Check type of receiver in field access

2 files changed, 30 insertions, 1 deletions

diff --git a/src/main/java/org/shedlang/compiler/typechecker/TypeChecker.java b/src/main/java/org/shedlang/compiler/typechecker/TypeChecker.java
index f11b0e1e..37cd45ac 100644
--- a/src/main/java/org/shedlang/compiler/typechecker/TypeChecker.java
+++ b/src/main/java/org/shedlang/compiler/typechecker/TypeChecker.java
@@ -5,6 +5,7 @@ import org.shedlang.compiler.ast.typed.*;
 import org.shedlang.compiler.ast.untyped.*;
 import org.shedlang.compiler.sources.Source;
 import org.shedlang.compiler.typechecker.errors.*;
+import org.shedlang.compiler.typechecker.errors.NoSuchFieldError;
 import org.shedlang.compiler.typechecker.typesets.TypeSetTypeLevelValue;
 import org.shedlang.compiler.typechecker.typesets.TypeSets;
 import org.shedlang.compiler.types.*;
@@ -401,8 +402,12 @@ public class TypeChecker {
         var typedReceiver = typedReceiverResult.value();
         context = typedReceiverResult.context();
 
+        if (!(typedReceiver.type() instanceof StructType receiverType)) {
+            throw new NoSuchFieldError(typedReceiver.type(), untyped.fieldName(), untyped.source());
+        }
+
         var structTypeInfo = context.structTypeInfo(
-            (StructType) typedReceiver.type(),
+            receiverType,
             untyped.fieldName()
         );
 
diff --git a/src/main/java/org/shedlang/compiler/typechecker/errors/NoSuchFieldError.java b/src/main/java/org/shedlang/compiler/typechecker/errors/NoSuchFieldError.java
new file mode 100644
index 00000000..91e067ac
--- /dev/null
+++ b/src/main/java/org/shedlang/compiler/typechecker/errors/NoSuchFieldError.java
@@ -0,0 +1,24 @@
+package org.shedlang.compiler.typechecker.errors;
+
+import org.shedlang.compiler.errors.SourceError;
+import org.shedlang.compiler.sources.Source;
+import org.shedlang.compiler.types.Type;
+
+public class NoSuchFieldError extends SourceError {
+    private final Type type;
+    private final String fieldName;
+
+    public NoSuchFieldError(Type type, String fieldName, Source source) {
+        super("No field named " + fieldName + " on type " + type, source);
+        this.type = type;
+        this.fieldName = fieldName;
+    }
+
+    public Type type() {
+        return type;
+    }
+
+    public String fieldName() {
+        return fieldName;
+    }
+}