Consistent empty lines in Change Log

[etc/vim.git] / black.py

diff --git a/black.py b/black.py
index 2c61880dda24a23dc897523f9bd37c9dd29d7ac8..537ba599807ffea932a223884a40488d22c8ab45 100644 (file)
--- a/black.py
+++ b/black.py
@@ -10,12 +10,14 @@ import logging
 from multiprocessing import Manager
 import os
 from pathlib import Path
 from multiprocessing import Manager
 import os
 from pathlib import Path

+import re

 import tokenize
 import signal
 import sys
 from typing import (
     Any,
     Callable,
 import tokenize
 import signal
 import sys
 from typing import (
     Any,
     Callable,

+    Collection,

     Dict,
     Generic,
     Iterable,
     Dict,
     Generic,
     Iterable,


@@ -38,7 +40,7 @@ from blib2to3 import pygram, pytree
 from blib2to3.pgen2 import driver, token
 from blib2to3.pgen2.parse import ParseError
 
 from blib2to3.pgen2 import driver, token
 from blib2to3.pgen2.parse import ParseError
 

-__version__ = "18.3a4"
+__version__ = "18.4a1"

 DEFAULT_LINE_LENGTH = 88
 # types
 syms = pygram.python_symbols
 DEFAULT_LINE_LENGTH = 88
 # types
 syms = pygram.python_symbols


@@ -129,6 +131,15 @@ class WriteBack(Enum):
     is_flag=True,
     help="If --fast given, skip temporary sanity checks. [default: --safe]",
 )
     is_flag=True,
     help="If --fast given, skip temporary sanity checks. [default: --safe]",
 )

+@click.option(
+    "-q",
+    "--quiet",
+    is_flag=True,
+    help=(
+        "Don't emit non-error messages to stderr. Errors are still emitted, "
+        "silence those with 2>/dev/null."
+    ),
+)

 @click.version_option(version=__version__)
 @click.argument(
     "src",
 @click.version_option(version=__version__)
 @click.argument(
     "src",


@@ -144,6 +155,7 @@ def main(
     check: bool,
     diff: bool,
     fast: bool,
     check: bool,
     diff: bool,
     fast: bool,

+    quiet: bool,

     src: List[str],
 ) -> None:
     """The uncompromising code formatter."""
     src: List[str],
 ) -> None:
     """The uncompromising code formatter."""


@@ -174,7 +186,7 @@ def main(
         ctx.exit(0)
     elif len(sources) == 1:
         p = sources[0]
         ctx.exit(0)
     elif len(sources) == 1:
         p = sources[0]

-        report = Report(check=check)
+        report = Report(check=check, quiet=quiet)

         try:
             if not p.is_file() and str(p) == "-":
                 changed = format_stdin_to_stdout(
         try:
             if not p.is_file() and str(p) == "-":
                 changed = format_stdin_to_stdout(


@@ -195,7 +207,7 @@ def main(
         try:
             return_code = loop.run_until_complete(
                 schedule_formatting(
         try:
             return_code = loop.run_until_complete(
                 schedule_formatting(

-                    sources, line_length, write_back, fast, loop, executor
+                    sources, line_length, write_back, fast, quiet, loop, executor

                 )
             )
         finally:
                 )
             )
         finally:


@@ -208,6 +220,7 @@ async def schedule_formatting(
     line_length: int,
     write_back: WriteBack,
     fast: bool,
     line_length: int,
     write_back: WriteBack,
     fast: bool,

+    quiet: bool,

     loop: BaseEventLoop,
     executor: Executor,
 ) -> int:
     loop: BaseEventLoop,
     executor: Executor,
 ) -> int:


@@ -235,7 +248,7 @@ async def schedule_formatting(
     loop.add_signal_handler(signal.SIGTERM, cancel, _task_values)
     await asyncio.wait(tasks.values())
     cancelled = []
     loop.add_signal_handler(signal.SIGTERM, cancel, _task_values)
     await asyncio.wait(tasks.values())
     cancelled = []

-    report = Report(check=not write_back)
+    report = Report(check=write_back is WriteBack.NO, quiet=quiet)

     for src, task in tasks.items():
         if not task.done():
             report.failed(src, "timed out, cancelling")
     for src, task in tasks.items():
         if not task.done():
             report.failed(src, "timed out, cancelling")


@@ -249,9 +262,10 @@ async def schedule_formatting(
             report.done(src, task.result())
     if cancelled:
         await asyncio.gather(*cancelled, loop=loop, return_exceptions=True)
             report.done(src, task.result())
     if cancelled:
         await asyncio.gather(*cancelled, loop=loop, return_exceptions=True)

-    else:
+    elif not quiet:

         out("All done! ✨ 🍰 ✨")
         out("All done! ✨ 🍰 ✨")

-    click.echo(str(report))
+    if not quiet:
+        click.echo(str(report))

     return report.return_code
 
 
     return report.return_code
 
 


@@ -302,12 +316,12 @@ def format_stdin_to_stdout(
     `line_length` and `fast` arguments are passed to :func:`format_file_contents`.
     """
     src = sys.stdin.read()
     `line_length` and `fast` arguments are passed to :func:`format_file_contents`.
     """
     src = sys.stdin.read()

+    dst = src

     try:
         dst = format_file_contents(src, line_length=line_length, fast=fast)
         return True
 
     except NothingChanged:
     try:
         dst = format_file_contents(src, line_length=line_length, fast=fast)
         return True
 
     except NothingChanged:

-        dst = src

         return False
 
     finally:
         return False
 
     finally:


@@ -549,12 +563,13 @@ class BracketTracker:
             leaf.opening_bracket = opening_bracket
         leaf.bracket_depth = self.depth
         if self.depth == 0:
             leaf.opening_bracket = opening_bracket
         leaf.bracket_depth = self.depth
         if self.depth == 0:

-            after_delim = is_split_after_delimiter(leaf, self.previous)
-            before_delim = is_split_before_delimiter(leaf, self.previous)
-            if after_delim > before_delim:
-                self.delimiters[id(leaf)] = after_delim
-            elif before_delim > after_delim and self.previous is not None:
-                self.delimiters[id(self.previous)] = before_delim
+            delim = is_split_before_delimiter(leaf, self.previous)
+            if delim and self.previous is not None:
+                self.delimiters[id(self.previous)] = delim
+            else:
+                delim = is_split_after_delimiter(leaf, self.previous)
+                if delim:
+                    self.delimiters[id(leaf)] = delim

         if leaf.type in OPENING_BRACKETS:
             self.bracket_match[self.depth, BRACKET[leaf.type]] = leaf
             self.depth += 1
         if leaf.type in OPENING_BRACKETS:
             self.bracket_match[self.depth, BRACKET[leaf.type]] = leaf
             self.depth += 1


@@ -568,6 +583,7 @@ class BracketTracker:
         """Return the highest priority of a delimiter found on the line.
 
         Values are consistent with what `is_delimiter()` returns.
         """Return the highest priority of a delimiter found on the line.
 
         Values are consistent with what `is_delimiter()` returns.

+        Raises ValueError on no delimiters.

         """
         return max(v for k, v in self.delimiters.items() if k not in exclude)
 
         """
         return max(v for k, v in self.delimiters.items() if k not in exclude)
 


@@ -594,7 +610,7 @@ class Line:
 
         Inline comments are put aside.
         """
 
         Inline comments are put aside.
         """

-        has_value = leaf.value.strip()
+        has_value = leaf.type in BRACKETS or bool(leaf.value.strip())

         if not has_value:
             return
 
         if not has_value:
             return
 


@@ -695,12 +711,12 @@ class Line:
             and self.leaves[0].value == "yield"
         )
 
             and self.leaves[0].value == "yield"
         )
 

-    @property
-    def contains_standalone_comments(self) -> bool:
+    def contains_standalone_comments(self, depth_limit: int = sys.maxsize) -> bool:

         """If so, needs to be split before emitting."""
         for leaf in self.leaves:
             if leaf.type == STANDALONE_COMMENT:
         """If so, needs to be split before emitting."""
         for leaf in self.leaves:
             if leaf.type == STANDALONE_COMMENT:

-                return True
+                if leaf.bracket_depth <= depth_limit:
+                    return True

 
         return False
 
 
         return False
 


@@ -1063,15 +1079,22 @@ class LineGenerator(Visitor[Line]):
         # DEDENT has no value. Additionally, in blib2to3 it never holds comments.
         yield from self.line(-1)
 
         # DEDENT has no value. Additionally, in blib2to3 it never holds comments.
         yield from self.line(-1)
 

-    def visit_stmt(self, node: Node, keywords: Set[str]) -> Iterator[Line]:
+    def visit_stmt(
+        self, node: Node, keywords: Set[str], parens: Set[str]
+    ) -> Iterator[Line]:

         """Visit a statement.
 
         This implementation is shared for `if`, `while`, `for`, `try`, `except`,
         """Visit a statement.
 
         This implementation is shared for `if`, `while`, `for`, `try`, `except`,

-        `def`, `with`, and `class`.
+        `def`, `with`, `class`, and `assert`.
+
+        The relevant Python language `keywords` for a given statement will be
+        NAME leaves within it. This methods puts those on a separate line.

 
 

-        The relevant Python language `keywords` for a given statement will be NAME
-        leaves within it. This methods puts those on a separate line.
+        `parens` holds pairs of nodes where invisible parentheses should be put.
+        Keys hold nodes after which opening parentheses should be put, values
+        hold nodes before which closing parentheses should be put.

         """
         """

+        normalize_invisible_parens(node, parens_after=parens)

         for child in node.children:
             if child.type == token.NAME and child.value in keywords:  # type: ignore
                 yield from self.line()
         for child in node.children:
             if child.type == token.NAME and child.value in keywords:  # type: ignore
                 yield from self.line()


@@ -1111,6 +1134,32 @@ class LineGenerator(Visitor[Line]):
             yield from self.line()
             yield from self.visit(child)
 
             yield from self.line()
             yield from self.visit(child)
 

+    def visit_import_from(self, node: Node) -> Iterator[Line]:
+        """Visit import_from and maybe put invisible parentheses.
+
+        This is separate from `visit_stmt` because import statements don't
+        support arbitrary atoms and thus handling of parentheses is custom.
+        """
+        check_lpar = False
+        for index, child in enumerate(node.children):
+            if check_lpar:
+                if child.type == token.LPAR:
+                    # make parentheses invisible
+                    child.value = ""  # type: ignore
+                    node.children[-1].value = ""  # type: ignore
+                else:
+                    # insert invisible parentheses
+                    node.insert_child(index, Leaf(token.LPAR, ""))
+                    node.append_child(Leaf(token.RPAR, ""))
+                break
+
+            check_lpar = (
+                child.type == token.NAME and child.value == "import"  # type: ignore
+            )
+
+        for child in node.children:
+            yield from self.visit(child)
+

     def visit_SEMI(self, leaf: Leaf) -> Iterator[Line]:
         """Remove a semicolon and put the other statement on a separate line."""
         yield from self.line()
     def visit_SEMI(self, leaf: Leaf) -> Iterator[Line]:
         """Remove a semicolon and put the other statement on a separate line."""
         yield from self.line()


@@ -1141,18 +1190,23 @@ class LineGenerator(Visitor[Line]):
     def __attrs_post_init__(self) -> None:
         """You are in a twisty little maze of passages."""
         v = self.visit_stmt
     def __attrs_post_init__(self) -> None:
         """You are in a twisty little maze of passages."""
         v = self.visit_stmt

-        self.visit_if_stmt = partial(v, keywords={"if", "else", "elif"})
-        self.visit_while_stmt = partial(v, keywords={"while", "else"})
-        self.visit_for_stmt = partial(v, keywords={"for", "else"})
-        self.visit_try_stmt = partial(v, keywords={"try", "except", "else", "finally"})
-        self.visit_except_clause = partial(v, keywords={"except"})
-        self.visit_funcdef = partial(v, keywords={"def"})
-        self.visit_with_stmt = partial(v, keywords={"with"})
-        self.visit_classdef = partial(v, keywords={"class"})
+        Ø: Set[str] = set()
+        self.visit_assert_stmt = partial(v, keywords={"assert"}, parens={"assert", ","})
+        self.visit_if_stmt = partial(v, keywords={"if", "else", "elif"}, parens={"if"})
+        self.visit_while_stmt = partial(v, keywords={"while", "else"}, parens={"while"})
+        self.visit_for_stmt = partial(v, keywords={"for", "else"}, parens={"for", "in"})
+        self.visit_try_stmt = partial(
+            v, keywords={"try", "except", "else", "finally"}, parens=Ø
+        )
+        self.visit_except_clause = partial(v, keywords={"except"}, parens=Ø)
+        self.visit_with_stmt = partial(v, keywords={"with"}, parens=Ø)
+        self.visit_funcdef = partial(v, keywords={"def"}, parens=Ø)
+        self.visit_classdef = partial(v, keywords={"class"}, parens=Ø)

         self.visit_async_funcdef = self.visit_async_stmt
         self.visit_decorated = self.visit_decorators
 
 
         self.visit_async_funcdef = self.visit_async_stmt
         self.visit_decorated = self.visit_decorators
 
 

+IMPLICIT_TUPLE = {syms.testlist, syms.testlist_star_expr, syms.exprlist}

 BRACKET = {token.LPAR: token.RPAR, token.LSQB: token.RSQB, token.LBRACE: token.RBRACE}
 OPENING_BRACKETS = set(BRACKET.keys())
 CLOSING_BRACKETS = set(BRACKET.values())
 BRACKET = {token.LPAR: token.RPAR, token.LSQB: token.RSQB, token.LBRACE: token.RBRACE}
 OPENING_BRACKETS = set(BRACKET.keys())
 CLOSING_BRACKETS = set(BRACKET.values())


@@ -1201,14 +1255,17 @@ def whitespace(leaf: Leaf) -> str:  # noqa C901
                     return prevp.prefix
 
         elif prevp.type == token.DOUBLESTAR:
                     return prevp.prefix
 
         elif prevp.type == token.DOUBLESTAR:

-            if prevp.parent and prevp.parent.type in {
-                syms.arglist,
-                syms.argument,
-                syms.dictsetmaker,
-                syms.parameters,
-                syms.typedargslist,
-                syms.varargslist,
-            }:
+            if (
+                prevp.parent
+                and prevp.parent.type in {
+                    syms.arglist,
+                    syms.argument,
+                    syms.dictsetmaker,
+                    syms.parameters,
+                    syms.typedargslist,
+                    syms.varargslist,
+                }
+            ):

                 return NO
 
         elif prevp.type == token.COLON:
                 return NO
 
         elif prevp.type == token.COLON:


@@ -1368,9 +1425,10 @@ def whitespace(leaf: Leaf) -> str:  # noqa C901
 
             prevp_parent = prevp.parent
             assert prevp_parent is not None
 
             prevp_parent = prevp.parent
             assert prevp_parent is not None

-            if prevp.type == token.COLON and prevp_parent.type in {
-                syms.subscript, syms.sliceop
-            }:
+            if (
+                prevp.type == token.COLON
+                and prevp_parent.type in {syms.subscript, syms.sliceop}
+            ):

                 return NO
 
             elif prevp.type == token.EQUAL and prevp_parent.type == syms.argument:
                 return NO
 
             elif prevp.type == token.EQUAL and prevp_parent.type == syms.argument:


@@ -1426,13 +1484,6 @@ def is_split_after_delimiter(leaf: Leaf, previous: Leaf = None) -> int:
     if leaf.type == token.COMMA:
         return COMMA_PRIORITY
 
     if leaf.type == token.COMMA:
         return COMMA_PRIORITY
 

-    if (
-        leaf.type in VARARGS
-        and leaf.parent
-        and leaf.parent.type in {syms.argument, syms.typedargslist}
-    ):
-        return MATH_PRIORITY
-

     return 0
 
 
     return 0
 
 


@@ -1444,6 +1495,15 @@ def is_split_before_delimiter(leaf: Leaf, previous: Leaf = None) -> int:
 
     Higher numbers are higher priority.
     """
 
     Higher numbers are higher priority.
     """

+    if (
+        leaf.type in VARARGS
+        and leaf.parent
+        and leaf.parent.type in {syms.argument, syms.typedargslist, syms.dictsetmaker}
+    ):
+        # * and ** might also be MATH_OPERATORS but in this case they are not.
+        # Don't treat them as a delimiter.
+        return 0
+

     if (
         leaf.type in MATH_OPERATORS
         and leaf.parent
     if (
         leaf.type in MATH_OPERATORS
         and leaf.parent


@@ -1591,7 +1651,7 @@ def split_line(
     if (
         len(line_str) <= line_length
         and "\n" not in line_str  # multiline strings
     if (
         len(line_str) <= line_length
         and "\n" not in line_str  # multiline strings

-        and not line.contains_standalone_comments
+        and not line.contains_standalone_comments()

     ):
         yield line
         return
     ):
         yield line
         return


@@ -1657,9 +1717,7 @@ def left_hand_split(line: Line, py36: bool = False) -> Iterator[Line]:
     if body_leaves:
         normalize_prefix(body_leaves[0], inside_brackets=True)
     # Build the new lines.
     if body_leaves:
         normalize_prefix(body_leaves[0], inside_brackets=True)
     # Build the new lines.

-    for result, leaves in (
-        (head, head_leaves), (body, body_leaves), (tail, tail_leaves)
-    ):
+    for result, leaves in (head, head_leaves), (body, body_leaves), (tail, tail_leaves):

         for leaf in leaves:
             result.append(leaf, preformatted=True)
             for comment_after in line.comments_after(leaf):
         for leaf in leaves:
             result.append(leaf, preformatted=True)
             for comment_after in line.comments_after(leaf):


@@ -1670,7 +1728,9 @@ def left_hand_split(line: Line, py36: bool = False) -> Iterator[Line]:
             yield result
 
 
             yield result
 
 

-def right_hand_split(line: Line, py36: bool = False) -> Iterator[Line]:
+def right_hand_split(
+    line: Line, py36: bool = False, omit: Collection[LeafID] = ()
+) -> Iterator[Line]:

     """Split line into many lines, starting with the last matching bracket pair."""
     head = Line(depth=line.depth)
     body = Line(depth=line.depth + 1, inside_brackets=True)
     """Split line into many lines, starting with the last matching bracket pair."""
     head = Line(depth=line.depth)
     body = Line(depth=line.depth + 1, inside_brackets=True)


@@ -1680,14 +1740,16 @@ def right_hand_split(line: Line, py36: bool = False) -> Iterator[Line]:
     head_leaves: List[Leaf] = []
     current_leaves = tail_leaves
     opening_bracket = None
     head_leaves: List[Leaf] = []
     current_leaves = tail_leaves
     opening_bracket = None

+    closing_bracket = None

     for leaf in reversed(line.leaves):
         if current_leaves is body_leaves:
             if leaf is opening_bracket:
                 current_leaves = head_leaves if body_leaves else tail_leaves
         current_leaves.append(leaf)
         if current_leaves is tail_leaves:
     for leaf in reversed(line.leaves):
         if current_leaves is body_leaves:
             if leaf is opening_bracket:
                 current_leaves = head_leaves if body_leaves else tail_leaves
         current_leaves.append(leaf)
         if current_leaves is tail_leaves:

-            if leaf.type in CLOSING_BRACKETS:
+            if leaf.type in CLOSING_BRACKETS and id(leaf) not in omit:

                 opening_bracket = leaf.opening_bracket
                 opening_bracket = leaf.opening_bracket

+                closing_bracket = leaf

                 current_leaves = body_leaves
     tail_leaves.reverse()
     body_leaves.reverse()
                 current_leaves = body_leaves
     tail_leaves.reverse()
     body_leaves.reverse()


@@ -1695,15 +1757,36 @@ def right_hand_split(line: Line, py36: bool = False) -> Iterator[Line]:
     # Since body is a new indent level, remove spurious leading whitespace.
     if body_leaves:
         normalize_prefix(body_leaves[0], inside_brackets=True)
     # Since body is a new indent level, remove spurious leading whitespace.
     if body_leaves:
         normalize_prefix(body_leaves[0], inside_brackets=True)

+    elif not head_leaves:
+        # No `head` and no `body` means the split failed. `tail` has all content.
+        raise CannotSplit("No brackets found")
+

     # Build the new lines.
     # Build the new lines.

-    for result, leaves in (
-        (head, head_leaves), (body, body_leaves), (tail, tail_leaves)
-    ):
+    for result, leaves in (head, head_leaves), (body, body_leaves), (tail, tail_leaves):

         for leaf in leaves:
             result.append(leaf, preformatted=True)
             for comment_after in line.comments_after(leaf):
                 result.append(comment_after, preformatted=True)
     bracket_split_succeeded_or_raise(head, body, tail)
         for leaf in leaves:
             result.append(leaf, preformatted=True)
             for comment_after in line.comments_after(leaf):
                 result.append(comment_after, preformatted=True)
     bracket_split_succeeded_or_raise(head, body, tail)

+    assert opening_bracket and closing_bracket
+    if (
+        opening_bracket.type == token.LPAR
+        and not opening_bracket.value
+        and closing_bracket.type == token.RPAR
+        and not closing_bracket.value
+    ):
+        # These parens were optional. If there aren't any delimiters or standalone
+        # comments in the body, they were unnecessary and another split without
+        # them should be attempted.
+        if not (
+            body.bracket_tracker.delimiters or line.contains_standalone_comments(0)
+        ):
+            omit = {id(closing_bracket), *omit}
+            yield from right_hand_split(line, py36=py36, omit=omit)
+            return
+
+    ensure_visible(opening_bracket)
+    ensure_visible(closing_bracket)

     for result in (head, body, tail):
         if result:
             yield result
     for result in (head, body, tail):
         if result:
             yield result


@@ -1817,12 +1900,7 @@ def delimiter_split(line: Line, py36: bool = False) -> Iterator[Line]:
 @dont_increase_indentation
 def standalone_comment_split(line: Line, py36: bool = False) -> Iterator[Line]:
     """Split standalone comments from the rest of the line."""
 @dont_increase_indentation
 def standalone_comment_split(line: Line, py36: bool = False) -> Iterator[Line]:
     """Split standalone comments from the rest of the line."""

-    for leaf in line.leaves:
-        if leaf.type == STANDALONE_COMMENT:
-            if leaf.bracket_depth == 0:
-                break
-
-    else:
+    if not line.contains_standalone_comments(0):

         raise CannotSplit("Line does not have any standalone comments")
 
     current_line = Line(depth=line.depth, inside_brackets=line.inside_brackets)
         raise CannotSplit("Line does not have any standalone comments")
 
     current_line = Line(depth=line.depth, inside_brackets=line.inside_brackets)


@@ -1905,10 +1983,24 @@ def normalize_string_quotes(leaf: Leaf) -> None:
     if first_quote_pos == -1:
         return  # There's an internal error
 
     if first_quote_pos == -1:
         return  # There's an internal error
 

+    prefix = leaf.value[:first_quote_pos]

     body = leaf.value[first_quote_pos + len(orig_quote):-len(orig_quote)]
     body = leaf.value[first_quote_pos + len(orig_quote):-len(orig_quote)]

-    new_body = body.replace(f"\\{orig_quote}", orig_quote).replace(
-        new_quote, f"\\{new_quote}"
-    )
+    unescaped_new_quote = re.compile(rf"(([^\\]|^)(\\\\)*){new_quote}")
+    escaped_orig_quote = re.compile(rf"\\(\\\\)*{orig_quote}")
+    if "r" in prefix.casefold():
+        if unescaped_new_quote.search(body):
+            # There's at least one unescaped new_quote in this raw string
+            # so converting is impossible
+            return
+
+        # Do not introduce or remove backslashes in raw strings
+        new_body = body
+    else:
+        new_body = escaped_orig_quote.sub(rf"\1{orig_quote}", body)
+        new_body = unescaped_new_quote.sub(rf"\1\\{new_quote}", new_body)
+        # Add escapes again for consecutive occurences of new_quote (sub
+        # doesn't match overlapping substrings).
+        new_body = unescaped_new_quote.sub(rf"\1\\{new_quote}", new_body)

     if new_quote == '"""' and new_body[-1] == '"':
         # edge case:
         new_body = new_body[:-1] + '\\"'
     if new_quote == '"""' and new_body[-1] == '"':
         # edge case:
         new_body = new_body[:-1] + '\\"'


@@ -1920,10 +2012,114 @@ def normalize_string_quotes(leaf: Leaf) -> None:
     if new_escape_count == orig_escape_count and orig_quote == '"':
         return  # Prefer double quotes
 
     if new_escape_count == orig_escape_count and orig_quote == '"':
         return  # Prefer double quotes
 

-    prefix = leaf.value[:first_quote_pos]

     leaf.value = f"{prefix}{new_quote}{new_body}{new_quote}"
 
 
     leaf.value = f"{prefix}{new_quote}{new_body}{new_quote}"
 
 

+def normalize_invisible_parens(node: Node, parens_after: Set[str]) -> None:
+    """Make existing optional parentheses invisible or create new ones.
+
+    Standardizes on visible parentheses for single-element tuples, and keeps
+    existing visible parentheses for other tuples and generator expressions.
+    """
+    check_lpar = False
+    for child in list(node.children):
+        if check_lpar:
+            if child.type == syms.atom:
+                if not (
+                    is_empty_tuple(child)
+                    or is_one_tuple(child)
+                    or max_delimiter_priority_in_atom(child) >= COMMA_PRIORITY
+                ):
+                    first = child.children[0]
+                    last = child.children[-1]
+                    if first.type == token.LPAR and last.type == token.RPAR:
+                        # make parentheses invisible
+                        first.value = ""  # type: ignore
+                        last.value = ""  # type: ignore
+            elif is_one_tuple(child):
+                # wrap child in visible parentheses
+                lpar = Leaf(token.LPAR, "(")
+                rpar = Leaf(token.RPAR, ")")
+                index = child.remove() or 0
+                node.insert_child(index, Node(syms.atom, [lpar, child, rpar]))
+            else:
+                # wrap child in invisible parentheses
+                lpar = Leaf(token.LPAR, "")
+                rpar = Leaf(token.RPAR, "")
+                index = child.remove() or 0
+                node.insert_child(index, Node(syms.atom, [lpar, child, rpar]))
+
+        check_lpar = isinstance(child, Leaf) and child.value in parens_after
+
+
+def is_empty_tuple(node: LN) -> bool:
+    """Return True if `node` holds an empty tuple."""
+    return (
+        node.type == syms.atom
+        and len(node.children) == 2
+        and node.children[0].type == token.LPAR
+        and node.children[1].type == token.RPAR
+    )
+
+
+def is_one_tuple(node: LN) -> bool:
+    """Return True if `node` holds a tuple with one element, with or without parens."""
+    if node.type == syms.atom:
+        if len(node.children) != 3:
+            return False
+
+        lpar, gexp, rpar = node.children
+        if not (
+            lpar.type == token.LPAR
+            and gexp.type == syms.testlist_gexp
+            and rpar.type == token.RPAR
+        ):
+            return False
+
+        return len(gexp.children) == 2 and gexp.children[1].type == token.COMMA
+
+    return (
+        node.type in IMPLICIT_TUPLE
+        and len(node.children) == 2
+        and node.children[1].type == token.COMMA
+    )
+
+
+def max_delimiter_priority_in_atom(node: LN) -> int:
+    if node.type != syms.atom:
+        return 0
+
+    first = node.children[0]
+    last = node.children[-1]
+    if not (first.type == token.LPAR and last.type == token.RPAR):
+        return 0
+
+    bt = BracketTracker()
+    for c in node.children[1:-1]:
+        if isinstance(c, Leaf):
+            bt.mark(c)
+        else:
+            for leaf in c.leaves():
+                bt.mark(leaf)
+    try:
+        return bt.max_delimiter_priority()
+
+    except ValueError:
+        return 0
+
+
+def ensure_visible(leaf: Leaf) -> None:
+    """Make sure parentheses are visible.
+
+    They could be invisible as part of some statements (see
+    :func:`normalize_invible_parens` and :func:`visit_import_from`).
+    """
+    if leaf.type == token.LPAR:
+        leaf.value = "("
+    elif leaf.type == token.RPAR:
+        leaf.value = ")"
+
+

 def is_python36(node: Node) -> bool:
     """Return True if the current file is using Python 3.6+ features.
 
 def is_python36(node: Node) -> bool:
     """Return True if the current file is using Python 3.6+ features.
 


@@ -1974,6 +2170,7 @@ def gen_python_files_in_dir(path: Path) -> Iterator[Path]:
 class Report:
     """Provides a reformatting counter. Can be rendered with `str(report)`."""
     check: bool = False
 class Report:
     """Provides a reformatting counter. Can be rendered with `str(report)`."""
     check: bool = False

+    quiet: bool = False

     change_count: int = 0
     same_count: int = 0
     failure_count: int = 0
     change_count: int = 0
     same_count: int = 0
     failure_count: int = 0


@@ -1982,10 +2179,12 @@ class Report:
         """Increment the counter for successful reformatting. Write out a message."""
         if changed:
             reformatted = "would reformat" if self.check else "reformatted"
         """Increment the counter for successful reformatting. Write out a message."""
         if changed:
             reformatted = "would reformat" if self.check else "reformatted"

-            out(f"{reformatted} {src}")
+            if not self.quiet:
+                out(f"{reformatted} {src}")

             self.change_count += 1
         else:
             self.change_count += 1
         else:

-            out(f"{src} already well formatted, good job.", bold=False)
+            if not self.quiet:
+                out(f"{src} already well formatted, good job.", bold=False)

             self.same_count += 1
 
     def failed(self, src: Path, message: str) -> None:
             self.same_count += 1
 
     def failed(self, src: Path, message: str) -> None: