Use parentheses with equality check in walrus/assignment statements

CHANGES.md

@@ -14,6 +14,8 @@
 
 <!-- Changes that affect Black's preview style -->
 
+- Use parentheses with equality check in walrus/assigment statements (#2770)
+
 ### _Blackd_
 
 <!-- Changes to blackd -->

src/black/__init__.py

@@ -1095,7 +1095,7 @@ def format_ipynb_string(src_contents: str, *, fast: bool, mode: Mode) -> FileCon
     Operate cell-by-cell, only on code cells, only for Python notebooks.
     If the ``.ipynb`` originally had a trailing newline, it'll be preserved.
     """
-    trailing_newline = src_contents[-1] == "\n"
+    trailing_newline = (src_contents[-1] == "\n")
     modified = False
     nb = json.loads(src_contents)
     validate_metadata(nb)

src/black/linegen.py

@@ -98,6 +98,29 @@ def visit_default(self, node: LN) -> Iterator[Line]:
                 self.current_line.append(node)
         yield from super().visit_default(node)
 
+    def visit_comparison(self, node: Node) -> Iterator[Line]:
+        parent: Optional[Node] = node.parent
+        grandparent: Optional[Node] = parent.parent if parent else None
+        if (
+            # It is a preview style feature only
+            Preview.parentheses_in_equality_check_assignments in self.mode
+            and parent is not None
+            and Leaf(token.EQEQUAL, "==") in node.children
+            and (
+                parent.type == syms.namedexpr_test
+                or (
+                    grandparent is not None
+                    and grandparent.type in (syms.expr_stmt, syms.annassign)
+                )
+            )
+        ):
+            lpar = Leaf(token.LPAR, "(")
+            rpar = Leaf(token.RPAR, ")")
+            node.insert_child(0, lpar)
+            node.insert_child(len(node.children), rpar)
+
+        yield from self.visit_default(node)
+
     def visit_INDENT(self, node: Leaf) -> Iterator[Line]:
         """Increase indentation level, maybe yield a line."""
         # In blib2to3 INDENT never holds comments.

src/black/mode.py

@@ -128,6 +128,7 @@ class Preview(Enum):
 
     string_processing = auto()
     hug_simple_powers = auto()
+    parentheses_in_equality_check_assignments = auto()
 
 
 class Deprecated(UserWarning):

src/black/parsing.py

@@ -24,7 +24,7 @@
 
 ast3: Any
 
-_IS_PYPY = platform.python_implementation() == "PyPy"
+_IS_PYPY = (platform.python_implementation() == "PyPy")
 
 try:
     from typed_ast import ast3

src/black/trans.py

@@ -1479,7 +1479,7 @@ def passes_all_checks(i: Index) -> bool:
                 True iff ALL of the conditions listed in the 'Transformations'
                 section of this classes' docstring would be be met by returning @i.
             """
-            is_space = string[i] == " "
+            is_space = (string[i] == " ")
 
             is_not_escaped = True
             j = i - 1

src/black_primer/lib.py

@@ -29,7 +29,7 @@
 
 
 TEN_MINUTES_SECONDS = 600
-WINDOWS = system() == "Windows"
+WINDOWS = (system() == "Windows")
 BLACK_BINARY = "black.exe" if WINDOWS else "black"
 GIT_BINARY = "git.exe" if WINDOWS else "git"
 LOG = logging.getLogger(__name__)
@@ -158,7 +158,7 @@ async def black_run(
         )
         return
 
-    stdin_test = project_name.upper() == "STDIN"
+    stdin_test = (project_name.upper() == "STDIN")
     cmd = [str(which(BLACK_BINARY))]
     if "cli_arguments" in project_config and project_config["cli_arguments"]:
         cmd.extend(_flatten_cli_args(project_config["cli_arguments"]))
@@ -348,7 +348,7 @@ async def project_runner(
             continue
 
         repo_path: Optional[Path] = Path(__file__)
-        stdin_project = project_name.upper() == "STDIN"
+        stdin_project = (project_name.upper() == "STDIN")
         if not stdin_project:
             repo_path = await git_checkout_or_rebase(work_path, project_config, rebase)
             if not repo_path:

src/blackd/middlewares.py

@@ -10,7 +10,7 @@
 def cors(allow_headers: Iterable[str]) -> Middleware:
     @middleware
     async def impl(request: Request, handler: Handler) -> StreamResponse:
-        is_options = request.method == "OPTIONS"
+        is_options = (request.method == "OPTIONS")
         is_preflight = is_options and "Access-Control-Request-Method" in request.headers
         if is_preflight:
             resp = StreamResponse()

tests/data/paren_eq_check_in_assigments.py

@@ -0,0 +1,63 @@
+match_count += new_value == old_value
+
+on_windows: bool = (os.name == "nt")
+
+implementation_version = (
+    platform.python_version() if platform.python_implementation() == "CPython" else "Unknown"
+)
+
+is_mac = platform.system() == 'Darwin'
+
+s = y == 2 + y == 4
+
+name1 = name2 = name3
+
+name1 == name2 == name3
+
+check_sockets(on_windows=os.name == "nt")
+
+a = b in c and b == d
+
+a = b == c == d
+
+a = b == c in d
+
+a = b >= c == True
+
+a = b in c
+
+a = b > c
+
+# output
+
+match_count += (new_value == old_value)
+
+on_windows: bool = (os.name == "nt")
+
+implementation_version = (
+    platform.python_version()
+    if platform.python_implementation() == "CPython"
+    else "Unknown"
+)
+
+is_mac = (platform.system() == "Darwin")
+
+s = (y == 2 + y == 4)
+
+name1 = name2 = name3
+
+name1 == name2 == name3
+
+check_sockets(on_windows=os.name == "nt")
+
+a = b in c and b == d
+
+a = (b == c == d)
+
+a = (b == c in d)
+
+a = (b >= c == True)
+
+a = b in c
+
+a = b > c

tests/test_black.py

@@ -162,6 +162,7 @@ def test_piping(self) -> None:
             black.main,
             [
                 "-",
+                "--preview",
                 "--fast",
                 f"--line-length={black.DEFAULT_LINE_LENGTH}",
                 f"--config={EMPTY_CONFIG}",

tests/test_format.py

@@ -7,6 +7,7 @@
 import black
 from tests.util import (
     DEFAULT_MODE,
+    PREVIEW_MODE,
     PY36_VERSIONS,
     THIS_DIR,
     assert_format,
@@ -79,6 +80,7 @@
     "long_strings__edge_case",
     "long_strings__regression",
     "percent_precedence",
+    "paren_eq_check_in_assigments",
 ]
 
 SOURCES: List[str] = [
@@ -144,13 +146,13 @@ def test_simple_format(filename: str) -> None:
 
 @pytest.mark.parametrize("filename", PREVIEW_CASES)
 def test_preview_format(filename: str) -> None:
-    check_file(filename, black.Mode(preview=True))
+    check_file(filename, PREVIEW_MODE)
 
 
 @pytest.mark.parametrize("filename", SOURCES)
 def test_source_is_formatted(filename: str) -> None:
     path = THIS_DIR.parent / filename
-    check_file(str(path), DEFAULT_MODE, data=False)
+    check_file(str(path), PREVIEW_MODE, data=False)
 
 
 # =============== #

tests/util.py

@@ -25,6 +25,7 @@
 }
 
 DEFAULT_MODE = black.Mode()
+PREVIEW_MODE = black.Mode(preview=True)
 ff = partial(black.format_file_in_place, mode=DEFAULT_MODE, fast=True)
 fs = partial(black.format_str, mode=DEFAULT_MODE)