Fix feature detection for parenthesized context managers (#4104)

CHANGES.md

@@ -10,6 +10,7 @@
 
 - Fix bug where `# fmt: off` automatically dedents when used with the `--line-ranges`
   option, even when it is not within the specified line range. (#4084)
+- Fix feature detection for parenthesized context managers (#4104)
 
 ### Preview style
 

src/black/__init__.py

@@ -1351,7 +1351,7 @@ def get_features_used(  # noqa: C901
             if (
                 len(atom_children) == 3
                 and atom_children[0].type == token.LPAR
-                and atom_children[1].type == syms.testlist_gexp
+                and _contains_asexpr(atom_children[1])
                 and atom_children[2].type == token.RPAR
             ):
                 features.add(Feature.PARENTHESIZED_CONTEXT_MANAGERS)
@@ -1384,6 +1384,22 @@ def get_features_used(  # noqa: C901
     return features
 
 
+def _contains_asexpr(node: Union[Node, Leaf]) -> bool:
+    """Return True if `node` contains an as-pattern."""
+    if node.type == syms.asexpr_test:
+        return True
+    elif node.type == syms.atom:
+        if (
+            len(node.children) == 3
+            and node.children[0].type == token.LPAR
+            and node.children[2].type == token.RPAR
+        ):
+            return _contains_asexpr(node.children[1])
+    elif node.type == syms.testlist_gexp:
+        return any(_contains_asexpr(child) for child in node.children)
+    return False
+
+
 def detect_target_versions(
     node: Node, *, future_imports: Optional[Set[str]] = None
 ) -> Set[TargetVersion]:

tests/data/cases/pep_572_remove_parens.py

@@ -1,4 +1,4 @@
-# flags: --minimum-version=3.8 --no-preview-line-length-1
+# flags: --minimum-version=3.8
 if (foo := 0):
     pass
 

tests/test_black.py

@@ -25,6 +25,7 @@
     List,
     Optional,
     Sequence,
+    Set,
     Type,
     TypeVar,
     Union,
@@ -874,71 +875,88 @@ def test_get_features_used_decorator(self) -> None:
             )
 
     def test_get_features_used(self) -> None:
-        node = black.lib2to3_parse("def f(*, arg): ...\n")
-        self.assertEqual(black.get_features_used(node), set())
-        node = black.lib2to3_parse("def f(*, arg,): ...\n")
-        self.assertEqual(black.get_features_used(node), {Feature.TRAILING_COMMA_IN_DEF})
-        node = black.lib2to3_parse("f(*arg,)\n")
-        self.assertEqual(
-            black.get_features_used(node), {Feature.TRAILING_COMMA_IN_CALL}
+        self.check_features_used("def f(*, arg): ...\n", set())
+        self.check_features_used(
+            "def f(*, arg,): ...\n", {Feature.TRAILING_COMMA_IN_DEF}
         )
-        node = black.lib2to3_parse("def f(*, arg): f'string'\n")
-        self.assertEqual(black.get_features_used(node), {Feature.F_STRINGS})
-        node = black.lib2to3_parse("123_456\n")
-        self.assertEqual(black.get_features_used(node), {Feature.NUMERIC_UNDERSCORES})
-        node = black.lib2to3_parse("123456\n")
-        self.assertEqual(black.get_features_used(node), set())
+        self.check_features_used("f(*arg,)\n", {Feature.TRAILING_COMMA_IN_CALL})
+        self.check_features_used("def f(*, arg): f'string'\n", {Feature.F_STRINGS})
+        self.check_features_used("123_456\n", {Feature.NUMERIC_UNDERSCORES})
+        self.check_features_used("123456\n", set())
+
         source, expected = read_data("cases", "function")
-        node = black.lib2to3_parse(source)
         expected_features = {
             Feature.TRAILING_COMMA_IN_CALL,
             Feature.TRAILING_COMMA_IN_DEF,
             Feature.F_STRINGS,
         }
-        self.assertEqual(black.get_features_used(node), expected_features)
-        node = black.lib2to3_parse(expected)
-        self.assertEqual(black.get_features_used(node), expected_features)
+        self.check_features_used(source, expected_features)
+        self.check_features_used(expected, expected_features)
+
         source, expected = read_data("cases", "expression")
-        node = black.lib2to3_parse(source)
-        self.assertEqual(black.get_features_used(node), set())
-        node = black.lib2to3_parse(expected)
-        self.assertEqual(black.get_features_used(node), set())
-        node = black.lib2to3_parse("lambda a, /, b: ...")
-        self.assertEqual(black.get_features_used(node), {Feature.POS_ONLY_ARGUMENTS})
-        node = black.lib2to3_parse("def fn(a, /, b): ...")
-        self.assertEqual(black.get_features_used(node), {Feature.POS_ONLY_ARGUMENTS})
-        node = black.lib2to3_parse("def fn(): yield a, b")
-        self.assertEqual(black.get_features_used(node), set())
-        node = black.lib2to3_parse("def fn(): return a, b")
-        self.assertEqual(black.get_features_used(node), set())
-        node = black.lib2to3_parse("def fn(): yield *b, c")
-        self.assertEqual(black.get_features_used(node), {Feature.UNPACKING_ON_FLOW})
-        node = black.lib2to3_parse("def fn(): return a, *b, c")
-        self.assertEqual(black.get_features_used(node), {Feature.UNPACKING_ON_FLOW})
-        node = black.lib2to3_parse("x = a, *b, c")
-        self.assertEqual(black.get_features_used(node), set())
-        node = black.lib2to3_parse("x: Any = regular")
-        self.assertEqual(black.get_features_used(node), set())
-        node = black.lib2to3_parse("x: Any = (regular, regular)")
-        self.assertEqual(black.get_features_used(node), set())
-        node = black.lib2to3_parse("x: Any = Complex(Type(1))[something]")
-        self.assertEqual(black.get_features_used(node), set())
-        node = black.lib2to3_parse("x: Tuple[int, ...] = a, b, c")
-        self.assertEqual(
-            black.get_features_used(node), {Feature.ANN_ASSIGN_EXTENDED_RHS}
+        self.check_features_used(source, set())
+        self.check_features_used(expected, set())
+
+        self.check_features_used("lambda a, /, b: ...\n", {Feature.POS_ONLY_ARGUMENTS})
+        self.check_features_used("def fn(a, /, b): ...", {Feature.POS_ONLY_ARGUMENTS})
+
+        self.check_features_used("def fn(): yield a, b", set())
+        self.check_features_used("def fn(): return a, b", set())
+        self.check_features_used("def fn(): yield *b, c", {Feature.UNPACKING_ON_FLOW})
+        self.check_features_used(
+            "def fn(): return a, *b, c", {Feature.UNPACKING_ON_FLOW}
         )
-        node = black.lib2to3_parse("try: pass\nexcept Something: pass")
-        self.assertEqual(black.get_features_used(node), set())
-        node = black.lib2to3_parse("try: pass\nexcept (*Something,): pass")
-        self.assertEqual(black.get_features_used(node), set())
-        node = black.lib2to3_parse("try: pass\nexcept *Group: pass")
-        self.assertEqual(black.get_features_used(node), {Feature.EXCEPT_STAR})
-        node = black.lib2to3_parse("a[*b]")
-        self.assertEqual(black.get_features_used(node), {Feature.VARIADIC_GENERICS})
-        node = black.lib2to3_parse("a[x, *y(), z] = t")
-        self.assertEqual(black.get_features_used(node), {Feature.VARIADIC_GENERICS})
-        node = black.lib2to3_parse("def fn(*args: *T): pass")
-        self.assertEqual(black.get_features_used(node), {Feature.VARIADIC_GENERICS})
+        self.check_features_used("x = a, *b, c", set())
+
+        self.check_features_used("x: Any = regular", set())
+        self.check_features_used("x: Any = (regular, regular)", set())
+        self.check_features_used("x: Any = Complex(Type(1))[something]", set())
+        self.check_features_used(
+            "x: Tuple[int, ...] = a, b, c", {Feature.ANN_ASSIGN_EXTENDED_RHS}
+        )
+
+        self.check_features_used("try: pass\nexcept Something: pass", set())
+        self.check_features_used("try: pass\nexcept (*Something,): pass", set())
+        self.check_features_used(
+            "try: pass\nexcept *Group: pass", {Feature.EXCEPT_STAR}
+        )
+
+        self.check_features_used("a[*b]", {Feature.VARIADIC_GENERICS})
+        self.check_features_used("a[x, *y(), z] = t", {Feature.VARIADIC_GENERICS})
+        self.check_features_used("def fn(*args: *T): pass", {Feature.VARIADIC_GENERICS})
+
+        self.check_features_used("with a: pass", set())
+        self.check_features_used("with a, b: pass", set())
+        self.check_features_used("with a as b: pass", set())
+        self.check_features_used("with a as b, c as d: pass", set())
+        self.check_features_used("with (a): pass", set())
+        self.check_features_used("with (a, b): pass", set())
+        self.check_features_used("with (a, b) as (c, d): pass", set())
+        self.check_features_used(
+            "with (a as b): pass", {Feature.PARENTHESIZED_CONTEXT_MANAGERS}
+        )
+        self.check_features_used(
+            "with ((a as b)): pass", {Feature.PARENTHESIZED_CONTEXT_MANAGERS}
+        )
+        self.check_features_used(
+            "with (a, b as c): pass", {Feature.PARENTHESIZED_CONTEXT_MANAGERS}
+        )
+        self.check_features_used(
+            "with (a, (b as c)): pass", {Feature.PARENTHESIZED_CONTEXT_MANAGERS}
+        )
+        self.check_features_used(
+            "with ((a, ((b as c)))): pass", {Feature.PARENTHESIZED_CONTEXT_MANAGERS}
+        )
+
+    def check_features_used(self, source: str, expected: Set[Feature]) -> None:
+        node = black.lib2to3_parse(source)
+        actual = black.get_features_used(node)
+        msg = f"Expected {expected} but got {actual} for {source!r}"
+        try:
+            self.assertEqual(actual, expected, msg=msg)
+        except AssertionError:
+            DebugVisitor.show(node)
+            raise
 
     def test_get_features_used_for_future_flags(self) -> None:
         for src, features in [