From 7eed843944a247a99e48bdb6f9dc3aac17d983c5 Mon Sep 17 00:00:00 2001
From: Michael Williamson <mike@zwobble.org>
Date: Sat, 18 Jul 2026 19:32:20 +0100
Subject: Support options in rust-transient-0

---
 .../rusttransient0/RustTransient0Generator.java    | 74 ++++++++++++++++++++++
 1 file changed, 74 insertions(+)

(limited to 'src/main')

diff --git a/src/main/java/org/zwobble/hobgoblin/compiler/output/generators/rusttransient0/RustTransient0Generator.java b/src/main/java/org/zwobble/hobgoblin/compiler/output/generators/rusttransient0/RustTransient0Generator.java
index a17ae6b..7122e54 100644
--- a/src/main/java/org/zwobble/hobgoblin/compiler/output/generators/rusttransient0/RustTransient0Generator.java
+++ b/src/main/java/org/zwobble/hobgoblin/compiler/output/generators/rusttransient0/RustTransient0Generator.java
@@ -405,6 +405,8 @@ public class RustTransient0Generator implements Generator {
             case ConstructedNativeType constructedNativeType -> {
                 if (constructedNativeType.constructor().equals(NativeTypes.LIST)) {
                     yield generateEncodeList(value, constructedNativeType.args().getFirst());
+                } else if (constructedNativeType.constructor().equals(NativeTypes.OPTION)) {
+                    yield generateEncodeOption(value, constructedNativeType.args().getFirst());
                 } else {
                     yield List.of(new RustExpressionStatement(generateTodo()));
                 }
@@ -441,6 +443,8 @@ public class RustTransient0Generator implements Generator {
             case ConstructedNativeType constructedNativeType -> {
                 if (constructedNativeType.constructor().equals(NativeTypes.LIST)) {
                     yield generateDecodeList(constructedNativeType.args().getFirst());
+                } else if (constructedNativeType.constructor().equals(NativeTypes.OPTION)) {
+                    yield generateDecodeOption(constructedNativeType.args().getFirst());
                 } else {
                     yield generateTodo();
                 }
@@ -560,6 +564,76 @@ public class RustTransient0Generator implements Generator {
         );
     }
 
+    private List<RustStatement> generateEncodeOption(RustExpression value, Type elementType) {
+        return List.of(
+            // TODO: pattern matching
+            new RustExpressionStatement(new RustIfExpression(
+                methodCall(value, RustIdentifier.of("is_some"), List.of()),
+                new RustBlockExpression(
+                    List.of(
+                        new RustExpressionStatement(new RustBlockExpression(
+                            generateEncode(
+                                new RustPrefixExpression(RustPrefixOperator.BORROW, new RustBoolLiteral(true)),
+                                NativeTypes.BOOL
+                            ),
+                            Optional.empty()
+                        )),
+                        new RustExpressionStatement(new RustBlockExpression(
+                            generateEncode(
+                                new RustPrefixExpression(
+                                    RustPrefixOperator.BORROW,
+                                    methodCall(
+                                        methodCall(value, RustIdentifier.of("as_ref"), List.of()),
+                                        RustIdentifier.of("unwrap"),
+                                        List.of()
+                                    )
+                                ),
+                                elementType
+                            ),
+                            Optional.empty()
+                        ))
+                    ),
+                    Optional.empty()
+                ),
+                new RustBlockExpression(
+                    generateEncode(
+                        new RustPrefixExpression(RustPrefixOperator.BORROW, new RustBoolLiteral(false)),
+                        NativeTypes.BOOL
+                    ),
+                    Optional.empty()
+                )
+            ))
+        );
+    }
+
+    private RustExpression generateDecodeOption(Type elementType) {
+        var isSome = RustIdentifier.of("is_some");
+
+        return new RustBlockExpression(
+            List.of(
+                new RustLetStatement(isSome, false, generateDecode(NativeTypes.BOOL))
+            ),
+            Optional.of(new RustIfExpression(
+                RustPath.of(isSome),
+                new RustBlockExpression(
+                    List.of(),
+                    Optional.of(
+                        new RustCallExpression(
+                            RustPath.global("std", "option", "Option", "Some"),
+                            List.of(generateDecode(elementType))
+                        )
+                    )
+                ),
+                new RustBlockExpression(
+                    List.of(),
+                    Optional.of(
+                        RustPath.global("std", "option", "Option", "None")
+                    )
+                )
+            ))
+        );
+    }
+
     private RustExpression generateWriterWrite(RustExpression valueToWrite) {
         return new RustTryPropagationExpression(new RustCallExpression(
             new RustFieldExpression(
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