[3.9] bpo-44852: Support ignoring specific DeprecationWarnings wholesale in regrtest (GH-27634) (GH-27785)

(cherry picked from commit a0a6d39295a30434b088f4b66439bf5ea21a3e4e)

Co-authored-by: Łukasz Langa <lukasz@langa.pl>

4 files changed, 269 insertions, 0 deletions

diff --git a/Lib/test/support/__init__.py b/Lib/test/support/__init__.py
index ff7db991..39dea88 100644
--- a/Lib/test/support/__init__.py
+++ b/Lib/test/support/__init__.py
@@ -3241,3 +3241,31 @@ def infinite_recursion(max_depth=75):
         yield
     finally:
         sys.setrecursionlimit(original_depth)
+
+def ignore_deprecations_from(module: str, *, like: str) -> object:
+    token = object()
+    warnings.filterwarnings(
+        "ignore",
+        category=DeprecationWarning,
+        module=module,
+        message=like + fr"(?#support{id(token)})",
+    )
+    return token
+
+def clear_ignored_deprecations(*tokens: object) -> None:
+    if not tokens:
+        raise ValueError("Provide token or tokens returned by ignore_deprecations_from")
+
+    new_filters = []
+    for action, message, category, module, lineno in warnings.filters:
+        if action == "ignore" and category is DeprecationWarning:
+            if isinstance(message, re.Pattern):
+                message = message.pattern
+            if tokens:
+                endswith = tuple(rf"(?#support{id(token)})" for token in tokens)
+            if message.endswith(endswith):
+                continue
+        new_filters.append((action, message, category, module, lineno))
+    if warnings.filters != new_filters:
+        warnings.filters[:] = new_filters
+        warnings._filters_mutated()
diff --git a/Lib/test/support/warnings_helper.py b/Lib/test/support/warnings_helper.py
new file mode 100644
index 0000000..a024fbe
--- /dev/null
+++ b/Lib/test/support/warnings_helper.py
@@ -0,0 +1,199 @@
+import contextlib
+import functools
+import re
+import sys
+import warnings
+
+
+def check_syntax_warning(testcase, statement, errtext='',
+                         *, lineno=1, offset=None):
+    # Test also that a warning is emitted only once.
+    from test.support import check_syntax_error
+    with warnings.catch_warnings(record=True) as warns:
+        warnings.simplefilter('always', SyntaxWarning)
+        compile(statement, '<testcase>', 'exec')
+    testcase.assertEqual(len(warns), 1, warns)
+
+    warn, = warns
+    testcase.assertTrue(issubclass(warn.category, SyntaxWarning),
+                        warn.category)
+    if errtext:
+        testcase.assertRegex(str(warn.message), errtext)
+    testcase.assertEqual(warn.filename, '<testcase>')
+    testcase.assertIsNotNone(warn.lineno)
+    if lineno is not None:
+        testcase.assertEqual(warn.lineno, lineno)
+
+    # SyntaxWarning should be converted to SyntaxError when raised,
+    # since the latter contains more information and provides better
+    # error report.
+    with warnings.catch_warnings(record=True) as warns:
+        warnings.simplefilter('error', SyntaxWarning)
+        check_syntax_error(testcase, statement, errtext,
+                           lineno=lineno, offset=offset)
+    # No warnings are leaked when a SyntaxError is raised.
+    testcase.assertEqual(warns, [])
+
+
+def ignore_warnings(*, category):
+    """Decorator to suppress deprecation warnings.
+
+    Use of context managers to hide warnings make diffs
+    more noisy and tools like 'git blame' less useful.
+    """
+    def decorator(test):
+        @functools.wraps(test)
+        def wrapper(self, *args, **kwargs):
+            with warnings.catch_warnings():
+                warnings.simplefilter('ignore', category=category)
+                return test(self, *args, **kwargs)
+        return wrapper
+    return decorator
+
+
+class WarningsRecorder(object):
+    """Convenience wrapper for the warnings list returned on
+       entry to the warnings.catch_warnings() context manager.
+    """
+    def __init__(self, warnings_list):
+        self._warnings = warnings_list
+        self._last = 0
+
+    def __getattr__(self, attr):
+        if len(self._warnings) > self._last:
+            return getattr(self._warnings[-1], attr)
+        elif attr in warnings.WarningMessage._WARNING_DETAILS:
+            return None
+        raise AttributeError("%r has no attribute %r" % (self, attr))
+
+    @property
+    def warnings(self):
+        return self._warnings[self._last:]
+
+    def reset(self):
+        self._last = len(self._warnings)
+
+
+@contextlib.contextmanager
+def check_warnings(*filters, **kwargs):
+    """Context manager to silence warnings.
+
+    Accept 2-tuples as positional arguments:
+        ("message regexp", WarningCategory)
+
+    Optional argument:
+     - if 'quiet' is True, it does not fail if a filter catches nothing
+        (default True without argument,
+         default False if some filters are defined)
+
+    Without argument, it defaults to:
+        check_warnings(("", Warning), quiet=True)
+    """
+    quiet = kwargs.get('quiet')
+    if not filters:
+        filters = (("", Warning),)
+        # Preserve backward compatibility
+        if quiet is None:
+            quiet = True
+    return _filterwarnings(filters, quiet)
+
+
+@contextlib.contextmanager
+def check_no_warnings(testcase, message='', category=Warning, force_gc=False):
+    """Context manager to check that no warnings are emitted.
+
+    This context manager enables a given warning within its scope
+    and checks that no warnings are emitted even with that warning
+    enabled.
+
+    If force_gc is True, a garbage collection is attempted before checking
+    for warnings. This may help to catch warnings emitted when objects
+    are deleted, such as ResourceWarning.
+
+    Other keyword arguments are passed to warnings.filterwarnings().
+    """
+    from test.support import gc_collect
+    with warnings.catch_warnings(record=True) as warns:
+        warnings.filterwarnings('always',
+                                message=message,
+                                category=category)
+        yield
+        if force_gc:
+            gc_collect()
+    testcase.assertEqual(warns, [])
+
+
+@contextlib.contextmanager
+def check_no_resource_warning(testcase):
+    """Context manager to check that no ResourceWarning is emitted.
+
+    Usage:
+
+        with check_no_resource_warning(self):
+            f = open(...)
+            ...
+            del f
+
+    You must remove the object which may emit ResourceWarning before
+    the end of the context manager.
+    """
+    with check_no_warnings(testcase, category=ResourceWarning, force_gc=True):
+        yield
+
+
+def _filterwarnings(filters, quiet=False):
+    """Catch the warnings, then check if all the expected
+    warnings have been raised and re-raise unexpected warnings.
+    If 'quiet' is True, only re-raise the unexpected warnings.
+    """
+    # Clear the warning registry of the calling module
+    # in order to re-raise the warnings.
+    frame = sys._getframe(2)
+    registry = frame.f_globals.get('__warningregistry__')
+    if registry:
+        registry.clear()
+    with warnings.catch_warnings(record=True) as w:
+        # Set filter "always" to record all warnings.  Because
+        # test_warnings swap the module, we need to look up in
+        # the sys.modules dictionary.
+        sys.modules['warnings'].simplefilter("always")
+        yield WarningsRecorder(w)
+    # Filter the recorded warnings
+    reraise = list(w)
+    missing = []
+    for msg, cat in filters:
+        seen = False
+        for w in reraise[:]:
+            warning = w.message
+            # Filter out the matching messages
+            if (re.match(msg, str(warning), re.I) and
+                issubclass(warning.__class__, cat)):
+                seen = True
+                reraise.remove(w)
+        if not seen and not quiet:
+            # This filter caught nothing
+            missing.append((msg, cat.__name__))
+    if reraise:
+        raise AssertionError("unhandled warning %s" % reraise[0])
+    if missing:
+        raise AssertionError("filter (%r, %s) did not catch any warning" %
+                             missing[0])
+
+
+@contextlib.contextmanager
+def save_restore_warnings_filters():
+    old_filters = warnings.filters[:]
+    try:
+        yield
+    finally:
+        warnings.filters[:] = old_filters
+
+
+def _warn_about_deprecation():
+    warnings.warn(
+        "This is used in test_support test to ensure"
+        " support.ignore_deprecations_from() works as expected."
+        " You should not be seeing this.",
+        DeprecationWarning,
+        stacklevel=0,
+    )
diff --git a/Lib/test/test_support.py b/Lib/test/test_support.py
index b5a16f9..60a7741 100644
--- a/Lib/test/test_support.py
+++ b/Lib/test/test_support.py
@@ -11,6 +11,8 @@ import tempfile
 import textwrap
 import time
 import unittest
+import warnings
+
 from test import support
 from test.support import script_helper
 from test.support import socket_helper
@@ -19,6 +21,33 @@ TESTFN = support.TESTFN
 
 
 class TestSupport(unittest.TestCase):
+    @classmethod
+    def setUpClass(cls):
+        orig_filter_len = len(warnings.filters)
+        cls._warnings_helper_token = support.ignore_deprecations_from(
+            "test.test_support", like=".*used in test_support.*"
+        )
+        cls._test_support_token = support.ignore_deprecations_from(
+            "test.test_support", like=".*You should NOT be seeing this.*"
+        )
+        assert len(warnings.filters) == orig_filter_len + 2
+
+    @classmethod
+    def tearDownClass(cls):
+        orig_filter_len = len(warnings.filters)
+        support.clear_ignored_deprecations(
+            cls._warnings_helper_token,
+            cls._test_support_token,
+        )
+        assert len(warnings.filters) == orig_filter_len - 2
+
+    def test_ignored_deprecations_are_silent(self):
+        """Test support.ignore_deprecations_from() silences warnings"""
+        with warnings.catch_warnings(record=True) as warning_objs:
+            _warn_about_deprecation()
+            warnings.warn("You should NOT be seeing this.", DeprecationWarning)
+            messages = [str(w.message) for w in warning_objs]
+        self.assertEqual(len(messages), 0, messages)
 
     def test_import_module(self):
         support.import_module("ftplib")
@@ -676,6 +705,17 @@ class TestSupport(unittest.TestCase):
     # SuppressCrashReport
 
 
+def _warn_about_deprecation():
+    # In 3.10+ this lives in test.support.warnings_helper
+    warnings.warn(
+        "This is used in test_support test to ensure"
+        " support.ignore_deprecations_from() works as expected."
+        " You should not be seeing this.",
+        DeprecationWarning,
+        stacklevel=0,
+    )
+
+
 def test_main():
     tests = [TestSupport]
     support.run_unittest(*tests)
diff --git a/Misc/NEWS.d/next/Tests/2021-08-06-18-36-04.bpo-44852.sUL8YX.rst b/Misc/NEWS.d/next/Tests/2021-08-06-18-36-04.bpo-44852.sUL8YX.rst
new file mode 100644
index 0000000..41b5c2f
--- /dev/null
+++ b/Misc/NEWS.d/next/Tests/2021-08-06-18-36-04.bpo-44852.sUL8YX.rst
@@ -0,0 +1,2 @@
+Add ability to wholesale silence DeprecationWarnings while running the
+regression test suite.