From 10317b0c2841591a85530a5c4c38cac0c4bf5fe8 Mon Sep 17 00:00:00 2001
From: Michael Williamson <mike@zwobble.org>
Date: Sat, 11 Jul 2026 16:43:48 +0100
Subject: Support enums in Java transient-0

---
 .../java/org/zwobble/example/Transient0Tests.java  | 22 ++++++++++++
 examples/10-transient-0/src/data.hob               |  6 ++++
 .../javatransient0/JavaTransient0Generator.java    | 42 ++++++++++++++++++++--
 3 files changed, 67 insertions(+), 3 deletions(-)

diff --git a/examples/10-transient-0/output/java-junit/src/test/java/org/zwobble/example/Transient0Tests.java b/examples/10-transient-0/output/java-junit/src/test/java/org/zwobble/example/Transient0Tests.java
index cb3ac61..7d6f7de 100644
--- a/examples/10-transient-0/output/java-junit/src/test/java/org/zwobble/example/Transient0Tests.java
+++ b/examples/10-transient-0/output/java-junit/src/test/java/org/zwobble/example/Transient0Tests.java
@@ -9,6 +9,7 @@ import java.util.List;
 import java.util.Optional;
 import org.junit.jupiter.api.Assertions;
 import org.junit.jupiter.api.Test;
+import org.zwobble.example.types.data.EnumWithVariants;
 import org.zwobble.example.types.data.HobgoblinTransient0Data;
 import org.zwobble.example.types.data.InnerStruct;
 import org.zwobble.example.types.data.OuterStruct;
@@ -121,6 +122,27 @@ public class Transient0Tests {
         );
     }
 
+    @Test
+    public void enumWithVariants() throws IOException {
+        assertRoundTripEncoding(
+            EnumWithVariants.ZERO,
+            HobgoblinTransient0Data::encodeEnumWithVariants,
+            HobgoblinTransient0Data::decodeEnumWithVariants
+        );
+
+        assertRoundTripEncoding(
+            EnumWithVariants.ONE,
+            HobgoblinTransient0Data::encodeEnumWithVariants,
+            HobgoblinTransient0Data::decodeEnumWithVariants
+        );
+
+        assertRoundTripEncoding(
+            EnumWithVariants.TWO,
+            HobgoblinTransient0Data::encodeEnumWithVariants,
+            HobgoblinTransient0Data::decodeEnumWithVariants
+        );
+    }
+
     private <T> void assertRoundTripEncoding(
         T value,
         Encoder<T> encoder,
diff --git a/examples/10-transient-0/src/data.hob b/examples/10-transient-0/src/data.hob
index 80ba8e5..f6fa20e 100644
--- a/examples/10-transient-0/src/data.hob
+++ b/examples/10-transient-0/src/data.hob
@@ -37,3 +37,9 @@ struct StructWithOption {
     field a: Option[Int64];
     field b: Option[InnerStruct];
 }
+
+enum EnumWithVariants {
+    variant zero;
+    variant one;
+    variant two;
+}
diff --git a/src/main/java/org/zwobble/hobgoblin/compiler/output/generators/javatransient0/JavaTransient0Generator.java b/src/main/java/org/zwobble/hobgoblin/compiler/output/generators/javatransient0/JavaTransient0Generator.java
index 59dcefe..be04982 100644
--- a/src/main/java/org/zwobble/hobgoblin/compiler/output/generators/javatransient0/JavaTransient0Generator.java
+++ b/src/main/java/org/zwobble/hobgoblin/compiler/output/generators/javatransient0/JavaTransient0Generator.java
@@ -330,7 +330,35 @@ public class JavaTransient0Generator implements Generator {
     ) {
         return switch (statement) {
             case TypedEnumDefinitionNode enumDefinition -> {
-                yield Stream.of();
+                var ordinal = JavaIdentifier.of("ordinal");
+                yield Stream.of(
+                    generateEncodeMethod(
+                        enumDefinition.type(),
+                        new JavaBlock(generateEncode(
+                            new JavaMethodCall(
+                                new JavaRef(VALUE_NAME),
+                                ordinal,
+                                List.of()
+                            ),
+                            NativeTypes.INT_32
+                        ))
+                    ),
+                    generateDecodeMethod(
+                        enumDefinition.type(),
+                        new JavaBlock(Stream.concat(
+                            generateDecode(ordinal, NativeTypes.INT_32).stream(),
+                            Stream.of(new JavaReturn(new JavaArrayAccess(
+                                // TODO: avoid duplicating array each time
+                                new JavaStaticMethodCall(
+                                    this.javaGenerator.generateTypeRef(enumDefinition.type()),
+                                    JavaIdentifier.of("values"),
+                                    List.of()
+                                ),
+                                new JavaRef(ordinal)
+                            )))
+                        ).toList())
+                    )
+                );
             }
 
             case TypedNativeTypeDefinitionNode nativeTypeDefinition -> {
@@ -441,7 +469,11 @@ public class JavaTransient0Generator implements Generator {
             }
 
             case EnumType enumType ->  {
-                throw new UnsupportedOperationException("TODO");
+                yield List.of(generateEncode(
+                    value,
+                    enumType.namespaceName(),
+                    enumType
+                ));
             }
 
             case SimpleNativeType simpleNativeType -> {
@@ -501,7 +533,11 @@ public class JavaTransient0Generator implements Generator {
             }
 
             case EnumType enumType ->  {
-                throw new UnsupportedOperationException("TODO");
+                yield List.of(generateDecode(
+                    target,
+                    enumType.namespaceName(),
+                    enumType
+                ));
             }
 
             case SimpleNativeType simpleNativeType ->  {
-- 
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