Check subtyping when supertype is free type param

1 files changed, 24 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 1ff85fea..d86e0ed2 100644
--- a/src/test/java/org/shedlang/compiler/typechecker/TypeCheckerIsSubTypeTests.java
+++ b/src/test/java/org/shedlang/compiler/typechecker/TypeCheckerIsSubTypeTests.java
@@ -2,12 +2,15 @@ package org.shedlang.compiler.typechecker;
 
 import org.junit.jupiter.api.Test;
 import org.shedlang.compiler.sources.Sources;
+import org.shedlang.compiler.typechecker.errors.UnexpectedTypeError;
+import org.shedlang.compiler.typechecker.typesets.TypeSets;
 import org.shedlang.compiler.types.*;
 import org.shedlang.compiler.util.P;
 
 import java.util.List;
 import java.util.Map;
 
+import static org.junit.jupiter.api.Assertions.assertThrows;
 import static org.shedlang.compiler.typechecker.TypeCheckerSubTyping.isSubType;
 import static org.zwobble.precisely.AssertThat.assertThat;
 import static org.zwobble.precisely.Matchers.equalTo;
@@ -137,6 +140,27 @@ public class TypeCheckerIsSubTypeTests {
         )));
     }
 
+    @Test
+    public void whenSupertypeIsFreeTypeParamThenOtherTypesAreNotSubtype() {
+        var typeParam = TypeParam.forStructType(
+            Types.struct(NamespaceName.of("Example"), "Struct"),
+            "T"
+        );
+
+        var error = assertThrows(
+            UnexpectedTypeError.class,
+            () -> TypeCheckerSubTyping.addSubtypeConstraint(
+                Types.INT,
+                typeParam,
+                Sources.NULL,
+                TypeCheckerSubTyping.constraints(List.of(), TypeInfos.EMPTY)
+            )
+        );
+
+        assertThat(error.expected(), equalTo(TypeSets.type(typeParam)));
+        assertThat(error.actual(), equalTo(Types.INT));
+    }
+
     // == Sum types ==
 
     @Test