From 612ac53d6d58d0317ab5cec4f3568839ffccdc1b Mon Sep 17 00:00:00 2001
From: Michael Williamson <mike@zwobble.org>
Date: Mon, 18 May 2026 18:45:49 +0100
Subject: Add empty Builder to structs

---
 .../generators/javatypes/JavaTypesGenerator.java   | 25 ++++++++++++++++------
 .../compiler/output/lang/java/JavaWriter.java      |  4 ++++
 .../lang/java/ast/JavaClassBodyDeclaration.java    |  2 +-
 .../output/lang/java/ast/JavaTypeDeclaration.java  |  2 +-
 4 files changed, 24 insertions(+), 9 deletions(-)

diff --git a/src/main/java/org/zwobble/hobgoblin/compiler/output/generators/javatypes/JavaTypesGenerator.java b/src/main/java/org/zwobble/hobgoblin/compiler/output/generators/javatypes/JavaTypesGenerator.java
index 1259552..c4bdccc 100644
--- a/src/main/java/org/zwobble/hobgoblin/compiler/output/generators/javatypes/JavaTypesGenerator.java
+++ b/src/main/java/org/zwobble/hobgoblin/compiler/output/generators/javatypes/JavaTypesGenerator.java
@@ -1,5 +1,6 @@
 package org.zwobble.hobgoblin.compiler.output.generators.javatypes;
 
+import org.zwobble.hobgoblin.compiler.ast.DocComment;
 import org.zwobble.hobgoblin.compiler.ast.typed.TypedNamespaceNode;
 import org.zwobble.hobgoblin.compiler.ast.typed.TypedStructDefinitionNode;
 import org.zwobble.hobgoblin.compiler.ast.typed.TypedSumDefinitionNode;
@@ -116,16 +117,26 @@ public class JavaTypesGenerator implements Generator {
         TypedStructDefinitionNode structDefinition,
         HashMap<String, List<JavaTypeRef>> javaClassToImplementsType
     ) {
+        var components = structDefinition.fields().stream()
+            .map(field -> new JavaRecordComponent(
+                generateTypeRef(field.type()),
+                field.name()
+            ))
+            .toList();
+
         return new JavaRecordDeclaration(
             structDefinition.name(),
-            structDefinition.fields().stream()
-                .map(field -> new JavaRecordComponent(
-                    generateTypeRef(field.type()),
-                    field.name()
-                ))
-                .toList(),
+            components,
             javaClassToImplementsType.getOrDefault(structDefinition.name(), List.of()),
-            List.of(),
+            List.of(
+                new JavaRecordDeclaration(
+                    "Builder",
+                    components,
+                    List.of(),
+                    List.of(),
+                    DocComment.EMPTY
+                )
+            ),
             structDefinition.docComment()
         );
     }
diff --git a/src/main/java/org/zwobble/hobgoblin/compiler/output/lang/java/JavaWriter.java b/src/main/java/org/zwobble/hobgoblin/compiler/output/lang/java/JavaWriter.java
index 2b2cb58..0d25a0e 100644
--- a/src/main/java/org/zwobble/hobgoblin/compiler/output/lang/java/JavaWriter.java
+++ b/src/main/java/org/zwobble/hobgoblin/compiler/output/lang/java/JavaWriter.java
@@ -96,6 +96,10 @@ public class JavaWriter implements AutoCloseable {
             case JavaMethodDeclaration methodDeclaration -> {
                 writeMethodDeclaration(methodDeclaration);
             }
+
+            case JavaTypeDeclaration typeDeclaration -> {
+                writeTypeDeclaration(typeDeclaration);
+            }
         }
     }
 
diff --git a/src/main/java/org/zwobble/hobgoblin/compiler/output/lang/java/ast/JavaClassBodyDeclaration.java b/src/main/java/org/zwobble/hobgoblin/compiler/output/lang/java/ast/JavaClassBodyDeclaration.java
index eb7a0e4..ee2a3a7 100644
--- a/src/main/java/org/zwobble/hobgoblin/compiler/output/lang/java/ast/JavaClassBodyDeclaration.java
+++ b/src/main/java/org/zwobble/hobgoblin/compiler/output/lang/java/ast/JavaClassBodyDeclaration.java
@@ -1,4 +1,4 @@
 package org.zwobble.hobgoblin.compiler.output.lang.java.ast;
 
-public sealed interface JavaClassBodyDeclaration permits JavaMethodDeclaration {
+public sealed interface JavaClassBodyDeclaration permits JavaMethodDeclaration, JavaTypeDeclaration {
 }
diff --git a/src/main/java/org/zwobble/hobgoblin/compiler/output/lang/java/ast/JavaTypeDeclaration.java b/src/main/java/org/zwobble/hobgoblin/compiler/output/lang/java/ast/JavaTypeDeclaration.java
index da6481e..2ad8967 100644
--- a/src/main/java/org/zwobble/hobgoblin/compiler/output/lang/java/ast/JavaTypeDeclaration.java
+++ b/src/main/java/org/zwobble/hobgoblin/compiler/output/lang/java/ast/JavaTypeDeclaration.java
@@ -1,5 +1,5 @@
 package org.zwobble.hobgoblin.compiler.output.lang.java.ast;
 
-public sealed interface JavaTypeDeclaration permits JavaClassDeclaration, JavaInterfaceDeclaration, JavaRecordDeclaration {
+public sealed interface JavaTypeDeclaration extends JavaClassBodyDeclaration permits JavaClassDeclaration, JavaInterfaceDeclaration, JavaRecordDeclaration {
     String name();
 }
-- 
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