Limit inference to a maximum of 100 results at a time to prevent

spot performance issues.

Add new envrionment variable call ASTROID_MAX_INFERABLE to tune
the max inferable amount of values at a time.

Close pylint-dev#579
Close pylint-dev/pylint#2251

ChangeLog

@@ -157,6 +157,12 @@ Release Date: Unknown
 
  Close PyCQA/pylint#2159
 
+ * Limit the maximum amount of interable result in an NodeNG.infer() call to
+ 100 by default for performance issues with variables with large amounts of
+ possible values.
+ The max inferable value can be tuned by setting the ASTROID_MAX_INFERABLE environment
+ variable at start up.
+
 
 What's New in astroid 1.6.0?
 ============================

astroid/node_classes.py

@@ -323,7 +323,9 @@ def infer(self, context=None, **kwargs):
  if key in context.inferred:
  return iter(context.inferred[key])
 
- return context.cache_generator(key, self._infer(context, **kwargs))
+ gen = context.cache_generator(
+ key, self._infer(context, **kwargs))
+ return util.limit_inference(gen)
 
  def _repr_name(self):
  """Get a name for nice representation.

astroid/tests/unittest_inference.py

@@ -15,6 +15,7 @@
 import sys
 from functools import partial
 import unittest
+from unittest.mock import patch
 
 import pytest
 
@@ -4656,5 +4657,34 @@ def f(**kwargs):
  assert next(extract_node(code).infer()).as_string() == "{'f': 1}"
 
 
+def test_limit_inference_result_amount():
+ """Test setting limit inference result amount"""
+ code = """
+ args = []
+
+ if True:
+ args += ['a']
+
+ if True:
+ args += ['b']
+
+ if True:
+ args += ['c']
+
+ if True:
+ args += ['d']
+
+ args #@
+ """
+ result = extract_node(code).inferred()
+ assert len(result) == 16
+ with patch('astroid.util.MAX_INFERABLE', 4):
+ result_limited = extract_node(code).inferred()
+ # Can't guarentee exact size
+ assert len(result_limited) < 16
+ # Will not always be at the end
+ assert util.Uninferable in result_limited
+
+
 if __name__ == '__main__':
  unittest.main()

astroid/util.py

@@ -5,10 +5,12 @@
 # For details: https://github.com/PyCQA/astroid/blob/master/COPYING.LESSER
 
 import warnings
+import os
 
 import importlib
 import lazy_object_proxy
 
+MAX_INFERABLE = int(os.environ.get("ASTROID_MAX_INFERABLE", 100))
 
 def lazy_descriptor(obj):
  class DescriptorProxy(lazy_object_proxy.Proxy):
@@ -126,5 +128,20 @@ def proxy_alias(alias_name, node_type):
  return proxy(lambda: node_type)
 
 
+def limit_inference(iterable):
+ """Limit inference to MAX_INFERABLE
+
+ Limit inference amount to help with performance issues with
+ exponentially exploding possible results.
+ """
+ count = 0
+ for result in iterable:
+ count += 1
+ if count > MAX_INFERABLE:
+ yield Uninferable
+ return
+ yield result
+
+
 # Backwards-compatibility aliases
 YES = Uninferable