Support "is None" constraints from if statements during inference (#1189)

Co-authored-by: Marc Mueller <30130371+cdce8p@users.noreply.github.com>
Co-authored-by: Pierre Sassoulas <pierre.sassoulas@gmail.com>
Co-authored-by: Daniël van Noord <13665637+DanielNoord@users.noreply.github.com>

1 files changed, 20 insertions, 4 deletions

diff --git a/astroid/bases.py b/astroid/bases.py
index 2c047855..bf99ddce 100644
--- a/astroid/bases.py
+++ b/astroid/bases.py
@@ -11,7 +11,7 @@ import collections
 import collections.abc
 import sys
 from collections.abc import Sequence
-from typing import Any, ClassVar
+from typing import TYPE_CHECKING, Any, ClassVar
 
 from astroid import decorators, nodes
 from astroid.const import PY310_PLUS
@@ -35,6 +35,9 @@ if sys.version_info >= (3, 8):
 else:
     from typing_extensions import Literal
 
+if TYPE_CHECKING:
+    from astroid.constraint import Constraint
+
 objectmodel = lazy_import("interpreter.objectmodel")
 helpers = lazy_import("helpers")
 manager = lazy_import("manager")
@@ -146,11 +149,14 @@ def _infer_stmts(
 ) -> collections.abc.Generator[InferenceResult, None, None]:
     """Return an iterator on statements inferred by each statement in *stmts*."""
     inferred = False
+    constraint_failed = False
     if context is not None:
         name = context.lookupname
         context = context.clone()
+        constraints = context.constraints.get(name, {})
     else:
         name = None
+        constraints = {}
         context = InferenceContext()
 
     for stmt in stmts:
@@ -161,16 +167,26 @@ def _infer_stmts(
         # 'context' is always InferenceContext and Instances get '_infer_name' from ClassDef
         context.lookupname = stmt._infer_name(frame, name)  # type: ignore[union-attr]
         try:
+            stmt_constraints: set[Constraint] = set()
+            for constraint_stmt, potential_constraints in constraints.items():
+                if not constraint_stmt.parent_of(stmt):
+                    stmt_constraints.update(potential_constraints)
             # Mypy doesn't recognize that 'stmt' can't be Uninferable
             for inf in stmt.infer(context=context):  # type: ignore[union-attr]
-                yield inf
-                inferred = True
+                if all(constraint.satisfied_by(inf) for constraint in stmt_constraints):
+                    yield inf
+                    inferred = True
+                else:
+                    constraint_failed = True
         except NameInferenceError:
             continue
         except InferenceError:
             yield Uninferable
             inferred = True
-    if not inferred:
+
+    if not inferred and constraint_failed:
+        yield Uninferable
+    elif not inferred:
         raise InferenceError(
             "Inference failed for all members of {stmts!r}.",
             stmts=stmts,