Check shadowing behaviour

1 files changed, 20 insertions, 0 deletions

diff --git a/src/test/java/org/shedlang/compiler/typechecker/TypeCheckerValTests.java b/src/test/java/org/shedlang/compiler/typechecker/TypeCheckerValTests.java
index 1526d3aa..7967e442 100644
--- a/src/test/java/org/shedlang/compiler/typechecker/TypeCheckerValTests.java
+++ b/src/test/java/org/shedlang/compiler/typechecker/TypeCheckerValTests.java
@@ -68,4 +68,24 @@ public class TypeCheckerValTests {
 
         assertThat(error.variableName(), equalTo("x"));
     }
+
+    @Test
+    public void whenValShadowsExistingVariableThenValCannotBeReferencedBeforeDefinition() {
+        var untyped = UntypedFunctionDefinitionNode.builder()
+            .addStatement(Untyped.expressionStatement(Untyped.reference("x")))
+            .addStatement(Untyped.val(Untyped.targetVariable("x"), Untyped.stringLiteral("hello")))
+            .build();
+        var context = TypeCheckerContext.EMPTY
+            .enterBlockWithDefinedVariables(P.map(
+                Map.entry("Unit", Types.metaType(Types.UNIT)),
+                Map.entry("x", Types.INT)
+            ));
+
+        var error = assertThrows(
+            ReferenceBeforeDefinitionError.class,
+            () -> TypeChecker.typeCheckNamespaceStatement(untyped, context)
+        );
+
+        assertThat(error.variableName(), equalTo("x"));
+    }
 }