTIONS[preview]:
+    if content and content[0] not in COMMENT_EXCEPTIONS:
         content = " " + content
     return "#" + content
 
 
-def normalize_fmt_off(node: Node, *, preview: bool) -> None:
+def normalize_fmt_off(node: Node) -> None:
     """Convert content between `# fmt: off`/`# fmt: on` into standalone comments."""
     try_again = True
     while try_again:
-        try_again = convert_one_fmt_off_pair(node, preview=preview)
+        try_again = convert_one_fmt_off_pair(node)
 
 
-def convert_one_fmt_off_pair(node: Node, *, preview: bool) -> bool:
+def convert_one_fmt_off_pair(node: Node) -> bool:
     """Convert content of a single `# fmt: off`/`# fmt: on` into a standalone comment.
 
     Returns True if a pair was converted.
     """
     for leaf in node.leaves():
         previous_consumed = 0
-        for comment in list_comments(leaf.prefix, is_endmarker=False, preview=preview):
+        for comment in list_comments(leaf.prefix, is_endmarker=False):
             if comment.value not in FMT_PASS:
                 previous_consumed = comment.consumed
                 continue
@@ -169,7 +165,7 @@ def convert_one_fmt_off_pair(node: Node, *, preview: bool) -> bool:
                     if comment.value in FMT_SKIP and prev.type in WHITESPACE:
                         continue
 
-            ignored_nodes = list(generate_ignored_nodes(leaf, comment, preview=preview))
+            ignored_nodes = list(generate_ignored_nodes(leaf, comment))
             if not ignored_nodes:
                 continue
 
@@ -214,26 +210,24 @@ def convert_one_fmt_off_pair(node: Node, *, preview: bool) -> bool:
     return False
 
 
-def generate_ignored_nodes(
-    leaf: Leaf, comment: ProtoComment, *, preview: bool
-) -> Iterator[LN]:
+def generate_ignored_nodes(leaf: Leaf, comment: ProtoComment) -> Iterator[LN]:
     """Starting from the container of `leaf`, generate all leaves until `# fmt: on`.
 
     If comment is skip, returns leaf only.
     Stops at the end of the block.
     """
     if comment.value in FMT_SKIP:
-        yield from _generate_ignored_nodes_from_fmt_skip(leaf, comment, preview=preview)
+        yield from _generate_ignored_nodes_from_fmt_skip(leaf, comment)
         return
     container: Optional[LN] = container_of(leaf)
     while container is not None and container.type != token.ENDMARKER:
-        if is_fmt_on(container, preview=preview):
+        if is_fmt_on(container):
             return
 
         # fix for fmt: on in children
-        if children_contains_fmt_on(container, preview=preview):
+        if children_contains_fmt_on(container):
             for index, child in enumerate(container.children):
-                if isinstance(child, Leaf) and is_fmt_on(child, preview=preview):
+                if isinstance(child, Leaf) and is_fmt_on(child):
                     if child.type in CLOSING_BRACKETS:
                         # This means `# fmt: on` is placed at a different bracket level
                         # than `# fmt: off`. This is an invalid use, but as a courtesy,
@@ -244,14 +238,12 @@ def generate_ignored_nodes(
                 if (
                     child.type == token.INDENT
                     and index < len(container.children) - 1
-                    and children_contains_fmt_on(
-                        container.children[index + 1], preview=preview
-                    )
+                    and children_contains_fmt_on(container.children[index + 1])
                 ):
                     # This means `# fmt: on` is placed right after an indentation
                     # level, and we shouldn't swallow the previous INDENT token.
                     return
-                if children_contains_fmt_on(child, preview=preview):
+                if children_contains_fmt_on(child):
                     return
                 yield child
         else:
@@ -264,14 +256,14 @@ def generate_ignored_nodes(
 
 
 def _generate_ignored_nodes_from_fmt_skip(
-    leaf: Leaf, comment: ProtoComment, *, preview: bool
+    leaf: Leaf, comment: ProtoComment
 ) -> Iterator[LN]:
     """Generate all leaves that should be ignored by the `# fmt: skip` from `leaf`."""
     prev_sibling = leaf.prev_sibling
     parent = leaf.parent
     # Need to properly format the leaf prefix to compare it to comment.value,
     # which is also formatted
-    comments = list_comments(leaf.prefix, is_endmarker=False, preview=preview)
+    comments = list_comments(leaf.prefix, is_endmarker=False)
     if not comments or comment.value != comments[0].value:
         return
     if prev_sibling is not None:
@@ -305,24 +297,24 @@ def _generate_ignored_nodes_from_fmt_skip(
         yield from iter(ignored_nodes)
 
 
-def is_fmt_on(container: LN, preview: bool) -> bool:
+def is_fmt_on(container: LN) -> bool:
     """Determine whether formatting is switched on within a container.
     Determined by whether the last `# fmt:` comment is `on` or `off`.
     """
     fmt_on = False
-    for comment in list_comments(container.prefix, is_endmarker=False, preview=preview):
+    for comment in list_comments(container.prefix, is_endmarker=False):
         if comment.value in FMT_ON:
             fmt_on = True
         elif comment.value in FMT_OFF:
             fmt_on = False
     return fmt_on
 
 
-def children_contains_fmt_on(container: LN, *, preview: bool) -> bool:
+def children_contains_fmt_on(container: LN) -> bool:
     """Determine if children have formatting switched on."""
     for child in container.children:
         leaf = first_leaf_of(child)
-        if leaf is not None and is_fmt_on(leaf, preview=preview):
+        if leaf is not None and is_fmt_on(leaf):
             return True
 
     return False