Stop testing iterables for truthiness!

Author: sterliakov

mypy/solve.py

@@ -270,6 +270,7 @@ def solve_one(lowers: Iterable[Type], uppers: Iterable[Type]) -> Type | None:
     uppers = new_uppers
 
     # ...unless this is the only information we have, then we just pass it on.
+    lowers = list(lowers)
     if not uppers and not lowers:
         candidate = UninhabitedType()
         candidate.ambiguous = True
@@ -285,7 +286,7 @@ def solve_one(lowers: Iterable[Type], uppers: Iterable[Type]) -> Type | None:
         # This deviates from the general mypy semantics because
         # recursive types are union-heavy in 95% of cases.
         # Retain `None` when no bottoms were provided to avoid bogus `Never` inference.
-        bottom = UnionType.make_union(list(lowers))
+        bottom = UnionType.make_union(lowers)
     else:
         # The order of lowers is non-deterministic.
         # We attempt to sort lowers because joins are non-associative. For instance: