Emit deprecations through WarningTemplate.warn; fix the instance #14931 missed

changelog/15137.bugfix.rst

@@ -0,0 +1 @@
+The deprecation warning for passing a non-string value to a ``string``-typed ini option no longer reuses one warning instance, so it no longer accumulates traceback frames when warnings are turned into errors -- the case :issue:`14912` fixed for the other deprecations.

src/_pytest/config/__init__.py

@@ -301,11 +301,9 @@ def console_main() -> int:
         This function is slated for removal in pytest 10.
         It is not meant for programmable use; use :func:`pytest.main` instead.
     """
-    import warnings
-
     from _pytest.deprecated import CONSOLE_MAIN
 
-    warnings.warn(CONSOLE_MAIN.format(), stacklevel=2)
+    CONSOLE_MAIN.warn(stacklevel=2)
     return _console_main()
 
 
@@ -1283,10 +1281,7 @@ def inicfg(self) -> _DeprecatedInicfgProxy:
 
         @property
         def inicfg(self) -> _DeprecatedInicfgProxy:
-            warnings.warn(
-                _pytest.deprecated.CONFIG_INICFG.format(),
-                stacklevel=2,
-            )
+            _pytest.deprecated.CONFIG_INICFG.warn(stacklevel=2)
             return _DeprecatedInicfgProxy(self)
 
     @property
@@ -2052,10 +2047,7 @@ def _getini_ini(
             return _strtobool(str(value).strip())
         elif type == "string":
             if not isinstance(value, str):
-                warnings.warn(
-                    _pytest.deprecated.INI_STRING_TYPE_NON_STR_VALUE,
-                    stacklevel=2,
-                )
+                _pytest.deprecated.INI_STRING_TYPE_NON_STR_VALUE.warn(stacklevel=2)
             return value
         elif type == "int":
             if not isinstance(value, str):

src/_pytest/deprecated.py

@@ -5,19 +5,16 @@
 be removed when the time comes.
 
 All constants defined in this module should be instances of
-:class:`UnformattedWarning`, whose ``format`` method returns a fresh warning
-instance each time. Do not warn with shared warning instances: if a warning is
-raised as an error, CPython appends to the exception's existing ``__traceback__``,
-so a process-lifetime instance would accumulate stale frames from previous raises.
+:class:`WarningTemplate`. Emit them with its ``warn`` method, or pass the fresh
+instance from ``format`` to an API that takes a warning; see its docstring for
+why a warning instance is never kept around.
 """
 
 from __future__ import annotations
 
-from warnings import warn
-
 from _pytest.warning_types import PytestDeprecationWarning
 from _pytest.warning_types import PytestRemovedIn10Warning
-from _pytest.warning_types import UnformattedWarning
+from _pytest.warning_types import WarningTemplate
 
 
 # set of plugins which have been integrated into the core; we use this list to ignore
@@ -31,13 +28,13 @@
 
 
 # This could have been removed pytest 8, but it's harmless and common, so no rush to remove.
-YIELD_FIXTURE = UnformattedWarning(
+YIELD_FIXTURE = WarningTemplate(
     PytestRemovedIn10Warning,
     "@pytest.yield_fixture is deprecated.\n"
     "Use @pytest.fixture instead; they are the same.",
 )
 
-CLASS_FIXTURE_INSTANCE_METHOD = UnformattedWarning(
+CLASS_FIXTURE_INSTANCE_METHOD = WarningTemplate(
     PytestRemovedIn10Warning,
     "{scope}-scoped fixtures defined as instance methods are deprecated.\n"
     "Instance attributes set in the {fixturename!r} fixture will NOT be visible to test methods,\n"
@@ -47,13 +44,13 @@
 )
 
 # This deprecation is never really meant to be removed.
-PRIVATE = UnformattedWarning(
+PRIVATE = WarningTemplate(
     PytestDeprecationWarning,
     "A private pytest class or function was used.",
 )
 
 
-HOOK_LEGACY_MARKING = UnformattedWarning(
+HOOK_LEGACY_MARKING = WarningTemplate(
     PytestRemovedIn10Warning,
     "The hook{type} {fullname} uses old-style configuration options (marks or attributes).\n"
     "Please use the pytest.hook{type}({hook_opts}) decorator instead\n"
@@ -62,56 +59,57 @@
     "#configuring-hook-specs-impls-using-markers",
 )
 
-MONKEYPATCH_LEGACY_NAMESPACE_PACKAGES = UnformattedWarning(
+MONKEYPATCH_LEGACY_NAMESPACE_PACKAGES = WarningTemplate(
     PytestRemovedIn10Warning,
     "monkeypatch.syspath_prepend() called with pkg_resources legacy namespace packages detected.\n"
     "Legacy namespace packages (using pkg_resources.declare_namespace) are deprecated.\n"
     "Please use native namespace packages (PEP 420) instead.\n"
     "See https://docs.pytest.org/en/stable/deprecations.html#monkeypatch-fixup-namespace-packages",
 )
 
-PARAMETRIZE_NON_COLLECTION_ITERABLE = UnformattedWarning(
+PARAMETRIZE_NON_COLLECTION_ITERABLE = WarningTemplate(
     PytestRemovedIn10Warning,
     "Passing a non-Collection iterable to parametrize is deprecated.\n"
     "Test: {nodeid}, argvalues type: {type_name}\n"
     "Please convert to a list or tuple.\n"
     "See https://docs.pytest.org/en/stable/deprecations.html#parametrize-iterators",
 )
 
-CONSOLE_MAIN = UnformattedWarning(
+CONSOLE_MAIN = WarningTemplate(
     PytestRemovedIn10Warning,
     "pytest.console_main() is deprecated and will be removed in pytest 10.\n"
     "It was never intended for programmatic use; use pytest.main() instead.\n"
     "See https://docs.pytest.org/en/stable/deprecations.html#console-main",
 )
 
-CONFIG_INICFG = UnformattedWarning(
+CONFIG_INICFG = WarningTemplate(
     PytestRemovedIn10Warning,
     "config.inicfg is deprecated, use config.getini() to access configuration values instead.\n"
     "See https://docs.pytest.org/en/stable/deprecations.html#config-inicfg",
 )
 
-FIXTURE_GETFIXTUREVALUE_DURING_TEARDOWN = UnformattedWarning(
+FIXTURE_GETFIXTUREVALUE_DURING_TEARDOWN = WarningTemplate(
     PytestRemovedIn10Warning,
     'Calling request.getfixturevalue("{argname}") during teardown is deprecated.\n'
     "Please request the fixture before teardown begins, either by declaring it in the fixture signature "
     "or by calling request.getfixturevalue() before the fixture yields.\n"
     "See https://docs.pytest.org/en/stable/deprecations.html#dynamic-fixture-request-during-teardown",
 )
 
-PASTEBIN = UnformattedWarning(
+PASTEBIN = WarningTemplate(
     PytestRemovedIn10Warning,
     "The --pastebin option is deprecated. "
     "The functionality is now available in an external plugin package, pytest-pastebin.\n"
     "See https://docs.pytest.org/en/stable/deprecations.html#the-pastebin-option",
 )
 
-INI_STRING_TYPE_NON_STR_VALUE = PytestRemovedIn10Warning(
+INI_STRING_TYPE_NON_STR_VALUE = WarningTemplate(
+    PytestRemovedIn10Warning,
     "Passing a value that is not a string to a 'string'-typed ini option is deprecated.\n"
     "In a future version this will raise a TypeError, matching the behavior of the "
     "corresponding TOML config path.\n"
     "If your plugin intentionally accepts non-string values, declare an explicit type "
-    '(e.g. type="args") instead of relying on the implicit string default.'
+    '(e.g. type="args") instead of relying on the implicit string default.',
 )
 
 # You want to make some `__init__` or function "private".
@@ -133,30 +131,30 @@
 # the warning (possibly error in the future).
 
 
-FIXTURE_BASEID_DEPRECATED = UnformattedWarning(
+FIXTURE_BASEID_DEPRECATED = WarningTemplate(
     PytestRemovedIn10Warning,
     "Passing baseid to FixtureDef is deprecated. Pass node instead for fixture scoping.",
 )
 
-FIXTURE_NODEID_DEPRECATED = UnformattedWarning(
+FIXTURE_NODEID_DEPRECATED = WarningTemplate(
     PytestRemovedIn10Warning,
     "Passing nodeid to _register_fixture is deprecated. "
     "Pass node instead for fixture scoping.",
 )
 
-FIXTUREDEF_HAS_LOCATION_DEPRECATED = UnformattedWarning(
+FIXTUREDEF_HAS_LOCATION_DEPRECATED = WarningTemplate(
     PytestRemovedIn10Warning,
     "FixtureDef.has_location is deprecated and will be removed in pytest 10. "
     "See https://docs.pytest.org/en/stable/deprecations.html#fixturedef-has-location-deprecated",
 )
 
-PARSEFACTORIES_NODEID_DEPRECATED = UnformattedWarning(
+PARSEFACTORIES_NODEID_DEPRECATED = WarningTemplate(
     PytestRemovedIn10Warning,
     "Passing nodeid string to parsefactories is deprecated. "
     "Use parsefactories(holder=obj, node=node) instead.",
 )
 
-CALLSPEC2_RENAMED = UnformattedWarning(
+CALLSPEC2_RENAMED = WarningTemplate(
     PytestRemovedIn10Warning,
     "_pytest.python.CallSpec2 has been renamed to CallSpec.\n"
     "The CallSpec2 alias will be removed in pytest 10.\n"
@@ -167,4 +165,4 @@
 
 def check_ispytest(ispytest: bool) -> None:
     if not ispytest:
-        warn(PRIVATE.format(), stacklevel=3)
+        PRIVATE.warn(stacklevel=3)

src/_pytest/fixtures.py

@@ -30,7 +30,6 @@
 from typing import overload
 from typing import TYPE_CHECKING
 from typing import TypeVar
-import warnings
 
 import _pytest
 from _pytest import nodes
@@ -777,10 +776,7 @@ def _get_active_fixturedef(self, argname: str) -> FixtureDef[object]:
         if not self.session._setupstate.is_node_active(self.node):
             # TODO(pytest10.1): Remove the `warn` and `if` and call
             # _raise_teardown_lookup_error unconditionally.
-            warnings.warn(
-                FIXTURE_GETFIXTUREVALUE_DURING_TEARDOWN.format(argname=argname),
-                stacklevel=3,
-            )
+            FIXTURE_GETFIXTUREVALUE_DURING_TEARDOWN.warn(stacklevel=3, argname=argname)
             if subrequest.node not in self.session._setupstate.stack:
                 self._raise_teardown_lookup_error(argname)
 
@@ -1132,7 +1128,7 @@ def __init__(
         check_ispytest(_ispytest)
         # Emit deprecation warning if deprecated baseid string is used.
         if node is NOTSET:
-            warnings.warn(FIXTURE_BASEID_DEPRECATED.format(), stacklevel=2)
+            FIXTURE_BASEID_DEPRECATED.warn(stacklevel=2)
         if baseid is NOTSET:
             baseid = None
         # The node where this fixture was defined, if available.
@@ -1197,7 +1193,7 @@ def scope(self) -> ScopeName:
 
     @property
     def has_location(self) -> bool:
-        warnings.warn(FIXTUREDEF_HAS_LOCATION_DEPRECATED.format(), stacklevel=2)
+        FIXTUREDEF_HAS_LOCATION_DEPRECATED.warn(stacklevel=2)
         return self._has_location
 
     def addfinalizer(self, finalizer: Callable[[], object]) -> None:
@@ -1350,12 +1346,10 @@ def __tracebackhide__(e):
             # classmethod: bound_to is the class itself (a type)
             # instance method: bound_to is an instance (not a type)
             if not isinstance(bound_to, type):
-                warnings.warn(
-                    CLASS_FIXTURE_INSTANCE_METHOD.format(
-                        scope=fixturedef._scope.name.capitalize(),
-                        fixturename=request.fixturename,
-                    ),
+                CLASS_FIXTURE_INSTANCE_METHOD.warn(
                     stacklevel=2,
+                    scope=fixturedef._scope.name.capitalize(),
+                    fixturename=request.fixturename,
                 )
 
     if instance is not None:
@@ -1620,7 +1614,7 @@ def yield_fixture(
     .. deprecated:: 3.0
         Use :py:func:`pytest.fixture` directly instead.
     """
-    warnings.warn(YIELD_FIXTURE.format(), stacklevel=2)
+    YIELD_FIXTURE.warn(stacklevel=2)
     return fixture(
         fixture_function,
         *args,
@@ -2091,7 +2085,7 @@ def _register_fixture(
         """
         # Emit deprecation warning if nodeid string.
         if nodeid is not NOTSET or node is NOTSET:
-            warnings.warn(FIXTURE_NODEID_DEPRECATED.format(), stacklevel=2)
+            FIXTURE_NODEID_DEPRECATED.warn(stacklevel=2)
         fixture_def = FixtureDef(
             config=self.config,
             baseid=nodeid,
@@ -2280,7 +2274,7 @@ def parsefactories(
             raise TypeError("parsefactories() requires holder or node_or_obj")
         elif nodeid is not NOTSET:
             # Legacy: parsefactories(obj, nodeid) - string-based scoping only.
-            warnings.warn(PARSEFACTORIES_NODEID_DEPRECATED.format(), stacklevel=2)
+            PARSEFACTORIES_NODEID_DEPRECATED.warn(stacklevel=2)
             holderobj = node_or_obj
             effective_nodeid = nodeid
         else:

src/_pytest/mark/structures.py

@@ -202,12 +202,10 @@ def _for_parametrize(
         nodeid: str,
     ) -> tuple[Sequence[str], list[ParameterSet]]:
         if not isinstance(argvalues, Collection):
-            warnings.warn(
-                PARAMETRIZE_NON_COLLECTION_ITERABLE.format(
-                    nodeid=nodeid,
-                    type_name=type(argvalues).__name__,
-                ),
+            PARAMETRIZE_NON_COLLECTION_ITERABLE.warn(
                 stacklevel=3,
+                nodeid=nodeid,
+                type_name=type(argvalues).__name__,
             )
 
         argnames, force_tuple = cls._parse_parametrize_args(argnames, argvalues)

src/_pytest/monkeypatch.py

@@ -384,9 +384,7 @@ def syspath_prepend(self, path) -> None:
                         continue
                     ns_pkg_path = path_obj / ns_pkg.replace(".", os.sep)
                     if ns_pkg_path.is_dir():
-                        warnings.warn(
-                            MONKEYPATCH_LEGACY_NAMESPACE_PACKAGES.format(), stacklevel=2
-                        )
+                        MONKEYPATCH_LEGACY_NAMESPACE_PACKAGES.warn(stacklevel=2)
                         break
 
             fixup_namespace_packages(str(path))

src/_pytest/python.py

@@ -1852,6 +1852,6 @@ def runtest(self) -> None:
 
 def __getattr__(name: str) -> object:
     if name == "CallSpec2":
-        warnings.warn(CALLSPEC2_RENAMED.format(), stacklevel=2)
+        CALLSPEC2_RENAMED.warn(stacklevel=2)
         return CallSpec
     raise AttributeError(f"module {__name__!r} has no attribute {name!r}")

src/_pytest/warning_types.py

@@ -118,21 +118,48 @@ class PytestUnhandledThreadExceptionWarning(PytestWarning):
 
 
 @final
-@dataclasses.dataclass
-class UnformattedWarning(Generic[_W]):
-    """A warning meant to be formatted during runtime.
-
-    This is used to hold warnings that need to format their message at runtime,
-    as opposed to a direct message.
+@dataclasses.dataclass(frozen=True)
+class WarningTemplate(Generic[_W]):
+    """A warning category paired with its message template.
+
+    Emitting a warning goes through this type so that a *fresh* warning instance
+    is built every time.
+
+    Warning instances must never be kept around and reused: under an ``error``
+    filter ``warnings.warn(instance)`` raises that very object, so CPython
+    appends to its existing ``__traceback__`` instead of replacing it, and
+    ``__context__`` picks up whatever exception happened to be in flight. A
+    shared instance therefore grows a traceback without bound, pins the locals
+    of unrelated frames, and shows frames of earlier, unrelated code in failure
+    reports (#14912).
     """
 
     category: type[_W]
     template: str
 
     def format(self, **kwargs: Any) -> _W:
-        """Return an instance of the warning category, formatted with given kwargs."""
+        """Return a new instance of the warning category.
+
+        The template is only run through :meth:`str.format` when ``kwargs`` are
+        given, so constant messages may contain literal braces unescaped.
+        """
+        if not kwargs:
+            return self.category(self.template)
         return self.category(self.template.format(**kwargs))
 
+    def warn(self, *, stacklevel: int = 1, **kwargs: Any) -> None:
+        """Emit the warning, with ``stacklevel`` relative to the caller.
+
+        The extra level compensates for this method's own frame, so callers pass
+        the same ``stacklevel`` they would pass to :func:`warnings.warn`.
+        """
+        __tracebackhide__ = True
+        warnings.warn(self.format(**kwargs), stacklevel=stacklevel + 1)
+
+
+#: Kept for third-party code that reached into this private module.
+UnformattedWarning = WarningTemplate
+
 
 @final
 class PytestApproxDecimalToleranceWarning(PytestWarning):