Update commonSubtype() to produce more specific types

1 files changed, 45 insertions, 6 deletions

diff --git a/src/test/java/org/shedlang/compiler/types/CommonSubtypeTests.java b/src/test/java/org/shedlang/compiler/types/CommonSubtypeTests.java
index 9095ca07..a5e030e5 100644
--- a/src/test/java/org/shedlang/compiler/types/CommonSubtypeTests.java
+++ b/src/test/java/org/shedlang/compiler/types/CommonSubtypeTests.java
@@ -1,6 +1,8 @@
 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;
 
@@ -10,43 +12,80 @@ import static org.zwobble.precisely.Matchers.equalTo;
 public class CommonSubtypeTests {
     @Test
     public void commonSubtypeOfNoTypesIsTop() {
-        var result = Types.commonSubtype(List.of());
+        var result = Types.commonSubtype(List.of(), TypeInfos.EMPTY);
 
         assertThat(result, equalTo(Types.TOP));
     }
 
     @Test
     public void commonSubtypeOfSingleTypeIsThatType() {
-        var result = Types.commonSubtype(List.of(Types.INT));
+        var result = Types.commonSubtype(List.of(Types.INT), TypeInfos.EMPTY);
 
         assertThat(result, equalTo(Types.INT));
     }
 
     @Test
     public void commonSubtypeOfRepeatedTypeIsThatType() {
-        var result = Types.commonSubtype(List.of(Types.INT, Types.INT, Types.INT));
+        var result = Types.commonSubtype(
+            List.of(Types.INT, Types.INT, Types.INT),
+            TypeInfos.EMPTY
+        );
 
         assertThat(result, equalTo(Types.INT));
     }
 
     @Test
     public void commonSubtypeOfUnrelatedTypesIsBottom() {
-        var result = Types.commonSubtype(List.of(Types.INT, Types.STRING));
+        var result = Types.commonSubtype(
+            List.of(Types.INT, Types.STRING),
+            TypeInfos.EMPTY
+        );
 
         assertThat(result, equalTo(Types.BOTTOM));
     }
 
     @Test
     public void commonSubtypeOfTopAndOtherTypeIsOtherType() {
-        var result = Types.commonSubtype(List.of(Types.TOP, Types.INT));
+        var result = Types.commonSubtype(
+            List.of(Types.TOP, Types.INT),
+            TypeInfos.EMPTY
+        );
 
         assertThat(result, equalTo(Types.INT));
     }
 
     @Test
     public void commonSubtypeOfOtherTypeAndTopIsOtherType() {
-        var result = Types.commonSubtype(List.of(Types.INT, Types.TOP));
+        var result = Types.commonSubtype(
+            List.of(Types.INT, Types.TOP),
+            TypeInfos.EMPTY
+        );
 
         assertThat(result, equalTo(Types.INT));
     }
+
+    @Test
+    public void commonSubtypeOfSumTypeAndVariantOfThatSumTypeIsThatVariant() {
+        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.commonSubtype(
+            List.of(sumType, variantType2),
+            typeInfos
+        );
+        var result2 = Types.commonSubtype(
+            List.of(variantType2, sumType),
+            typeInfos
+        );
+
+        assertThat(result1, equalTo(variantType2));
+        assertThat(result2, equalTo(variantType2));
+    }
 }