Added not formatting files in gitignore (psf#1682) (#1734)

[etc/vim.git] / src / black / __init__.py

diff --git a/src/black/__init__.py b/src/black/__init__.py
index 0b734adca565e507aa3ed1daeec4cf49b1fcb61f..2bb42a470eadb617b3cb57c4ee4b9c0c76377d40 100644 (file)
--- a/src/black/__init__.py
+++ b/src/black/__init__.py
@@ -48,7 +48,20 @@ from appdirs import user_cache_dir
 from dataclasses import dataclass, field, replace
 import click
 import toml
 from dataclasses import dataclass, field, replace
 import click
 import toml

-from typed_ast import ast3, ast27
+
+try:
+    from typed_ast import ast3, ast27
+except ImportError:
+    if sys.version_info < (3, 8):
+        print(
+            "The typed_ast package is not installed.\n"
+            "You can install it with `python3 -m pip install typed-ast`.",
+            file=sys.stderr,
+        )
+        sys.exit(1)
+    else:
+        ast3 = ast27 = ast
+

 from pathspec import PathSpec
 
 # lib2to3 fork
 from pathspec import PathSpec
 
 # lib2to3 fork


@@ -69,7 +82,7 @@ if TYPE_CHECKING:
     import colorama  # noqa: F401
 
 DEFAULT_LINE_LENGTH = 88
     import colorama  # noqa: F401
 
 DEFAULT_LINE_LENGTH = 88

-DEFAULT_EXCLUDES = r"/(\.direnv|\.eggs|\.git|\.hg|\.mypy_cache|\.nox|\.tox|\.venv|\.svn|_build|buck-out|build|dist)/"  # noqa: B950
+DEFAULT_EXCLUDES = r"/(\.direnv|\.eggs|\.git|\.hg|\.mypy_cache|\.nox|\.tox|\.venv|venv|\.svn|_build|buck-out|build|dist)/"  # noqa: B950

 DEFAULT_INCLUDES = r"\.pyi?$"
 CACHE_DIR = Path(user_cache_dir("black", version=__version__))
 STDIN_PLACEHOLDER = "__BLACK_STDIN_FILENAME__"
 DEFAULT_INCLUDES = r"\.pyi?$"
 CACHE_DIR = Path(user_cache_dir("black", version=__version__))
 STDIN_PLACEHOLDER = "__BLACK_STDIN_FILENAME__"


@@ -289,11 +302,15 @@ def supports_feature(target_versions: Set[TargetVersion], feature: Feature) -> b
     return all(feature in VERSION_TO_FEATURES[version] for version in target_versions)
 
 
     return all(feature in VERSION_TO_FEATURES[version] for version in target_versions)
 
 

-def find_pyproject_toml(path_search_start: Iterable[str]) -> Optional[str]:
+def find_pyproject_toml(path_search_start: Tuple[str, ...]) -> Optional[str]:

     """Find the absolute filepath to a pyproject.toml if it exists"""
     path_project_root = find_project_root(path_search_start)
     path_pyproject_toml = path_project_root / "pyproject.toml"
     """Find the absolute filepath to a pyproject.toml if it exists"""
     path_project_root = find_project_root(path_search_start)
     path_pyproject_toml = path_project_root / "pyproject.toml"

-    return str(path_pyproject_toml) if path_pyproject_toml.is_file() else None
+    if path_pyproject_toml.is_file():
+        return str(path_pyproject_toml)
+
+    path_user_pyproject_toml = find_user_pyproject_toml()
+    return str(path_user_pyproject_toml) if path_user_pyproject_toml.is_file() else None

 
 
 def parse_pyproject_toml(path_config: str) -> Dict[str, Any]:
 
 
 def parse_pyproject_toml(path_config: str) -> Dict[str, Any]:


@@ -363,6 +380,17 @@ def target_version_option_callback(
     return [TargetVersion[val.upper()] for val in v]
 
 
     return [TargetVersion[val.upper()] for val in v]
 
 

+def validate_regex(
+    ctx: click.Context,
+    param: click.Parameter,
+    value: Optional[str],
+) -> Optional[Pattern]:
+    try:
+        return re_compile_maybe_verbose(value) if value is not None else None
+    except re.error:
+        raise click.BadParameter("Not a valid regular expression")
+
+

 @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(
 @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(


@@ -417,8 +445,8 @@ def target_version_option_callback(
     "--check",
     is_flag=True,
     help=(
     "--check",
     is_flag=True,
     help=(

-        "Don't write the files back, just return the status.  Return code 0 means"
-        " nothing would change.  Return code 1 means some files would be reformatted."
+        "Don't write the files back, just return the status. Return code 0 means"
+        " nothing would change. Return code 1 means some files would be reformatted."

         " Return code 123 means there was an internal error."
     ),
 )
         " Return code 123 means there was an internal error."
     ),
 )


@@ -441,11 +469,12 @@ def target_version_option_callback(
     "--include",
     type=str,
     default=DEFAULT_INCLUDES,
     "--include",
     type=str,
     default=DEFAULT_INCLUDES,

+    callback=validate_regex,

     help=(
         "A regular expression that matches files and directories that should be"
     help=(
         "A regular expression that matches files and directories that should be"

-        " included on recursive searches.  An empty value means all files are included"
-        " regardless of the name.  Use forward slashes for directories on all platforms"
-        " (Windows, too).  Exclusions are calculated first, inclusions later."
+        " included on recursive searches. An empty value means all files are included"
+        " regardless of the name. Use forward slashes for directories on all platforms"
+        " (Windows, too). Exclusions are calculated first, inclusions later."

     ),
     show_default=True,
 )
     ),
     show_default=True,
 )


@@ -453,17 +482,28 @@ def target_version_option_callback(
     "--exclude",
     type=str,
     default=DEFAULT_EXCLUDES,
     "--exclude",
     type=str,
     default=DEFAULT_EXCLUDES,

+    callback=validate_regex,

     help=(
         "A regular expression that matches files and directories that should be"
     help=(
         "A regular expression that matches files and directories that should be"

-        " excluded on recursive searches.  An empty value means no paths are excluded."
-        " Use forward slashes for directories on all platforms (Windows, too). "
+        " excluded on recursive searches. An empty value means no paths are excluded."
+        " Use forward slashes for directories on all platforms (Windows, too)."

         " Exclusions are calculated first, inclusions later."
     ),
     show_default=True,
 )
         " Exclusions are calculated first, inclusions later."
     ),
     show_default=True,
 )

+@click.option(
+    "--extend-exclude",
+    type=str,
+    callback=validate_regex,
+    help=(
+        "Like --exclude, but adds additional files and directories on top of the"
+        " excluded ones. (Useful if you simply want to add to the default)"
+    ),
+)

 @click.option(
     "--force-exclude",
     type=str,
 @click.option(
     "--force-exclude",
     type=str,

+    callback=validate_regex,

     help=(
         "Like --exclude, but files and directories matching this regex will be "
         "excluded even when they are passed explicitly as arguments."
     help=(
         "Like --exclude, but files and directories matching this regex will be "
         "excluded even when they are passed explicitly as arguments."


@@ -493,7 +533,7 @@ def target_version_option_callback(
     is_flag=True,
     help=(
         "Also emit messages to stderr about files that were not changed or were ignored"
     is_flag=True,
     help=(
         "Also emit messages to stderr about files that were not changed or were ignored"

-        " due to --exclude=."
+        " due to exclusion patterns."

     ),
 )
 @click.version_option(version=__version__)
     ),
 )
 @click.version_option(version=__version__)


@@ -535,9 +575,10 @@ def main(
     experimental_string_processing: bool,
     quiet: bool,
     verbose: bool,
     experimental_string_processing: bool,
     quiet: bool,
     verbose: bool,

-    include: str,
-    exclude: str,
-    force_exclude: Optional[str],
+    include: Pattern,
+    exclude: Pattern,
+    extend_exclude: Optional[Pattern],
+    force_exclude: Optional[Pattern],

     stdin_filename: Optional[str],
     src: Tuple[str, ...],
     config: Optional[str],
     stdin_filename: Optional[str],
     src: Tuple[str, ...],
     config: Optional[str],


@@ -570,6 +611,7 @@ def main(
         verbose=verbose,
         include=include,
         exclude=exclude,
         verbose=verbose,
         include=include,
         exclude=exclude,

+        extend_exclude=extend_exclude,

         force_exclude=force_exclude,
         report=report,
         stdin_filename=stdin_filename,
         force_exclude=force_exclude,
         report=report,
         stdin_filename=stdin_filename,


@@ -608,30 +650,14 @@ def get_sources(
     src: Tuple[str, ...],
     quiet: bool,
     verbose: bool,
     src: Tuple[str, ...],
     quiet: bool,
     verbose: bool,

-    include: str,
-    exclude: str,
-    force_exclude: Optional[str],
+    include: Pattern[str],
+    exclude: Pattern[str],
+    extend_exclude: Optional[Pattern[str]],
+    force_exclude: Optional[Pattern[str]],

     report: "Report",
     stdin_filename: Optional[str],
 ) -> Set[Path]:
     """Compute the set of files to be formatted."""
     report: "Report",
     stdin_filename: Optional[str],
 ) -> Set[Path]:
     """Compute the set of files to be formatted."""

-    try:
-        include_regex = re_compile_maybe_verbose(include)
-    except re.error:
-        err(f"Invalid regular expression for include given: {include!r}")
-        ctx.exit(2)
-    try:
-        exclude_regex = re_compile_maybe_verbose(exclude)
-    except re.error:
-        err(f"Invalid regular expression for exclude given: {exclude!r}")
-        ctx.exit(2)
-    try:
-        force_exclude_regex = (
-            re_compile_maybe_verbose(force_exclude) if force_exclude else None
-        )
-    except re.error:
-        err(f"Invalid regular expression for force_exclude given: {force_exclude!r}")
-        ctx.exit(2)

 
     root = find_project_root(src)
     sources: Set[Path] = set()
 
     root = find_project_root(src)
     sources: Set[Path] = set()


@@ -653,8 +679,8 @@ def get_sources(
 
             normalized_path = "/" + normalized_path
             # Hard-exclude any files that matches the `--force-exclude` regex.
 
             normalized_path = "/" + normalized_path
             # Hard-exclude any files that matches the `--force-exclude` regex.

-            if force_exclude_regex:
-                force_exclude_match = force_exclude_regex.search(normalized_path)
+            if force_exclude:
+                force_exclude_match = force_exclude.search(normalized_path)

             else:
                 force_exclude_match = None
             if force_exclude_match and force_exclude_match.group(0):
             else:
                 force_exclude_match = None
             if force_exclude_match and force_exclude_match.group(0):


@@ -670,9 +696,10 @@ def get_sources(
                 gen_python_files(
                     p.iterdir(),
                     root,
                 gen_python_files(
                     p.iterdir(),
                     root,

-                    include_regex,
-                    exclude_regex,
-                    force_exclude_regex,
+                    include,
+                    exclude,
+                    extend_exclude,
+                    force_exclude,

                     report,
                     gitignore,
                 )
                     report,
                     gitignore,
                 )


@@ -820,7 +847,7 @@ async def schedule_formatting(
         ): src
         for src in sorted(sources)
     }
         ): src
         for src in sorted(sources)
     }

-    pending: Iterable["asyncio.Future[bool]"] = tasks.keys()
+    pending = tasks.keys()

     try:
         loop.add_signal_handler(signal.SIGINT, cancel, pending)
         loop.add_signal_handler(signal.SIGTERM, cancel, pending)
     try:
         loop.add_signal_handler(signal.SIGINT, cancel, pending)
         loop.add_signal_handler(signal.SIGTERM, cancel, pending)


@@ -883,7 +910,7 @@ def format_file_in_place(
         dst_name = f"{src}\t{now} +0000"
         diff_contents = diff(src_contents, dst_contents, src_name, dst_name)
 
         dst_name = f"{src}\t{now} +0000"
         diff_contents = diff(src_contents, dst_contents, src_name, dst_name)
 

-        if write_back == write_back.COLOR_DIFF:
+        if write_back == WriteBack.COLOR_DIFF:

             diff_contents = color_diff(diff_contents)
 
         with lock or nullcontext():
             diff_contents = color_diff(diff_contents)
 
         with lock or nullcontext():


@@ -1480,7 +1507,7 @@ class Line:
     comments: Dict[LeafID, List[Leaf]] = field(default_factory=dict)
     bracket_tracker: BracketTracker = field(default_factory=BracketTracker)
     inside_brackets: bool = False
     comments: Dict[LeafID, List[Leaf]] = field(default_factory=dict)
     bracket_tracker: BracketTracker = field(default_factory=BracketTracker)
     inside_brackets: bool = False

-    should_split: bool = False
+    should_split_rhs: bool = False

     magic_trailing_comma: Optional[Leaf] = None
 
     def append(self, leaf: Leaf, preformatted: bool = False) -> None:
     magic_trailing_comma: Optional[Leaf] = None
 
     def append(self, leaf: Leaf, preformatted: bool = False) -> None:


@@ -1792,7 +1819,7 @@ class Line:
             mode=self.mode,
             depth=self.depth,
             inside_brackets=self.inside_brackets,
             mode=self.mode,
             depth=self.depth,
             inside_brackets=self.inside_brackets,

-            should_split=self.should_split,
+            should_split_rhs=self.should_split_rhs,

             magic_trailing_comma=self.magic_trailing_comma,
         )
 
             magic_trailing_comma=self.magic_trailing_comma,
         )
 


@@ -2049,6 +2076,8 @@ class LineGenerator(Visitor[Line]):
 
     def visit_simple_stmt(self, node: Node) -> Iterator[Line]:
         """Visit a statement without nested statements."""
 
     def visit_simple_stmt(self, node: Node) -> Iterator[Line]:
         """Visit a statement without nested statements."""

+        if first_child_is_arith(node):
+            wrap_in_parentheses(node, node.children[0], visible=False)

         is_suite_like = node.parent and node.parent.type in STATEMENT
         if is_suite_like:
             if self.mode.is_pyi and is_stub_body(node):
         is_suite_like = node.parent and node.parent.type in STATEMENT
         if is_suite_like:
             if self.mode.is_pyi and is_stub_body(node):


@@ -2712,7 +2741,7 @@ def transform_line(
     transformers: List[Transformer]
     if (
         not line.contains_uncollapsable_type_comments()
     transformers: List[Transformer]
     if (
         not line.contains_uncollapsable_type_comments()

-        and not line.should_split
+        and not line.should_split_rhs

         and not line.magic_trailing_comma
         and (
             is_line_short_enough(line, line_length=mode.line_length, line_str=line_str)
         and not line.magic_trailing_comma
         and (
             is_line_short_enough(line, line_length=mode.line_length, line_str=line_str)


@@ -4387,7 +4416,7 @@ class StringParenWrapper(CustomSplitMapMixin, BaseStringSplitter):
             mode=line.mode,
             depth=line.depth + 1,
             inside_brackets=True,
             mode=line.mode,
             depth=line.depth + 1,
             inside_brackets=True,

-            should_split=line.should_split,
+            should_split_rhs=line.should_split_rhs,

             magic_trailing_comma=line.magic_trailing_comma,
         )
         string_leaf = Leaf(token.STRING, string_value)
             magic_trailing_comma=line.magic_trailing_comma,
         )
         string_leaf = Leaf(token.STRING, string_value)


@@ -5010,7 +5039,7 @@ def bracket_split_build_line(
         for comment_after in original.comments_after(leaf):
             result.append(comment_after, preformatted=True)
     if is_body and should_split_line(result, opening_bracket):
         for comment_after in original.comments_after(leaf):
             result.append(comment_after, preformatted=True)
     if is_body and should_split_line(result, opening_bracket):

-        result.should_split = True
+        result.should_split_rhs = True

     return result
 
 
     return result
 
 


@@ -5368,10 +5397,7 @@ def normalize_invisible_parens(node: Node, parens_after: Set[str]) -> None:
             check_lpar = True
 
         if check_lpar:
             check_lpar = True
 
         if check_lpar:

-            if is_walrus_assignment(child):
-                pass
-
-            elif child.type == syms.atom:
+            if child.type == syms.atom:

                 if maybe_make_parens_invisible_in_atom(child, parent=node):
                     wrap_in_parentheses(node, child, visible=False)
             elif is_one_tuple(child):
                 if maybe_make_parens_invisible_in_atom(child, parent=node):
                     wrap_in_parentheses(node, child, visible=False)
             elif is_one_tuple(child):


@@ -5543,6 +5569,7 @@ def maybe_make_parens_invisible_in_atom(node: LN, parent: LN) -> bool:
     Returns whether the node should itself be wrapped in invisible parentheses.
 
     """
     Returns whether the node should itself be wrapped in invisible parentheses.
 
     """

+

     if (
         node.type != syms.atom
         or is_empty_tuple(node)
     if (
         node.type != syms.atom
         or is_empty_tuple(node)


@@ -5552,6 +5579,10 @@ def maybe_make_parens_invisible_in_atom(node: LN, parent: LN) -> bool:
     ):
         return False
 
     ):
         return False
 

+    if is_walrus_assignment(node):
+        if parent.type in [syms.annassign, syms.expr_stmt]:
+            return False
+

     first = node.children[0]
     last = node.children[-1]
     if first.type == token.LPAR and last.type == token.RPAR:
     first = node.children[0]
     last = node.children[-1]
     if first.type == token.LPAR and last.type == token.RPAR:


@@ -5613,6 +5644,17 @@ def unwrap_singleton_parenthesis(node: LN) -> Optional[LN]:
     return wrapped
 
 
     return wrapped
 
 

+def first_child_is_arith(node: Node) -> bool:
+    """Whether first child is an arithmetic or a binary arithmetic expression"""
+    expr_types = {
+        syms.arith_expr,
+        syms.shift_expr,
+        syms.xor_expr,
+        syms.and_expr,
+    }
+    return bool(node.children and node.children[0].type in expr_types)
+
+

 def wrap_in_parentheses(parent: Node, child: LN, *, visible: bool = True) -> None:
     """Wrap `child` in parentheses.
 
 def wrap_in_parentheses(parent: Node, child: LN, *, visible: bool = True) -> None:
     """Wrap `child` in parentheses.
 


@@ -6097,17 +6139,27 @@ def normalize_path_maybe_ignore(
     return normalized_path
 
 
     return normalized_path
 
 

+def path_is_excluded(
+    normalized_path: str,
+    pattern: Optional[Pattern[str]],
+) -> bool:
+    match = pattern.search(normalized_path) if pattern else None
+    return bool(match and match.group(0))
+
+

 def gen_python_files(
     paths: Iterable[Path],
     root: Path,
     include: Optional[Pattern[str]],
     exclude: Pattern[str],
 def gen_python_files(
     paths: Iterable[Path],
     root: Path,
     include: Optional[Pattern[str]],
     exclude: Pattern[str],

+    extend_exclude: Optional[Pattern[str]],

     force_exclude: Optional[Pattern[str]],
     report: "Report",
     gitignore: PathSpec,
 ) -> Iterator[Path]:
     """Generate all files under `path` whose paths are not excluded by the
     force_exclude: Optional[Pattern[str]],
     report: "Report",
     gitignore: PathSpec,
 ) -> Iterator[Path]:
     """Generate all files under `path` whose paths are not excluded by the

-    `exclude_regex` or `force_exclude` regexes, but are included by the `include` regex.
+    `exclude_regex`, `extend_exclude`, or `force_exclude` regexes,
+    but are included by the `include` regex.

 
     Symbolic links pointing outside of the `root` directory are ignored.
 
 
     Symbolic links pointing outside of the `root` directory are ignored.
 


@@ -6124,20 +6176,22 @@ def gen_python_files(
             report.path_ignored(child, "matches the .gitignore file content")
             continue
 
             report.path_ignored(child, "matches the .gitignore file content")
             continue
 

-        # Then ignore with `--exclude` and `--force-exclude` options.
+        # Then ignore with `--exclude` `--extend-exclude` and `--force-exclude` options.

         normalized_path = "/" + normalized_path
         if child.is_dir():
             normalized_path += "/"
 
         normalized_path = "/" + normalized_path
         if child.is_dir():
             normalized_path += "/"
 

-        exclude_match = exclude.search(normalized_path) if exclude else None
-        if exclude_match and exclude_match.group(0):
+        if path_is_excluded(normalized_path, exclude):

             report.path_ignored(child, "matches the --exclude regular expression")
             continue
 
             report.path_ignored(child, "matches the --exclude regular expression")
             continue
 

-        force_exclude_match = (
-            force_exclude.search(normalized_path) if force_exclude else None
-        )
-        if force_exclude_match and force_exclude_match.group(0):
+        if path_is_excluded(normalized_path, extend_exclude):
+            report.path_ignored(
+                child, "matches the --extend-exclude regular expression"
+            )
+            continue
+
+        if path_is_excluded(normalized_path, force_exclude):

             report.path_ignored(child, "matches the --force-exclude regular expression")
             continue
 
             report.path_ignored(child, "matches the --force-exclude regular expression")
             continue
 


@@ -6147,6 +6201,7 @@ def gen_python_files(
                 root,
                 include,
                 exclude,
                 root,
                 include,
                 exclude,

+                extend_exclude,

                 force_exclude,
                 report,
                 gitignore,
                 force_exclude,
                 report,
                 gitignore,


@@ -6159,7 +6214,7 @@ def gen_python_files(
 
 
 @lru_cache()
 
 
 @lru_cache()

-def find_project_root(srcs: Iterable[str]) -> Path:
+def find_project_root(srcs: Tuple[str, ...]) -> Path:

     """Return a directory containing .git, .hg, or pyproject.toml.
 
     That directory will be a common parent of all files and directories
     """Return a directory containing .git, .hg, or pyproject.toml.
 
     That directory will be a common parent of all files and directories


@@ -6197,6 +6252,22 @@ def find_project_root(srcs: Iterable[str]) -> Path:
     return directory
 
 
     return directory
 
 

+@lru_cache()
+def find_user_pyproject_toml() -> Path:
+    r"""Return the path to the top-level user configuration for black.
+
+    This looks for ~\.black on Windows and ~/.config/black on Linux and other
+    Unix systems.
+    """
+    if sys.platform == "win32":
+        # Windows
+        user_config_path = Path.home() / ".black"
+    else:
+        config_root = os.environ.get("XDG_CONFIG_HOME", "~/.config")
+        user_config_path = Path(config_root).expanduser() / "black"
+    return user_config_path.resolve()
+
+

 @dataclass
 class Report:
     """Provides a reformatting counter. Can be rendered with `str(report)`."""
 @dataclass
 class Report:
     """Provides a reformatting counter. Can be rendered with `str(report)`."""


@@ -6298,7 +6369,12 @@ def parse_ast(src: str) -> Union[ast.AST, ast3.AST, ast27.AST]:
                 return ast3.parse(src, filename, feature_version=feature_version)
             except SyntaxError:
                 continue
                 return ast3.parse(src, filename, feature_version=feature_version)
             except SyntaxError:
                 continue

-
+    if ast27.__name__ == "ast":
+        raise SyntaxError(
+            "The requested source code has invalid Python 3 syntax.\n"
+            "If you are trying to format Python 2 files please reinstall Black"
+            " with the 'python2' extra: `python3 -m pip install black[python2]`."
+        )

     return ast27.parse(src)
 
 
     return ast27.parse(src)
 
 


@@ -6425,14 +6501,14 @@ def assert_stable(src: str, dst: str, mode: Mode) -> None:
 
 
 @mypyc_attr(patchable=True)
 
 
 @mypyc_attr(patchable=True)

-def dump_to_file(*output: str) -> str:
+def dump_to_file(*output: str, ensure_final_newline: bool = True) -> str:

     """Dump `output` to a temporary file. Return path to the file."""
     with tempfile.NamedTemporaryFile(
         mode="w", prefix="blk_", suffix=".log", delete=False, encoding="utf8"
     ) as f:
         for lines in output:
             f.write(lines)
     """Dump `output` to a temporary file. Return path to the file."""
     with tempfile.NamedTemporaryFile(
         mode="w", prefix="blk_", suffix=".log", delete=False, encoding="utf8"
     ) as f:
         for lines in output:
             f.write(lines)

-            if lines and lines[-1] != "\n":
+            if ensure_final_newline and lines and lines[-1] != "\n":

                 f.write("\n")
     return f.name
 
                 f.write("\n")
     return f.name
 


@@ -6450,11 +6526,20 @@ 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
 
     """Return a unified diff string between strings `a` and `b`."""
     import difflib
 

-    a_lines = [line + "\n" for line in a.splitlines()]
-    b_lines = [line + "\n" for line in b.splitlines()]
-    return "".join(
-        difflib.unified_diff(a_lines, b_lines, fromfile=a_name, tofile=b_name, n=5)
-    )
+    a_lines = [line for line in a.splitlines(keepends=True)]
+    b_lines = [line for line in b.splitlines(keepends=True)]
+    diff_lines = []
+    for line in difflib.unified_diff(
+        a_lines, b_lines, fromfile=a_name, tofile=b_name, n=5
+    ):
+        # Work around https://bugs.python.org/issue2142
+        # See https://www.gnu.org/software/diffutils/manual/html_node/Incomplete-Lines.html
+        if line[-1] == "\n":
+            diff_lines.append(line)
+        else:
+            diff_lines.append(line + "\n")
+            diff_lines.append("\\ No newline at end of file\n")
+    return "".join(diff_lines)

 
 
 def cancel(tasks: Iterable["asyncio.Task[Any]"]) -> None:
 
 
 def cancel(tasks: Iterable["asyncio.Task[Any]"]) -> None: