Use nullcontext in case when lock is None. Shutdown pool after code formatting. ...

[etc/vim.git] / black.py

diff --git a/black.py b/black.py
index 7bfcfca874ffd7bcdeae9fed15aa082cf325b549..952fb0c659ff2a9a4969efc5506e37f504a31f43 100644 (file)
--- a/black.py
+++ b/black.py
@@ -1,6 +1,6 @@
 import asyncio
 import asyncio

-from asyncio.base_events import BaseEventLoop

 from concurrent.futures import Executor, ProcessPoolExecutor
 from concurrent.futures import Executor, ProcessPoolExecutor

+from contextlib import contextmanager

 from datetime import datetime
 from enum import Enum
 from functools import lru_cache, partial, wraps
 from datetime import datetime
 from enum import Enum
 from functools import lru_cache, partial, wraps


@@ -16,6 +16,7 @@ import signal
 import sys
 import tempfile
 import tokenize
 import sys
 import tempfile
 import tokenize

+import traceback

 from typing import (
     Any,
     Callable,
 from typing import (
     Any,
     Callable,


@@ -40,6 +41,7 @@ from appdirs import user_cache_dir
 from attr import dataclass, evolve, Factory
 import click
 import toml
 from attr import dataclass, evolve, Factory
 import click
 import toml

+from typed_ast import ast3, ast27

 
 # lib2to3 fork
 from blib2to3.pytree import Node, Leaf, type_repr
 
 # lib2to3 fork
 from blib2to3.pytree import Node, Leaf, type_repr


@@ -135,19 +137,28 @@ class Feature(Enum):
     NUMERIC_UNDERSCORES = 3
     TRAILING_COMMA_IN_CALL = 4
     TRAILING_COMMA_IN_DEF = 5
     NUMERIC_UNDERSCORES = 3
     TRAILING_COMMA_IN_CALL = 4
     TRAILING_COMMA_IN_DEF = 5

+    # The following two feature-flags are mutually exclusive, and exactly one should be
+    # set for every version of python.
+    ASYNC_IDENTIFIERS = 6
+    ASYNC_KEYWORDS = 7

 
 
 VERSION_TO_FEATURES: Dict[TargetVersion, Set[Feature]] = {
 
 
 VERSION_TO_FEATURES: Dict[TargetVersion, Set[Feature]] = {

-    TargetVersion.PY27: set(),
-    TargetVersion.PY33: {Feature.UNICODE_LITERALS},
-    TargetVersion.PY34: {Feature.UNICODE_LITERALS},
-    TargetVersion.PY35: {Feature.UNICODE_LITERALS, Feature.TRAILING_COMMA_IN_CALL},
+    TargetVersion.PY27: {Feature.ASYNC_IDENTIFIERS},
+    TargetVersion.PY33: {Feature.UNICODE_LITERALS, Feature.ASYNC_IDENTIFIERS},
+    TargetVersion.PY34: {Feature.UNICODE_LITERALS, Feature.ASYNC_IDENTIFIERS},
+    TargetVersion.PY35: {
+        Feature.UNICODE_LITERALS,
+        Feature.TRAILING_COMMA_IN_CALL,
+        Feature.ASYNC_IDENTIFIERS,
+    },

     TargetVersion.PY36: {
         Feature.UNICODE_LITERALS,
         Feature.F_STRINGS,
         Feature.NUMERIC_UNDERSCORES,
         Feature.TRAILING_COMMA_IN_CALL,
         Feature.TRAILING_COMMA_IN_DEF,
     TargetVersion.PY36: {
         Feature.UNICODE_LITERALS,
         Feature.F_STRINGS,
         Feature.NUMERIC_UNDERSCORES,
         Feature.TRAILING_COMMA_IN_CALL,
         Feature.TRAILING_COMMA_IN_DEF,

+        Feature.ASYNC_IDENTIFIERS,

     },
     TargetVersion.PY37: {
         Feature.UNICODE_LITERALS,
     },
     TargetVersion.PY37: {
         Feature.UNICODE_LITERALS,


@@ -155,6 +166,7 @@ VERSION_TO_FEATURES: Dict[TargetVersion, Set[Feature]] = {
         Feature.NUMERIC_UNDERSCORES,
         Feature.TRAILING_COMMA_IN_CALL,
         Feature.TRAILING_COMMA_IN_DEF,
         Feature.NUMERIC_UNDERSCORES,
         Feature.TRAILING_COMMA_IN_CALL,
         Feature.TRAILING_COMMA_IN_DEF,

+        Feature.ASYNC_KEYWORDS,

     },
     TargetVersion.PY38: {
         Feature.UNICODE_LITERALS,
     },
     TargetVersion.PY38: {
         Feature.UNICODE_LITERALS,


@@ -162,6 +174,7 @@ VERSION_TO_FEATURES: Dict[TargetVersion, Set[Feature]] = {
         Feature.NUMERIC_UNDERSCORES,
         Feature.TRAILING_COMMA_IN_CALL,
         Feature.TRAILING_COMMA_IN_DEF,
         Feature.NUMERIC_UNDERSCORES,
         Feature.TRAILING_COMMA_IN_CALL,
         Feature.TRAILING_COMMA_IN_DEF,

+        Feature.ASYNC_KEYWORDS,

     },
 }
 
     },
 }
 


@@ -231,6 +244,7 @@ def read_pyproject_toml(
 
 
 @click.command(context_settings=dict(help_option_names=["-h", "--help"]))
 
 
 @click.command(context_settings=dict(help_option_names=["-h", "--help"]))

+@click.option("-c", "--code", type=str, help="Format the code passed in as a string.")

 @click.option(
     "-l",
     "--line-length",
 @click.option(
     "-l",
     "--line-length",


@@ -323,7 +337,7 @@ def read_pyproject_toml(
     "--quiet",
     is_flag=True,
     help=(
     "--quiet",
     is_flag=True,
     help=(

-        "Don't emit non-error messages to stderr. Errors are still emitted, "
+        "Don't emit non-error messages to stderr. Errors are still emitted; "

         "silence those with 2>/dev/null."
     ),
 )
         "silence those with 2>/dev/null."
     ),
 )


@@ -357,6 +371,7 @@ def read_pyproject_toml(
 @click.pass_context
 def main(
     ctx: click.Context,
 @click.pass_context
 def main(
     ctx: click.Context,

+    code: Optional[str],

     line_length: int,
     target_version: List[TargetVersion],
     check: bool,
     line_length: int,
     target_version: List[TargetVersion],
     check: bool,


@@ -397,6 +412,9 @@ def main(
     )
     if config and verbose:
         out(f"Using configuration from {config}.", bold=False, fg="blue")
     )
     if config and verbose:
         out(f"Using configuration from {config}.", bold=False, fg="blue")

+    if code is not None:
+        print(format_str(code, mode=mode))
+        ctx.exit(0)

     try:
         include_regex = re_compile_maybe_verbose(include)
     except re.error:
     try:
         include_regex = re_compile_maybe_verbose(include)
     except re.error:


@@ -435,25 +453,12 @@ def main(
             report=report,
         )
     else:
             report=report,
         )
     else:

-        loop = asyncio.get_event_loop()
-        executor = ProcessPoolExecutor(max_workers=os.cpu_count())
-        try:
-            loop.run_until_complete(
-                schedule_formatting(
-                    sources=sources,
-                    fast=fast,
-                    write_back=write_back,
-                    mode=mode,
-                    report=report,
-                    loop=loop,
-                    executor=executor,
-                )
-            )
-        finally:
-            shutdown(loop)
+        reformat_many(
+            sources=sources, fast=fast, write_back=write_back, mode=mode, report=report
+        )
+

     if verbose or not quiet:
     if verbose or not quiet:

-        bang = "💥 💔 💥" if report.return_code else "✨ 🍰 ✨"
-        out(f"All done! {bang}")
+        out("Oh no! 💥 💔 💥" if report.return_code else "All done! ✨ 🍰 ✨")

         click.secho(str(report), err=True)
     ctx.exit(report.return_code)
 
         click.secho(str(report), err=True)
     ctx.exit(report.return_code)
 


@@ -463,8 +468,7 @@ def reformat_one(
 ) -> None:
     """Reformat a single file under `src` without spawning child processes.
 
 ) -> None:
     """Reformat a single file under `src` without spawning child processes.
 

-    If `quiet` is True, non-error messages are not output. `line_length`,
-    `write_back`, `fast` and `pyi` options are passed to
+    `fast`, `write_back`, and `mode` options are passed to

     :func:`format_file_in_place` or :func:`format_stdin_to_stdout`.
     """
     try:
     :func:`format_file_in_place` or :func:`format_stdin_to_stdout`.
     """
     try:


@@ -492,20 +496,51 @@ def reformat_one(
         report.failed(src, str(exc))
 
 
         report.failed(src, str(exc))
 
 

+def reformat_many(
+    sources: Set[Path],
+    fast: bool,
+    write_back: WriteBack,
+    mode: FileMode,
+    report: "Report",
+) -> None:
+    """Reformat multiple files using a ProcessPoolExecutor."""
+    loop = asyncio.get_event_loop()
+    worker_count = os.cpu_count()
+    if sys.platform == "win32":
+        # Work around https://bugs.python.org/issue26903
+        worker_count = min(worker_count, 61)
+    executor = ProcessPoolExecutor(max_workers=worker_count)
+    try:
+        loop.run_until_complete(
+            schedule_formatting(
+                sources=sources,
+                fast=fast,
+                write_back=write_back,
+                mode=mode,
+                report=report,
+                loop=loop,
+                executor=executor,
+            )
+        )
+    finally:
+        shutdown(loop)
+        executor.shutdown()
+
+

 async def schedule_formatting(
     sources: Set[Path],
     fast: bool,
     write_back: WriteBack,
     mode: FileMode,
     report: "Report",
 async def schedule_formatting(
     sources: Set[Path],
     fast: bool,
     write_back: WriteBack,
     mode: FileMode,
     report: "Report",

-    loop: BaseEventLoop,
+    loop: asyncio.AbstractEventLoop,

     executor: Executor,
 ) -> None:
     """Run formatting of `sources` in parallel using the provided `executor`.
 
     (Use ProcessPoolExecutors for actual parallelism.)
 
     executor: Executor,
 ) -> None:
     """Run formatting of `sources` in parallel using the provided `executor`.
 
     (Use ProcessPoolExecutors for actual parallelism.)
 

-    `line_length`, `write_back`, `fast`, and `pyi` options are passed to
+    `write_back`, `fast`, and `mode` options are passed to

     :func:`format_file_in_place`.
     """
     cache: Cache = {}
     :func:`format_file_in_place`.
     """
     cache: Cache = {}


@@ -574,7 +609,7 @@ def format_file_in_place(
 
     If `write_back` is DIFF, write a diff to stdout. If it is YES, write reformatted
     code to the file.
 
     If `write_back` is DIFF, write a diff to stdout. If it is YES, write reformatted
     code to the file.

-    `line_length` and `fast` options are passed to :func:`format_file_contents`.
+    `mode` and `fast` options are passed to :func:`format_file_contents`.

     """
     if src.suffix == ".pyi":
         mode = evolve(mode, is_pyi=True)
     """
     if src.suffix == ".pyi":
         mode = evolve(mode, is_pyi=True)


@@ -595,9 +630,8 @@ def format_file_in_place(
         src_name = f"{src}\t{then} +0000"
         dst_name = f"{src}\t{now} +0000"
         diff_contents = diff(src_contents, dst_contents, src_name, dst_name)
         src_name = f"{src}\t{then} +0000"
         dst_name = f"{src}\t{now} +0000"
         diff_contents = diff(src_contents, dst_contents, src_name, dst_name)

-        if lock:
-            lock.acquire()
-        try:
+
+        with lock or nullcontext():

             f = io.TextIOWrapper(
                 sys.stdout.buffer,
                 encoding=encoding,
             f = io.TextIOWrapper(
                 sys.stdout.buffer,
                 encoding=encoding,


@@ -606,9 +640,7 @@ def format_file_in_place(
             )
             f.write(diff_contents)
             f.detach()
             )
             f.write(diff_contents)
             f.detach()

-        finally:
-            if lock:
-                lock.release()
+

     return True
 
 
     return True
 
 


@@ -652,7 +684,7 @@ def format_file_contents(
 
     If `fast` is False, additionally confirm that the reformatted code is
     valid by calling :func:`assert_equivalent` and :func:`assert_stable` on it.
 
     If `fast` is False, additionally confirm that the reformatted code is
     valid by calling :func:`assert_equivalent` and :func:`assert_stable` on it.

-    `line_length` is passed to :func:`format_str`.
+    `mode` is passed to :func:`format_str`.

     """
     if src_contents.strip() == "":
         raise NothingChanged
     """
     if src_contents.strip() == "":
         raise NothingChanged


@@ -670,10 +702,11 @@ def format_file_contents(
 def format_str(src_contents: str, *, mode: FileMode) -> FileContent:
     """Reformat a string and return new contents.
 
 def format_str(src_contents: str, *, mode: FileMode) -> FileContent:
     """Reformat a string and return new contents.
 

-    `line_length` determines how many characters per line are allowed.
+    `mode` determines formatting options, such as how many characters per line are
+    allowed.

     """
     src_node = lib2to3_parse(src_contents.lstrip(), mode.target_versions)
     """
     src_node = lib2to3_parse(src_contents.lstrip(), mode.target_versions)

-    dst_contents = ""
+    dst_contents = []

     future_imports = get_future_imports(src_node)
     if mode.target_versions:
         versions = mode.target_versions
     future_imports = get_future_imports(src_node)
     if mode.target_versions:
         versions = mode.target_versions


@@ -696,15 +729,15 @@ def format_str(src_contents: str, *, mode: FileMode) -> FileContent:
     }
     for current_line in lines.visit(src_node):
         for _ in range(after):
     }
     for current_line in lines.visit(src_node):
         for _ in range(after):

-            dst_contents += str(empty_line)
+            dst_contents.append(str(empty_line))

         before, after = elt.maybe_empty_lines(current_line)
         for _ in range(before):
         before, after = elt.maybe_empty_lines(current_line)
         for _ in range(before):

-            dst_contents += str(empty_line)
+            dst_contents.append(str(empty_line))

         for line in split_line(
             current_line, line_length=mode.line_length, features=split_line_features
         ):
         for line in split_line(
             current_line, line_length=mode.line_length, features=split_line_features
         ):

-            dst_contents += str(line)
-    return dst_contents
+            dst_contents.append(str(line))
+    return "".join(dst_contents)

 
 
 def decode_bytes(src: bytes) -> Tuple[FileContent, Encoding, NewLine]:
 
 
 def decode_bytes(src: bytes) -> Tuple[FileContent, Encoding, NewLine]:


@@ -728,16 +761,38 @@ def get_grammars(target_versions: Set[TargetVersion]) -> List[Grammar]:
     if not target_versions:
         # No target_version specified, so try all grammars.
         return [
     if not target_versions:
         # No target_version specified, so try all grammars.
         return [

+            # Python 3.7+
+            pygram.python_grammar_no_print_statement_no_exec_statement_async_keywords,
+            # Python 3.0-3.6

             pygram.python_grammar_no_print_statement_no_exec_statement,
             pygram.python_grammar_no_print_statement_no_exec_statement,

+            # Python 2.7 with future print_function import

             pygram.python_grammar_no_print_statement,
             pygram.python_grammar_no_print_statement,

+            # Python 2.7

             pygram.python_grammar,
         ]
     elif all(version.is_python2() for version in target_versions):
         # Python 2-only code, so try Python 2 grammars.
             pygram.python_grammar,
         ]
     elif all(version.is_python2() for version in target_versions):
         # Python 2-only code, so try Python 2 grammars.

-        return [pygram.python_grammar_no_print_statement, pygram.python_grammar]
+        return [
+            # Python 2.7 with future print_function import
+            pygram.python_grammar_no_print_statement,
+            # Python 2.7
+            pygram.python_grammar,
+        ]

     else:
         # Python 3-compatible code, so only try Python 3 grammar.
     else:
         # Python 3-compatible code, so only try Python 3 grammar.

-        return [pygram.python_grammar_no_print_statement_no_exec_statement]
+        grammars = []
+        # If we have to parse both, try to parse async as a keyword first
+        if not supports_feature(target_versions, Feature.ASYNC_IDENTIFIERS):
+            # Python 3.7+
+            grammars.append(
+                pygram.python_grammar_no_print_statement_no_exec_statement_async_keywords  # noqa: B950
+            )
+        if not supports_feature(target_versions, Feature.ASYNC_KEYWORDS):
+            # Python 3.0-3.6
+            grammars.append(pygram.python_grammar_no_print_statement_no_exec_statement)
+        # At least one of the above branches must have been taken, because every Python
+        # version has exactly one of the two 'ASYNC_*' flags
+        return grammars

 
 
 def lib2to3_parse(src_txt: str, target_versions: Iterable[TargetVersion] = ()) -> Node:
 
 
 def lib2to3_parse(src_txt: str, target_versions: Iterable[TargetVersion] = ()) -> Node:


@@ -1004,7 +1059,7 @@ class BracketTracker:
         """Return True if there is an yet unmatched open bracket on the line."""
         return bool(self.bracket_match)
 
         """Return True if there is an yet unmatched open bracket on the line."""
         return bool(self.bracket_match)
 

-    def max_delimiter_priority(self, exclude: Iterable[LeafID] = ()) -> int:
+    def max_delimiter_priority(self, exclude: Iterable[LeafID] = ()) -> Priority:

         """Return the highest priority of a delimiter found on the line.
 
         Values are consistent with what `is_split_*_delimiter()` return.
         """Return the highest priority of a delimiter found on the line.
 
         Values are consistent with what `is_split_*_delimiter()` return.


@@ -1012,7 +1067,7 @@ class BracketTracker:
         """
         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)
 

-    def delimiter_count_with_priority(self, priority: int = 0) -> int:
+    def delimiter_count_with_priority(self, priority: Priority = 0) -> int:

         """Return the number of delimiters with the given `priority`.
 
         If no `priority` is passed, defaults to max priority on the line.
         """Return the number of delimiters with the given `priority`.
 
         If no `priority` is passed, defaults to max priority on the line.


@@ -1225,10 +1280,13 @@ class Line:
         try:
             last_leaf = self.leaves[-1]
             ignored_ids.add(id(last_leaf))
         try:
             last_leaf = self.leaves[-1]
             ignored_ids.add(id(last_leaf))

-            if last_leaf.type == token.COMMA:
-                # When trailing commas are inserted by Black for consistency, comments
-                # after the previous last element are not moved (they don't have to,
-                # rendering will still be correct).  So we ignore trailing commas.
+            if last_leaf.type == token.COMMA or (
+                last_leaf.type == token.RPAR and not last_leaf.value
+            ):
+                # When trailing commas or optional parens are inserted by Black for
+                # consistency, comments after the previous last element are not moved
+                # (they don't have to, rendering will still be correct).  So we ignore
+                # trailing commas and invisible.

                 last_leaf = self.leaves[-2]
                 ignored_ids.add(id(last_leaf))
         except IndexError:
                 last_leaf = self.leaves[-2]
                 ignored_ids.add(id(last_leaf))
         except IndexError:


@@ -1295,7 +1353,10 @@ class Line:
             bracket_depth = leaf.bracket_depth
             if bracket_depth == depth and leaf.type == token.COMMA:
                 commas += 1
             bracket_depth = leaf.bracket_depth
             if bracket_depth == depth and leaf.type == token.COMMA:
                 commas += 1

-                if leaf.parent and leaf.parent.type == syms.arglist:
+                if leaf.parent and leaf.parent.type in {
+                    syms.arglist,
+                    syms.typedargslist,
+                }:

                     commas += 1
                     break
 
                     commas += 1
                     break
 


@@ -1322,7 +1383,23 @@ class Line:
             comment.prefix = ""
             return False
 
             comment.prefix = ""
             return False
 

-        self.comments.setdefault(id(self.leaves[-1]), []).append(comment)
+        last_leaf = self.leaves[-1]
+        if (
+            last_leaf.type == token.RPAR
+            and not last_leaf.value
+            and last_leaf.parent
+            and len(list(last_leaf.parent.leaves())) <= 3
+            and not is_type_comment(comment)
+        ):
+            # Comments on an optional parens wrapping a single leaf should belong to
+            # the wrapped node except if it's a type comment. Pinning the comment like
+            # this avoids unstable formatting caused by comment migration.
+            if len(self.leaves) < 2:
+                comment.type = STANDALONE_COMMENT
+                comment.prefix = ""
+                return False
+            last_leaf = self.leaves[-2]
+        self.comments.setdefault(id(last_leaf), []).append(comment)

         return True
 
     def comments_after(self, leaf: Leaf) -> List[Leaf]:
         return True
 
     def comments_after(self, leaf: Leaf) -> List[Leaf]:


@@ -1545,6 +1622,39 @@ class LineGenerator(Visitor[Line]):
                 self.current_line.append(node)
         yield from super().visit_default(node)
 
                 self.current_line.append(node)
         yield from super().visit_default(node)
 

+    def visit_atom(self, node: Node) -> Iterator[Line]:
+        # Always make parentheses invisible around a single node, because it should
+        # not be needed (except in the case of yield, where removing the parentheses
+        # produces a SyntaxError).
+        if (
+            len(node.children) == 3
+            and isinstance(node.children[0], Leaf)
+            and node.children[0].type == token.LPAR
+            and isinstance(node.children[2], Leaf)
+            and node.children[2].type == token.RPAR
+            and isinstance(node.children[1], Leaf)
+            and not (
+                node.children[1].type == token.NAME
+                and node.children[1].value == "yield"
+            )
+        ):
+            node.children[0].value = ""
+            node.children[2].value = ""
+        yield from super().visit_default(node)
+
+    def visit_factor(self, node: Node) -> Iterator[Line]:
+        """Force parentheses between a unary op and a binary power:
+
+        -2 ** 8 -> -(2 ** 8)
+        """
+        child = node.children[1]
+        if child.type == syms.power and len(child.children) == 3:
+            lpar = Leaf(token.LPAR, "(")
+            rpar = Leaf(token.RPAR, ")")
+            index = child.remove() or 0
+            node.insert_child(index, Node(syms.atom, [lpar, child, rpar]))
+        yield from self.visit_default(node)
+

     def visit_INDENT(self, node: Node) -> Iterator[Line]:
         """Increase indentation level, maybe yield a line."""
         # In blib2to3 INDENT never holds comments.
     def visit_INDENT(self, node: Node) -> Iterator[Line]:
         """Increase indentation level, maybe yield a line."""
         # In blib2to3 INDENT never holds comments.


@@ -1958,7 +2068,7 @@ def container_of(leaf: Leaf) -> LN:
     return container
 
 
     return container
 
 

-def is_split_after_delimiter(leaf: Leaf, previous: Optional[Leaf] = None) -> int:
+def is_split_after_delimiter(leaf: Leaf, previous: Optional[Leaf] = None) -> Priority:

     """Return the priority of the `leaf` delimiter, given a line break after it.
 
     The delimiter priorities returned here are from those delimiters that would
     """Return the priority of the `leaf` delimiter, given a line break after it.
 
     The delimiter priorities returned here are from those delimiters that would


@@ -1972,7 +2082,7 @@ def is_split_after_delimiter(leaf: Leaf, previous: Optional[Leaf] = None) -> int
     return 0
 
 
     return 0
 
 

-def is_split_before_delimiter(leaf: Leaf, previous: Optional[Leaf] = None) -> int:
+def is_split_before_delimiter(leaf: Leaf, previous: Optional[Leaf] = None) -> Priority:

     """Return the priority of the `leaf` delimiter, given a line break before it.
 
     The delimiter priorities returned here are from those delimiters that would
     """Return the priority of the `leaf` delimiter, given a line break before it.
 
     The delimiter priorities returned here are from those delimiters that would


@@ -2122,15 +2232,21 @@ def list_comments(prefix: str, *, is_endmarker: bool) -> List[ProtoComment]:
 
     consumed = 0
     nlines = 0
 
     consumed = 0
     nlines = 0

+    ignored_lines = 0

     for index, line in enumerate(prefix.split("\n")):
         consumed += len(line) + 1  # adding the length of the split '\n'
         line = line.lstrip()
         if not line:
             nlines += 1
         if not line.startswith("#"):
     for index, line in enumerate(prefix.split("\n")):
         consumed += len(line) + 1  # adding the length of the split '\n'
         line = line.lstrip()
         if not line:
             nlines += 1
         if not line.startswith("#"):

+            # Escaped newlines outside of a comment are not really newlines at
+            # all. We treat a single-line comment following an escaped newline
+            # as a simple trailing comment.
+            if line.endswith("\\"):
+                ignored_lines += 1

             continue
 
             continue
 

-        if index == 0 and not is_endmarker:
+        if index == ignored_lines and not is_endmarker:

             comment_type = token.COMMENT  # simple trailing comment
         else:
             comment_type = STANDALONE_COMMENT
             comment_type = token.COMMENT  # simple trailing comment
         else:
             comment_type = STANDALONE_COMMENT


@@ -2405,9 +2521,13 @@ def bracket_split_build_line(
         if leaves:
             # Since body is a new indent level, remove spurious leading whitespace.
             normalize_prefix(leaves[0], inside_brackets=True)
         if leaves:
             # Since body is a new indent level, remove spurious leading whitespace.
             normalize_prefix(leaves[0], inside_brackets=True)

-            # Ensure a trailing comma for imports, but be careful not to add one after
-            # any comments.
-            if original.is_import:
+            # Ensure a trailing comma for imports and standalone function arguments, but
+            # be careful not to add one after any comments.
+            no_commas = original.is_def and not any(
+                l.type == token.COMMA for l in leaves
+            )
+
+            if original.is_import or no_commas:

                 for i in range(len(leaves) - 1, -1, -1):
                     if leaves[i].type == STANDALONE_COMMENT:
                         continue
                 for i in range(len(leaves) - 1, -1, -1):
                     if leaves[i].type == STANDALONE_COMMENT:
                         continue


@@ -2646,7 +2766,15 @@ def normalize_string_quotes(leaf: Leaf) -> None:
         new_body = sub_twice(escaped_orig_quote, rf"\1\2{orig_quote}", new_body)
         new_body = sub_twice(unescaped_new_quote, rf"\1\\{new_quote}", new_body)
     if "f" in prefix.casefold():
         new_body = sub_twice(escaped_orig_quote, rf"\1\2{orig_quote}", new_body)
         new_body = sub_twice(unescaped_new_quote, rf"\1\\{new_quote}", new_body)
     if "f" in prefix.casefold():

-        matches = re.findall(r"[^{]\{(.*?)\}[^}]", new_body)
+        matches = re.findall(
+            r"""
+            (?:[^{]|^)\{  # start of the string or a non-{ followed by a single {
+                ([^{].*?)  # contents of the brackets except if begins with {{
+            \}(?:[^}]|$)  # A } followed by end of the string or a non-}
+            """,
+            new_body,
+            re.VERBOSE,
+        )

         for m in matches:
             if "\\" in str(m):
                 # Do not introduce backslashes in interpolated expressions
         for m in matches:
             if "\\" in str(m):
                 # Do not introduce backslashes in interpolated expressions


@@ -2713,7 +2841,7 @@ def format_float_or_int_string(text: str) -> str:
 def normalize_invisible_parens(node: Node, parens_after: Set[str]) -> None:
     """Make existing optional parentheses invisible or create new ones.
 
 def normalize_invisible_parens(node: Node, parens_after: Set[str]) -> None:
     """Make existing optional parentheses invisible or create new ones.
 

-    `parens_after` is a set of string leaf values immeditely after which parens
+    `parens_after` is a set of string leaf values immediately after which parens

     should be put.
 
     Standardizes on visible parentheses for single-element tuples, and keeps
     should be put.
 
     Standardizes on visible parentheses for single-element tuples, and keeps


@@ -2991,7 +3119,7 @@ def is_stub_body(node: LN) -> bool:
     )
 
 
     )
 
 

-def max_delimiter_priority_in_atom(node: LN) -> int:
+def max_delimiter_priority_in_atom(node: LN) -> Priority:

     """Return maximum delimiter priority inside `node`.
 
     This is specific to atoms with contents contained in a pair of parentheses.
     """Return maximum delimiter priority inside `node`.
 
     This is specific to atoms with contents contained in a pair of parentheses.


@@ -3023,7 +3151,7 @@ def ensure_visible(leaf: Leaf) -> None:
     """Make sure parentheses are visible.
 
     They could be invisible as part of some statements (see
     """Make sure parentheses are visible.
 
     They could be invisible as part of some statements (see

-    :func:`normalize_invible_parens` and :func:`visit_import_from`).
+    :func:`normalize_invisible_parens` and :func:`visit_import_from`).

     """
     if leaf.type == token.LPAR:
         leaf.value = "("
     """
     if leaf.type == token.LPAR:
         leaf.value = "("


@@ -3351,17 +3479,32 @@ class Report:
         return ", ".join(report) + "."
 
 
         return ", ".join(report) + "."
 
 

+def parse_ast(src: str) -> Union[ast3.AST, ast27.AST]:
+    for feature_version in (7, 6):
+        try:
+            return ast3.parse(src, feature_version=feature_version)
+        except SyntaxError:
+            continue
+
+    return ast27.parse(src)
+
+

 def assert_equivalent(src: str, dst: str) -> None:
     """Raise AssertionError if `src` and `dst` aren't equivalent."""
 
 def assert_equivalent(src: str, dst: str) -> None:
     """Raise AssertionError if `src` and `dst` aren't equivalent."""
 

-    import ast
-    import traceback
-
-    def _v(node: ast.AST, depth: int = 0) -> Iterator[str]:
+    def _v(node: Union[ast3.AST, ast27.AST], depth: int = 0) -> Iterator[str]:

         """Simple visitor generating strings to compare ASTs by content."""
         yield f"{'  ' * depth}{node.__class__.__name__}("
 
         for field in sorted(node._fields):
         """Simple visitor generating strings to compare ASTs by content."""
         yield f"{'  ' * depth}{node.__class__.__name__}("
 
         for field in sorted(node._fields):

+            # TypeIgnore has only one field 'lineno' which breaks this comparison
+            if isinstance(node, (ast3.TypeIgnore, ast27.TypeIgnore)):
+                break
+
+            # Ignore str kind which is case sensitive / and ignores unicode_literals
+            if isinstance(node, (ast3.Str, ast27.Str, ast3.Bytes)) and field == "kind":
+                continue
+

             try:
                 value = getattr(node, field)
             except AttributeError:
             try:
                 value = getattr(node, field)
             except AttributeError:


@@ -3375,15 +3518,15 @@ def assert_equivalent(src: str, dst: str) -> None:
                     # parentheses and they change the AST.
                     if (
                         field == "targets"
                     # parentheses and they change the AST.
                     if (
                         field == "targets"

-                        and isinstance(node, ast.Delete)
-                        and isinstance(item, ast.Tuple)
+                        and isinstance(node, (ast3.Delete, ast27.Delete))
+                        and isinstance(item, (ast3.Tuple, ast27.Tuple))

                     ):
                         for item in item.elts:
                             yield from _v(item, depth + 2)
                     ):
                         for item in item.elts:
                             yield from _v(item, depth + 2)

-                    elif isinstance(item, ast.AST):
+                    elif isinstance(item, (ast3.AST, ast27.AST)):

                         yield from _v(item, depth + 2)
 
                         yield from _v(item, depth + 2)
 

-            elif isinstance(value, ast.AST):
+            elif isinstance(value, (ast3.AST, ast27.AST)):

                 yield from _v(value, depth + 2)
 
             else:
                 yield from _v(value, depth + 2)
 
             else:


@@ -3392,17 +3535,15 @@ def assert_equivalent(src: str, dst: str) -> None:
         yield f"{'  ' * depth})  # /{node.__class__.__name__}"
 
     try:
         yield f"{'  ' * depth})  # /{node.__class__.__name__}"
 
     try:

-        src_ast = ast.parse(src)
+        src_ast = parse_ast(src)

     except Exception as exc:
     except Exception as exc:

-        major, minor = sys.version_info[:2]

         raise AssertionError(
         raise AssertionError(

-            f"cannot use --safe with this file; failed to parse source file "
-            f"with Python {major}.{minor}'s builtin AST. Re-run with --fast "
-            f"or stop using deprecated Python 2 syntax. AST error message: {exc}"
+            f"cannot use --safe with this file; failed to parse source file.  "
+            f"AST error message: {exc}"

         )
 
     try:
         )
 
     try:

-        dst_ast = ast.parse(dst)
+        dst_ast = parse_ast(dst)

     except Exception as exc:
         log = dump_to_file("".join(traceback.format_tb(exc.__traceback__)), dst)
         raise AssertionError(
     except Exception as exc:
         log = dump_to_file("".join(traceback.format_tb(exc.__traceback__)), dst)
         raise AssertionError(


@@ -3441,8 +3582,6 @@ def assert_stable(src: str, dst: str, mode: FileMode) -> None:
 
 def dump_to_file(*output: str) -> str:
     """Dump `output` to a temporary file. Return path to the file."""
 
 def dump_to_file(*output: str) -> str:
     """Dump `output` to a temporary file. Return path to the file."""

-    import tempfile
-

     with tempfile.NamedTemporaryFile(
         mode="w", prefix="blk_", suffix=".log", delete=False, encoding="utf8"
     ) as f:
     with tempfile.NamedTemporaryFile(
         mode="w", prefix="blk_", suffix=".log", delete=False, encoding="utf8"
     ) as f:


@@ -3453,6 +3592,13 @@ def dump_to_file(*output: str) -> str:
     return f.name
 
 
     return f.name
 
 

+@contextmanager
+def nullcontext() -> Iterator[None]:
+    """Return context manager that does nothing.
+    Similar to `nullcontext` from python 3.7"""
+    yield
+
+

 def diff(a: str, b: str, a_name: str, b_name: str) -> str:
     """Return a unified diff string between strings `a` and `b`."""
     import difflib
 def diff(a: str, b: str, a_name: str, b_name: str) -> str:
     """Return a unified diff string between strings `a` and `b`."""
     import difflib


@@ -3471,7 +3617,7 @@ def cancel(tasks: Iterable[asyncio.Task]) -> None:
         task.cancel()
 
 
         task.cancel()
 
 

-def shutdown(loop: BaseEventLoop) -> None:
+def shutdown(loop: asyncio.AbstractEventLoop) -> None:

     """Cancel all pending tasks on `loop`, wait for them, and close the loop."""
     try:
         if sys.version_info[:2] >= (3, 7):
     """Cancel all pending tasks on `loop`, wait for them, and close the loop."""
     try:
         if sys.version_info[:2] >= (3, 7):


@@ -3540,7 +3686,6 @@ def enumerate_with_length(
         if "\n" in leaf.value:
             return  # Multiline strings, we can't continue.
 
         if "\n" in leaf.value:
             return  # Multiline strings, we can't continue.
 

-        comment: Optional[Leaf]

         for comment in line.comments_after(leaf):
             length += len(comment.value)
 
         for comment in line.comments_after(leaf):
             length += len(comment.value)