[mypyc] Fixing iteration over NamedTuple objects. (#18254)

Fixes mypyc/mypyc#1063.

Adding elif-blocks for getting RType of items in classes derived from
`NamedTuple`.

Author: advait-dixit

mypyc/irbuild/builder.py

@@ -52,6 +52,7 @@
     Type,
     TypedDictType,
     TypeOfAny,
+    TypeVarLikeType,
     UninhabitedType,
     UnionType,
     get_proper_type,
@@ -926,11 +927,22 @@ def get_sequence_type_from_type(self, target_type: Type) -> RType:
             return RUnion.make_simplified_union(
                 [self.get_sequence_type_from_type(item) for item in target_type.items]
             )
-        assert isinstance(target_type, Instance), target_type
-        if target_type.type.fullname == "builtins.str":
-            return str_rprimitive
-        else:
-            return self.type_to_rtype(target_type.args[0])
+        elif isinstance(target_type, Instance):
+            if target_type.type.fullname == "builtins.str":
+                return str_rprimitive
+            else:
+                return self.type_to_rtype(target_type.args[0])
+        # This elif-blocks are needed for iterating over classes derived from NamedTuple.
+        elif isinstance(target_type, TypeVarLikeType):
+            return self.get_sequence_type_from_type(target_type.upper_bound)
+        elif isinstance(target_type, TupleType):
+            # Tuple might have elements of different types.
+            rtypes = {self.mapper.type_to_rtype(item) for item in target_type.items}
+            if len(rtypes) == 1:
+                return rtypes.pop()
+            else:
+                return RUnion.make_simplified_union(list(rtypes))
+        assert False, target_type
 
     def get_dict_base_type(self, expr: Expression) -> list[Instance]:
         """Find dict type of a dict-like expression.

mypyc/test-data/run-loops.test

@@ -545,3 +545,29 @@ def test_range_object() -> None:
         r4 = range(4, 12, 0)
     except ValueError as e:
         assert "range() arg 3 must not be zero" in str(e)
+
+[case testNamedTupleLoop]
+from collections.abc import Iterable
+from typing import NamedTuple, Any
+from typing_extensions import Self
+
+
+class Vector2(NamedTuple):
+    x: int
+    y: float
+
+    @classmethod
+    def from_iter(cls, iterable: Iterable[Any]) -> Self:
+        return cls(*iter(iterable))
+
+    def __neg__(self) -> Self:
+        return self.from_iter(-c for c in self)
+
+[file driver.py]
+import native
+print(-native.Vector2(2, -3.1))
+print([x for x in native.Vector2(4, -5.2)])
+
+[out]
+Vector2(x=-2, y=3.1)
+\[4, -5.2]