Deprecate Python 2 formatting support

docs/faq.md

@@ -74,13 +74,17 @@ disabled-by-default counterpart W504. E203 should be disabled while changes are
 
 ## Does Black support Python 2?
 
+```{warning}
+Python 2 support has been deprecated since 21.10b0.
+
+this support will be dropped in the first stable release, expected for January 2022.
+See [The Black Code Style](the_black_code_style/index.rst) for details.
+```
+
 For formatting, yes! [Install](getting_started.md#installation) with the `python2` extra
 to format Python 2 files too! In terms of running _Black_ though, Python 3.6 or newer is
 required.
 
-Note that this support will be dropped in the first stable release, expected for
-January 2022. See [The Black Code Style](the_black_code_style/index.rst) for details.
-
 ## Why does my linter or typechecker complain after I format my code?
 
 Some linters and other tools use magical comments (e.g., `# noqa`, `# type: ignore`) to

src/black/__init__.py

@@ -1058,6 +1058,15 @@ def f(
         versions = mode.target_versions
     else:
         versions = detect_target_versions(src_node)
+
+    # TODO: fully drop support and this code hopefully in January 2022 :D
+    if TargetVersion.PY27 in mode.target_versions or versions == {TargetVersion.PY27}:
+        msg = (
+            "DEPRECATION: Python 2 support will be removed in the first stable release"
+            "expected in January 2022."
+        )
+        err(msg, fg="yellow", bold=True)
+
     normalize_fmt_off(src_node)
     lines = LineGenerator(
         mode=mode,
@@ -1100,7 +1109,7 @@ def decode_bytes(src: bytes) -> Tuple[FileContent, Encoding, NewLine]:
         return tiow.read(), encoding, newline
 
 
-def get_features_used(node: Node) -> Set[Feature]:
+def get_features_used(node: Node) -> Set[Feature]:  # noqa: C901
     """Return a set of (relatively) new Python features used in this file.
 
     Currently looking for:
@@ -1110,6 +1119,7 @@ def get_features_used(node: Node) -> Set[Feature]:
     - positional only arguments in function signatures and lambdas;
     - assignment expression;
     - relaxed decorator syntax;
+    - print / exec statements;
     """
     features: Set[Feature] = set()
     for n in node.pre_order():
@@ -1158,6 +1168,11 @@ def get_features_used(node: Node) -> Set[Feature]:
                         if argch.type in STARS:
                             features.add(feature)
 
+        elif n.type == token.PRINT_STMT:
+            features.add(Feature.PRINT_STMT)
+        elif n.type == token.EXEC_STMT:
+            features.add(Feature.EXEC_STMT)
+
     return features
 
 

src/black/mode.py

@@ -41,9 +41,17 @@ class Feature(Enum):
     RELAXED_DECORATORS = 10
     FORCE_OPTIONAL_PARENTHESES = 50
 
+    # temporary; for Python 2 deprecation
+    PRINT_STMT = 200
+    EXEC_STMT = 201
+
 
 VERSION_TO_FEATURES: Dict[TargetVersion, Set[Feature]] = {
-    TargetVersion.PY27: {Feature.ASYNC_IDENTIFIERS},
+    TargetVersion.PY27: {
+        Feature.ASYNC_IDENTIFIERS,
+        Feature.PRINT_STMT,
+        Feature.EXEC_STMT,
+    },
     TargetVersion.PY33: {Feature.UNICODE_LITERALS, Feature.ASYNC_IDENTIFIERS},
     TargetVersion.PY34: {Feature.UNICODE_LITERALS, Feature.ASYNC_IDENTIFIERS},
     TargetVersion.PY35: {

src/blib2to3/pgen2/token.py

@@ -74,6 +74,9 @@
 COLONEQUAL: Final = 59
 N_TOKENS: Final = 60
 NT_OFFSET: Final = 256
+# temporary for Python 2 deprecation
+PRINT_STMT: Final = 316
+EXEC_STMT: Final = 288
 # --end constants--
 
 tok_name: Final[Dict[int, str]] = {}

tests/test_black.py

@@ -2014,6 +2014,21 @@ def test_get_sources_with_stdin_filename_and_force_exclude(self) -> None:
         )
 
 
+@pytest.mark.parametrize("explicit", [True, False], ids=["explicit", "autodetection"])
+def test_python_2_deprecation_with_target_version(explicit: bool) -> None:
+    args = [
+        "--config",
+        str(THIS_DIR / "empty.toml"),
+        str(DATA_DIR / "python2.py"),
+        "--check",
+    ]
+    if explicit:
+        args.append("--target-version=py27")
+    with cache_dir():
+        result = BlackRunner().invoke(black.main, args)
+    assert "DEPRECATION: Python 2 support will be removed" in result.stderr
+
+
 with open(black.__file__, "r", encoding="utf-8") as _bf:
     black_source_lines = _bf.readlines()