fixed return type using mesonbuild mypy-prime failure

Author: randolf-scholz

mypy/checker.py

@@ -8015,24 +8015,20 @@ def conditional_types(
             # attempt to narrow anything. Instead, we broaden the expr to Any to
             # avoid false positives
             return proposed_type, default
-        elif not any(  #  handle concrete subtypes
+        elif not any(
             type_range.is_upper_bound for type_range in proposed_type_ranges
-        ) and is_proper_subtype(current_type, proposed_type, ignore_promotions=True):
-            # Expression is always of one of the types in proposed_type_ranges
-            return default, UninhabitedType()
-        elif (  # handle structural subtypes
-            isinstance(proposed_type, CallableType)
-            or (isinstance(proposed_type, Instance) and proposed_type.type.is_protocol)
-        ) and is_subtype(current_type, proposed_type, ignore_promotions=True):
-            yes_type = default
-            no_type = (
-                None
-                if yes_type is None
-                else restrict_subtype_away(
-                    current_type, yes_type, consider_runtime_isinstance=consider_runtime_isinstance
+        ) and (  # concrete subtypes
+            is_proper_subtype(current_type, proposed_type, ignore_promotions=True)
+            or (  # structural subtypes
+                is_subtype(current_type, proposed_type, ignore_promotions=True)
+                and (
+                    isinstance(proposed_type, CallableType)
+                    or (isinstance(proposed_type, Instance) and proposed_type.type.is_protocol)
                 )
             )
-            return yes_type, no_type
+        ):
+            # Expression is always of one of the types in proposed_type_ranges
+            return default, UninhabitedType()
         elif not is_overlapping_types(current_type, proposed_type, ignore_promotions=True):
             # Expression is never of any type in proposed_type_ranges
             return UninhabitedType(), default

test-data/unit/check-isinstance.test

@@ -1086,6 +1086,21 @@ while bool():
     x + 'a'
 [builtins fixtures/isinstance.pyi]
 
+[case testUnreachableCode3]
+# flags: --warn-unreachable --python-version 3.10
+from collections.abc import Iterable
+
+class A: ...
+
+def test(dependencies: list[A] | None) -> None:
+    if dependencies is None:
+        dependencies = []
+    elif not isinstance(dependencies, Iterable):
+        dependencies = [dependencies]  # E: Statement is unreachable
+
+[builtins fixtures/isinstancelist.pyi]
+[typing fixtures/typing-full.pyi]
+
 [case testUnreachableWhileTrue]
 def f(x: int) -> None:
     while True: