[GitHub] [airflow] uranusjr commented on a diff in pull request #28007: Add pre-commit hook to check session default value

[GitBox <gi...@apache.org>]

uranusjr commented on code in PR #28007:
URL: https://github.com/apache/airflow/pull/28007#discussion_r1049312171


##########
scripts/ci/pre_commit/pre_commit_new_session_in_provide_session.py:
##########
@@ -0,0 +1,123 @@
+#!/usr/bin/env python
+#
+# Licensed to the Apache Software Foundation (ASF) under one
+# or more contributor license agreements.  See the NOTICE file
+# distributed with this work for additional information
+# regarding copyright ownership.  The ASF licenses this file
+# to you under the Apache License, Version 2.0 (the
+# "License"); you may not use this file except in compliance
+# with the License.  You may obtain a copy of the License at
+#
+#   http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing,
+# software distributed under the License is distributed on an
+# "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+# KIND, either express or implied.  See the License for the
+# specific language governing permissions and limitations
+# under the License.
+from __future__ import annotations
+
+import ast
+import enum
+import itertools
+import pathlib
+import sys
+import typing
+
+
+class _SessionArgument(typing.NamedTuple):
+    argument: ast.arg
+    default: ast.expr | None
+
+
+def _get_session_arg_and_default(args: ast.arguments) -> _SessionArgument | None:
+    arguments = reversed([*args.args, *args.kwonlyargs])
+    defaults = reversed([*args.defaults, *args.kw_defaults])
+    for argument, default in itertools.zip_longest(arguments, defaults, fillvalue=None):
+        if argument is None:
+            continue  # Impossible since a function can't have more defaults than arguments.
+        if argument.arg != "session":
+            continue
+        return _SessionArgument(argument, default)
+    return None
+
+
+class _SessionDefault(enum.Enum):
+    none = "none"
+    new_session = "new_session"
+
+
+def _is_new_session_or_none(value: ast.expr) -> _SessionDefault | None:
+    """Whether an expression is NEW_SESSION.
+
+    Old code written before the introduction of NEW_SESSION (and even some new
+    if the contributor wasn't made aware of the addition) generally uses None
+    as the default value, so we add that to the check as well.
+    """
+    if isinstance(value, ast.Constant) and value.value is None:
+        return _SessionDefault.none
+    if isinstance(value, ast.Name) and value.id == "NEW_SESSION":
+        return _SessionDefault.new_session
+    # It's possible to do FOO = NEW_SESSION and reference FOO to work around
+    # this check, but let's rely on reviewers to catch this kind of shenanigans.
+    return None
+
+
+_ALLOWED_DECORATOR_NAMES = ("overload", "provide_session", "abstractmethod")
+
+
+def _is_decorated_correctly(nodes: list[ast.expr]) -> bool:
+    """Whether expected decorators are provided.
+
+    Three decorators would allow NEW_SESSION usages:
+
+    * ``@provide_session``: The canonical case.
+    * ``@overload``: A typing overload and not something to actually execute.
+    * ``@abstractmethod``: This will be overridden in a subclass anyway.
+    """
+    # This only accepts those decorators literally. Should be enough?
+    return any(isinstance(node, ast.Name) and node.id in _ALLOWED_DECORATOR_NAMES for node in nodes)
+
+
+def _annotation_has_none(value: ast.expr | None) -> bool:
+    if value is None:
+        return False
+    if isinstance(value, ast.Constant) and value.value is None:
+        return True
+    if isinstance(value, ast.BinOp) and isinstance(value.op, ast.BitOr):  # Type union.
+        return _annotation_has_none(value.left) or _annotation_has_none(value.right)
+    return False
+
+
+def _iter_incorrect_new_session_usages(path: pathlib.Path) -> typing.Iterator[ast.FunctionDef]:
+    """Check NEW_SESSION usages outside functions decorated with provide_session."""
+    for node in ast.walk(ast.parse(path.read_text("utf-8"), str(path))):
+        if not isinstance(node, ast.FunctionDef):
+            continue
+        session = _get_session_arg_and_default(node.args)
+        if session is None or session.default is None:
+            continue  # No session argument or the argument has no default, we're good.
+        if _is_decorated_correctly(node.decorator_list):
+            continue  # Has @provide_session so the default is expected.
+        default_kind = _is_new_session_or_none(session.default)
+        if default_kind is None:
+            continue  # Default value is not NEW_SESSION or None.
+        if default_kind == _SessionDefault.none and _annotation_has_none(session.argument.annotation):
+            continue  # None is OK if the argument is explicitly typed as None.
+        yield node
+
+
+def main(argv: list[str]) -> int:
+    paths = (pathlib.Path(filename) for filename in argv[1:])
+    errors = [(path, error) for path in paths for error in _iter_incorrect_new_session_usages(path)]
+    if errors:
+        print("Incorrect NEW_SESSION usages:", end="\n\n")

Review Comment:
   Actually we already do have a section on this! I’ll just link it here.
   
   https://github.com/apache/airflow/blob/main/CONTRIBUTING.rst#database-session-handling



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