Throw better error when value is not type

5 files changed, 74 insertions, 4 deletions

diff --git a/hobgoblin/src/ast/untyped.hob b/hobgoblin/src/ast/untyped.hob
index 6b74e3e..0fd4403 100644
--- a/hobgoblin/src/ast/untyped.hob
+++ b/hobgoblin/src/ast/untyped.hob
@@ -72,6 +72,8 @@ struct UntypedSumVariantDefinitionNode {
 sum UntypedTypeLevelExpressionNode {
     variant UntypedConstructedTypeNode;
     variant UntypedTypeLevelReferenceNode;
+
+    field source: Source;
 }
 
 struct UntypedConstructedTypeNode {
diff --git a/src/main/java/org/zwobble/hobgoblin/compiler/ast/untyped/UntypedTypeLevelExpressionNode.java b/src/main/java/org/zwobble/hobgoblin/compiler/ast/untyped/UntypedTypeLevelExpressionNode.java
index b5dbd5d..532d8de 100644
--- a/src/main/java/org/zwobble/hobgoblin/compiler/ast/untyped/UntypedTypeLevelExpressionNode.java
+++ b/src/main/java/org/zwobble/hobgoblin/compiler/ast/untyped/UntypedTypeLevelExpressionNode.java
@@ -10,6 +10,8 @@ public sealed interface UntypedTypeLevelExpressionNode permits org.zwobble.hobgo
         // Custom area end: org.zwobble.hobgoblin.compiler.ast.untyped.UntypedTypeLevelExpressionNode.Builder body
     }
 
+    public org.zwobble.hobgoblin.compiler.sources.Source source();
+
     // Custom area start: org.zwobble.hobgoblin.compiler.ast.untyped.UntypedTypeLevelExpressionNode body
     // Custom area end: org.zwobble.hobgoblin.compiler.ast.untyped.UntypedTypeLevelExpressionNode body
 }
diff --git a/src/main/java/org/zwobble/hobgoblin/compiler/typechecker/TypeChecker.java b/src/main/java/org/zwobble/hobgoblin/compiler/typechecker/TypeChecker.java
index 5003e3a..c291aaf 100644
--- a/src/main/java/org/zwobble/hobgoblin/compiler/typechecker/TypeChecker.java
+++ b/src/main/java/org/zwobble/hobgoblin/compiler/typechecker/TypeChecker.java
@@ -258,7 +258,7 @@ public class TypeChecker {
         );
     }
 
-    private static TypedTypeLevelExpressionNode<Type> typeCheckMetaType(
+    static TypedTypeLevelExpressionNode<Type> typeCheckMetaType(
         UntypedTypeLevelExpressionNode untyped,
         TypeCheckerNamespaceContext context
     ) {
@@ -266,8 +266,11 @@ public class TypeChecker {
         if (typed.value() instanceof Type) {
             return (TypedTypeLevelExpressionNode<Type>) typed;
         } else {
-            // TODO: better error
-            throw new RuntimeException("not a metatype");
+            throw new UnexpectedTypeError(
+                new TypeSet.MetaType(),
+                new TypeLevelValueType(typed.value()),
+                untyped.source()
+            );
         }
     }
 
diff --git a/src/test/java/org/zwobble/hobgoblin/compiler/typechecker/TypeCheckerMetaTypeTests.java b/src/test/java/org/zwobble/hobgoblin/compiler/typechecker/TypeCheckerMetaTypeTests.java
new file mode 100644
index 0000000..1f966b1
--- /dev/null
+++ b/src/test/java/org/zwobble/hobgoblin/compiler/typechecker/TypeCheckerMetaTypeTests.java
@@ -0,0 +1,63 @@
+package org.zwobble.hobgoblin.compiler.typechecker;
+
+import org.junit.jupiter.api.Test;
+import org.zwobble.hobgoblin.compiler.ast.typed.TypedTypeLevelReferenceNode;
+import org.zwobble.hobgoblin.compiler.ast.untyped.UntypedArb;
+import org.zwobble.hobgoblin.compiler.types.*;
+
+import java.util.List;
+
+import static org.junit.jupiter.api.Assertions.assertThrows;
+import static org.zwobble.precisely.AssertThat.assertThat;
+import static org.zwobble.precisely.Matchers.*;
+import static org.zwobble.precisely.Matchers.equalTo;
+
+public class TypeCheckerMetaTypeTests {
+    @Test
+    public void whenVariableIsNotTypeLevelValueThenErrorIsThrown() {
+        var untyped = UntypedArb.typeLevelReference("X");
+        var context = TypeCheckerContextArb.namespaceContext();
+        var nativeType = SimpleNativeType.builtin("Int");
+        context.declare("X", nativeType);
+
+        var error = assertThrows(
+            UnexpectedTypeError.class,
+            () -> TypeChecker.typeCheckMetaType(untyped, context)
+        );
+
+        assertThat(error.expected(), equalTo(new TypeSet.MetaType()));
+        assertThat(error.actual(), equalTo(nativeType));
+    }
+
+    @Test
+    public void whenVariableIsTypeLevelValueButNotMetaTypeThenErrorIsThrown() {
+        var untyped = UntypedArb.typeLevelReference("List");
+        var context = TypeCheckerContextArb.namespaceContext();
+        var typeConstructor = new TypeConstructor<>(List.of(new TypeParam("T")), SimpleNativeType.builtin("List"));
+        context.declare("List", new TypeLevelValueType(typeConstructor));
+
+        var error = assertThrows(
+            UnexpectedTypeError.class,
+            () -> TypeChecker.typeCheckMetaType(untyped, context)
+        );
+
+        assertThat(error.expected(), equalTo(new TypeSet.MetaType()));
+        assertThat(error.actual(), equalTo(new TypeLevelValueType(typeConstructor)));
+    }
+
+    @Test
+    public void whenNameIsTypeLevelValueThenValueIsType() {
+        var untyped = UntypedArb.typeLevelReference("X");
+        var context = TypeCheckerContextArb.namespaceContext();
+        var nativeType = SimpleNativeType.builtin("Int");
+        context.declare("X", new TypeLevelValueType(nativeType));
+
+        var typed = TypeChecker.typeCheckMetaType(untyped, context);
+
+        assertThat(typed, instanceOf(
+            TypedTypeLevelReferenceNode.class,
+            has("name", TypedTypeLevelReferenceNode::name, equalTo("X")),
+            has("value", TypedTypeLevelReferenceNode::value, equalTo(nativeType))
+        ));
+    }
+}
diff --git a/src/test/java/org/zwobble/hobgoblin/compiler/typechecker/TypeCheckerTypeLevelReferenceTests.java b/src/test/java/org/zwobble/hobgoblin/compiler/typechecker/TypeCheckerTypeLevelReferenceTests.java
index e633c94..0924eee 100644
--- a/src/test/java/org/zwobble/hobgoblin/compiler/typechecker/TypeCheckerTypeLevelReferenceTests.java
+++ b/src/test/java/org/zwobble/hobgoblin/compiler/typechecker/TypeCheckerTypeLevelReferenceTests.java
@@ -42,7 +42,7 @@ public class TypeCheckerTypeLevelReferenceTests {
     }
 
     @Test
-    public void whenNameIsMetaTypeThenValueIsType() {
+    public void whenNameIsTypeLevelValueThenValueIsType() {
         var untyped = UntypedArb.typeLevelReference("X");
         var context = TypeCheckerContextArb.namespaceContext();
         var nativeType = SimpleNativeType.builtin("Int");