``safe_infer`` can infer a value as long as all the paths share the same type.

This permits finding more errors for functions whose return values use the
same type. Until now we were stopping after the first inference result if we
detected that a node value had multiple possible results.

Close #2503

1 files changed, 21 insertions, 6 deletions

diff --git a/pylint/checkers/utils.py b/pylint/checkers/utils.py
index 4bda9ff78..41b3876cb 100644
--- a/pylint/checkers/utils.py
+++ b/pylint/checkers/utils.py
@@ -1075,6 +1075,13 @@ def supports_delitem(value: astroid.node_classes.NodeNG) -> bool:
     return _supports_protocol(value, _supports_delitem_protocol)
 
 
+def _get_python_type_of_node(node):
+    pytype = getattr(node, "pytype", None)
+    if callable(pytype):
+        return pytype()
+    return None
+
+
 @lru_cache(maxsize=1024)
 def safe_infer(
     node: astroid.node_classes.NodeNG, context=None
@@ -1082,20 +1089,28 @@ def safe_infer(
     """Return the inferred value for the given node.
 
     Return None if inference failed or if there is some ambiguity (more than
-    one node has been inferred).
+    one node has been inferred of different types).
     """
+    inferred_types = set()
     try:
-        inferit = node.infer(context=context)
-        value = next(inferit)
+        infer_gen = node.infer(context=context)
+        value = next(infer_gen)
     except astroid.InferenceError:
         return None
+
+    if value is not astroid.Uninferable:
+        inferred_types.add(_get_python_type_of_node(value))
+
     try:
-        next(inferit)
-        return None  # None if there is ambiguity on the inferred node
+        for inferred in infer_gen:
+            inferred_type = _get_python_type_of_node(inferred)
+            if inferred_type not in inferred_types:
+                return None  # If there is ambiguity on the inferred node.
     except astroid.InferenceError:
-        return None  # there is some kind of ambiguity
+        return None  # There is some kind of ambiguity
     except StopIteration:
         return value
+    return value if len(inferred_types) <= 1 else None
 
 
 def has_known_bases(klass: astroid.ClassDef, context=None) -> bool: