Removed mutable default value in _inference_tip_cache (#1139)

* Removed mutable default value in _inference_tip_cache

The mutable default is problematic when astroid is used as a library,
because it effectively becomes a memory leak, see #792.

This commit moves the cache to the global namespace and adds a public
API entry point to clear it.

* Removed the itertools.tee call from _inference_tip_cached

This commit is not expected to affect the behavior, and if anything, should
improve memory usage, because result is only materilized once (before it was
also stored in-full inside itertools.tee).

ChangeLog

@@ -23,6 +23,8 @@ What's New in astroid 2.7.2?
 Release date: 2021-08-20
 
 * ``BaseContainer`` is now public, and will replace ``_BaseContainer`` completely in astroid 3.0.
+* The call cache used by inference functions produced by ``inference_tip``
+  can now be cleared via ``clear_inference_tip_cache``.
 
 * ``astroid.const.BUILTINS`` and ``astroid.bases.BUILTINS`` are not used internally anymore
   and will be removed in astroid 3.0. Simply replace this by the string 'builtins' for better

astroid/inference_tip.py

@@ -3,36 +3,35 @@
 
 """Transform utilities (filters and decorator)"""
 
-import itertools
 import typing
 
 import wrapt
 
-# pylint: disable=dangerous-default-value
 from astroid.exceptions import InferenceOverwriteError
 from astroid.nodes import NodeNG
 
+InferFn = typing.Callable[..., typing.Any]
+
+_cache: typing.Dict[typing.Tuple[InferFn, NodeNG], typing.Any] = {}
+
+
+def clear_inference_tip_cache():
+    """Clear the inference tips cache."""
+    _cache.clear()
+
 
 @wrapt.decorator
-def _inference_tip_cached(func, instance, args, kwargs, _cache={}):  # noqa:B006
+def _inference_tip_cached(func, instance, args, kwargs):
     """Cache decorator used for inference tips"""
     node = args[0]
     try:
-        return iter(_cache[func, node])
+        result = _cache[func, node]
     except KeyError:
-        result = func(*args, **kwargs)
-        # Need to keep an iterator around
-        original, copy = itertools.tee(result)
-        _cache[func, node] = list(copy)
-        return original
-
-
-# pylint: enable=dangerous-default-value
+        result = _cache[func, node] = list(func(*args, **kwargs))
+    return iter(result)
 
 
-def inference_tip(
-    infer_function: typing.Callable, raise_on_overwrite: bool = False
-) -> typing.Callable:
+def inference_tip(infer_function: InferFn, raise_on_overwrite: bool = False) -> InferFn:
     """Given an instance specific inference function, return a function to be
     given to AstroidManager().register_transform to set this inference function.
 
@@ -54,9 +53,7 @@ def inference_tip(
         excess overwrites.
     """
 
-    def transform(
-        node: NodeNG, infer_function: typing.Callable = infer_function
-    ) -> NodeNG:
+    def transform(node: NodeNG, infer_function: InferFn = infer_function) -> NodeNG:
         if (
             raise_on_overwrite
             and node._explicit_inference is not None