From 4c2db9bb403c8ffc04eadb6ab262d5137f216000 Mon Sep 17 00:00:00 2001
From: Michael Williamson <mike@zwobble.org>
Date: Sun, 2 Aug 2026 13:54:53 +0100
Subject: Check that sum variant is struct

---
 .../hobgoblin/compiler/typechecker/TypeChecker.java    |  8 ++++++--
 .../errors/SumVariantMustBeStructError.java            | 18 ++++++++++++++++++
 2 files changed, 24 insertions(+), 2 deletions(-)
 create mode 100644 src/main/java/org/zwobble/hobgoblin/compiler/typechecker/errors/SumVariantMustBeStructError.java

(limited to 'src/main/java/org')

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 a40bd92..c2eae29 100644
--- a/src/main/java/org/zwobble/hobgoblin/compiler/typechecker/TypeChecker.java
+++ b/src/main/java/org/zwobble/hobgoblin/compiler/typechecker/TypeChecker.java
@@ -286,8 +286,12 @@ public class TypeChecker {
             } else {
                 variantValueType = variantType.value();
             }
-            // TODO: handle not struct type
-            var variant = new SumVariant(variants.size(), variantType.value(), (StructType) variantValueType);
+
+            if (!(variantValueType instanceof StructType variantValueStructType)) {
+                throw new SumVariantMustBeStructError(variantValueType, untypedVariant.source());
+            }
+
+            var variant = new SumVariant(variants.size(), variantType.value(), variantValueStructType);
             variants.add(variant);
         }
 
diff --git a/src/main/java/org/zwobble/hobgoblin/compiler/typechecker/errors/SumVariantMustBeStructError.java b/src/main/java/org/zwobble/hobgoblin/compiler/typechecker/errors/SumVariantMustBeStructError.java
new file mode 100644
index 0000000..78235ae
--- /dev/null
+++ b/src/main/java/org/zwobble/hobgoblin/compiler/typechecker/errors/SumVariantMustBeStructError.java
@@ -0,0 +1,18 @@
+package org.zwobble.hobgoblin.compiler.typechecker.errors;
+
+import org.zwobble.hobgoblin.compiler.errors.SourceError;
+import org.zwobble.hobgoblin.compiler.sources.Source;
+import org.zwobble.hobgoblin.compiler.types.Type;
+
+public class SumVariantMustBeStructError extends SourceError {
+    private final Type variantType;
+
+    public SumVariantMustBeStructError(Type variantType, Source source) {
+        super("sum variants must be structs, but was " + variantType.describe(), source);
+        this.variantType = variantType;
+    }
+
+    public Type variantType() {
+        return variantType;
+    }
+}
-- 
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