Limit expensive decorator function (#1407)

Author: cdce8p

ChangeLog

@@ -61,6 +61,11 @@ Release date: TBA
 * Fix ``ClassDef.fromlineno``. For Python < 3.8 the ``lineno`` attribute includes decorators.
   ``fromlineno`` should return the line of the ``class`` statement itself.
 
+* Performance improvements. Only run expensive decorator functions when
+  non-default Deprecation warnings are enabled, eg. during a Pytest run.
+
+  Closes #1383
+
 What's New in astroid 2.9.4?
 ============================
 Release date: TBA

astroid/decorators.py

@@ -152,58 +152,79 @@ def raise_if_nothing_inferred(func, instance, args, kwargs):
     yield from generator
 
 
-def deprecate_default_argument_values(
-    astroid_version: str = "3.0", **arguments: str
-) -> Callable[[Callable[P, R]], Callable[P, R]]:
-    """Decorator which emitts a DeprecationWarning if any arguments specified
-    are None or not passed at all.
-
-    Arguments should be a key-value mapping, with the key being the argument to check
-    and the value being a type annotation as string for the value of the argument.
-    """
-    # Helpful links
-    # Decorator for DeprecationWarning: https://stackoverflow.com/a/49802489
-    # Typing of stacked decorators: https://stackoverflow.com/a/68290080
-
-    def deco(func: Callable[P, R]) -> Callable[P, R]:
-        """Decorator function."""
-
-        @functools.wraps(func)
-        def wrapper(*args: P.args, **kwargs: P.kwargs) -> R:
-            """Emit DeprecationWarnings if conditions are met."""
-
-            keys = list(inspect.signature(func).parameters.keys())
-            for arg, type_annotation in arguments.items():
-                try:
-                    index = keys.index(arg)
-                except ValueError:
-                    raise Exception(
-                        f"Can't find argument '{arg}' for '{args[0].__class__.__qualname__}'"
-                    ) from None
-                if (
-                    # Check kwargs
-                    # - if found, check it's not None
-                    (arg in kwargs and kwargs[arg] is None)
-                    # Check args
-                    # - make sure not in kwargs
-                    # - len(args) needs to be long enough, if too short
-                    #   arg can't be in args either
-                    # - args[index] should not be None
-                    or arg not in kwargs
-                    and (
-                        index == -1
-                        or len(args) <= index
-                        or (len(args) > index and args[index] is None)
-                    )
-                ):
-                    warnings.warn(
-                        f"'{arg}' will be a required argument for "
-                        f"'{args[0].__class__.__qualname__}.{func.__name__}' in astroid {astroid_version} "
-                        f"('{arg}' should be of type: '{type_annotation}')",
-                        DeprecationWarning,
-                    )
-            return func(*args, **kwargs)
-
-        return wrapper
-
-    return deco
+# Expensive decorators only used to emit Deprecation warnings.
+# If no other than the default DeprecationWarning are enabled,
+# fall back to passthrough implementations.
+if util.check_warnings_filter():
+
+    def deprecate_default_argument_values(
+        astroid_version: str = "3.0", **arguments: str
+    ) -> Callable[[Callable[P, R]], Callable[P, R]]:
+        """Decorator which emits a DeprecationWarning if any arguments specified
+        are None or not passed at all.
+
+        Arguments should be a key-value mapping, with the key being the argument to check
+        and the value being a type annotation as string for the value of the argument.
+
+        To improve performance, only used when DeprecationWarnings other than
+        the default one are enabled.
+        """
+        # Helpful links
+        # Decorator for DeprecationWarning: https://stackoverflow.com/a/49802489
+        # Typing of stacked decorators: https://stackoverflow.com/a/68290080
+
+        def deco(func: Callable[P, R]) -> Callable[P, R]:
+            """Decorator function."""
+
+            @functools.wraps(func)
+            def wrapper(*args: P.args, **kwargs: P.kwargs) -> R:
+                """Emit DeprecationWarnings if conditions are met."""
+
+                keys = list(inspect.signature(func).parameters.keys())
+                for arg, type_annotation in arguments.items():
+                    try:
+                        index = keys.index(arg)
+                    except ValueError:
+                        raise Exception(
+                            f"Can't find argument '{arg}' for '{args[0].__class__.__qualname__}'"
+                        ) from None
+                    if (
+                        # Check kwargs
+                        # - if found, check it's not None
+                        (arg in kwargs and kwargs[arg] is None)
+                        # Check args
+                        # - make sure not in kwargs
+                        # - len(args) needs to be long enough, if too short
+                        #   arg can't be in args either
+                        # - args[index] should not be None
+                        or arg not in kwargs
+                        and (
+                            index == -1
+                            or len(args) <= index
+                            or (len(args) > index and args[index] is None)
+                        )
+                    ):
+                        warnings.warn(
+                            f"'{arg}' will be a required argument for "
+                            f"'{args[0].__class__.__qualname__}.{func.__name__}' in astroid {astroid_version} "
+                            f"('{arg}' should be of type: '{type_annotation}')",
+                            DeprecationWarning,
+                        )
+                return func(*args, **kwargs)
+
+            return wrapper
+
+        return deco
+
+else:
+
+    def deprecate_default_argument_values(
+        astroid_version: str = "3.0", **arguments: str
+    ) -> Callable[[Callable[P, R]], Callable[P, R]]:
+        """Passthrough decorator to improve performance if DeprecationWarnings are disabled."""
+
+        def deco(func: Callable[P, R]) -> Callable[P, R]:
+            """Decorator function."""
+            return func
+
+        return deco

astroid/util.py

@@ -140,3 +140,16 @@ def proxy_alias(alias_name, node_type):
         },
     )
     return proxy(lambda: node_type)
+
+
+def check_warnings_filter() -> bool:
+    """Return True if any other than the default DeprecationWarning filter is enabled.
+
+    https://docs.python.org/3/library/warnings.html#default-warning-filter
+    """
+    return any(
+        issubclass(DeprecationWarning, filter[2])
+        and filter[0] != "ignore"
+        and filter[3] != "__main__"
+        for filter in warnings.filters
+    )