Update commonSupertype to handle supertype of sum and its variants

1 files changed, 25 insertions, 0 deletions

diff --git a/src/test/java/org/shedlang/compiler/types/CommonSupertypeTests.java b/src/test/java/org/shedlang/compiler/types/CommonSupertypeTests.java
index 1b9873a6..fb9a14c5 100644
--- a/src/test/java/org/shedlang/compiler/types/CommonSupertypeTests.java
+++ b/src/test/java/org/shedlang/compiler/types/CommonSupertypeTests.java
@@ -83,4 +83,29 @@ public class CommonSupertypeTests {
 
         assertThat(result, equalTo(sumType));
     }
+
+    @Test
+    public void commonSupertypeOfSumTypeAndVariantOfThatSumTypeIsThatSumType() {
+        var namespaceName = NamespaceName.of("Example");
+        var variantType1 = Types.struct(namespaceName, "Variant1");
+        var variantType2 = Types.struct(namespaceName, "Variant2");
+        var sumType = Types.sum(namespaceName, "Sum");
+        var typeInfos = TypeInfos.EMPTY
+            .addSumTypeInfo(sumType, new SumTypeInfo(P.orderedSet(
+                variantType1,
+                variantType2
+            )));
+
+        var result1 = Types.commonSupertype(
+            List.of(sumType, variantType2),
+            typeInfos
+        );
+        var result2 = Types.commonSupertype(
+            List.of(variantType2, sumType),
+            typeInfos
+        );
+
+        assertThat(result1, equalTo(sumType));
+        assertThat(result2, equalTo(sumType));
+    }
 }