Add subtyping between sum types

1 files changed, 23 insertions, 0 deletions

diff --git a/src/test/java/org/shedlang/compiler/typechecker/TypeCheckerIsSubTypeTests.java b/src/test/java/org/shedlang/compiler/typechecker/TypeCheckerIsSubTypeTests.java
index 580be580..d758cd96 100644
--- a/src/test/java/org/shedlang/compiler/typechecker/TypeCheckerIsSubTypeTests.java
+++ b/src/test/java/org/shedlang/compiler/typechecker/TypeCheckerIsSubTypeTests.java
@@ -196,6 +196,29 @@ public class TypeCheckerIsSubTypeTests {
     }
 
     @Test
+    public void sumTypeIsSubtypeOfOtherSumtypeIfVariantsAreSubsetOfOtherVariants() {
+        var namespaceName = NamespaceName.of("Example", "Project");
+        var sumType1 = Types.sum(namespaceName, "Sum1");
+        var sumType2 = Types.sum(namespaceName, "Sum2");
+        var variantType1 = Types.struct(namespaceName, "Variant1");
+        var variantType2 = Types.struct(namespaceName, "Variant2");
+        var variantType3 = Types.struct(namespaceName, "Variant3");
+        var typeInfos = TypeInfos.EMPTY
+            .addSumTypeInfo(sumType1, new SumTypeInfo(P.orderedSet(
+                variantType1,
+                variantType2
+            )))
+            .addSumTypeInfo(sumType2, new SumTypeInfo(P.orderedSet(
+                variantType1,
+                variantType2,
+                variantType3
+            )));
+
+        assertThat(isSubType(sumType1, sumType2, typeInfos), equalTo(true));
+        assertThat(isSubType(sumType2, sumType1, typeInfos), equalTo(false));
+    }
+
+    @Test
     public void variantWithoutTypeLevelArgIsSubTypeOfConstructedSumType() {
         var namespaceName = NamespaceName.of("Example", "Project");
         var sumType = Types.sum(namespaceName, "Sum");