Bug Fix 708 - Union Iterability Checker

pyrefly/lib/alt/solve.rs

@@ -560,6 +560,12 @@ impl<'a, Ans: LookupAnswer> AnswersSolver<'a, Ans> {
         }
     }
 
+    fn is_iterable(&self, ty: &Type) -> bool {
+        self.unwrap_iterable(ty).is_some()
+            || matches!(ty, Type::Tuple(_))
+            || matches!(ty, Type::ClassType(cls) if self.as_tuple(cls).is_some())
+    }
+
     /// Given an `iterable` type, determine the iteration type; this is the type
     /// of `x` if we were to loop using `for x in iterable`.
     ///
@@ -584,7 +590,14 @@ impl<'a, Ans: LookupAnswer> AnswersSolver<'a, Ans> {
             }
             Type::Union(ts) => ts
                 .iter()
-                .flat_map(|t| self.iterate(t, range, errors))
+                .filter_map(|t| {
+                    if self.is_iterable(t) {
+                        Some(self.iterate(t, range, errors))
+                    } else {
+                        None
+                    }
+                })
+                .flatten()
                 .collect(),
             _ => {
                 let ty = self

pyrefly/lib/test/pattern_match.rs

@@ -60,3 +60,22 @@ def my_func(x: dict[MyEnumType, int]) -> int:
             return 0
 "#,
 );
+
+testcase!(
+    test_union_pattern_match_sequence,
+    r#"
+from typing import *
+
+class T: ...
+
+def my_func(x: T | tuple[T, T]):
+    match x:
+        case T(), T():  # Should not error: Type `T` is not iterable
+            print("Two T")
+        case T():
+            print("One T")
+
+my_func(T())
+my_func((T(), T()))
+"#,
+);