Update commonSupertype to consider sum types

1 files changed, 21 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 a30ecb24..1b9873a6 100644
--- a/src/test/java/org/shedlang/compiler/types/CommonSupertypeTests.java
+++ b/src/test/java/org/shedlang/compiler/types/CommonSupertypeTests.java
@@ -2,6 +2,7 @@ package org.shedlang.compiler.types;
 
 import org.junit.jupiter.api.Test;
 import org.shedlang.compiler.typechecker.TypeInfos;
+import org.shedlang.compiler.util.P;
 
 import java.util.List;
 
@@ -62,4 +63,24 @@ public class CommonSupertypeTests {
 
         assertThat(result, equalTo(Types.INT));
     }
+
+    @Test
+    public void commonSupertypeOfVariantsOfSameSumTypeIsThatSumType() {
+        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 result = Types.commonSupertype(
+            List.of(variantType1, variantType2),
+            typeInfos
+        );
+
+        assertThat(result, equalTo(sumType));
+    }
 }