From de9e0f9162b625b3008b261967d303da3cc4ae41 Mon Sep 17 00:00:00 2001
From: Michael Williamson <mike@zwobble.org>
Date: Thu, 13 Aug 2026 17:31:50 +0100
Subject: Add wildcard as Java type arg

---
 .../hobgoblin/compiler/output/lang/java/JavaWriter.java  |  5 +++++
 .../compiler/output/lang/java/ast/JavaTypeArg.java       |  7 +++++++
 .../compiler/output/lang/java/JavaWriterTests.java       | 16 ++++++++++++++++
 3 files changed, 28 insertions(+)

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 1d14b29..52c2db1 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
@@ -426,10 +426,15 @@ public class JavaWriter implements AutoCloseable {
             case JavaTypeArg.Invariant invariant -> {
                 writeTypeRef(invariant.type(), writer);
             }
+
             case JavaTypeArg.SuperType superType -> {
                 writer.write("? super ");
                 writeTypeRef(superType.type(), writer);
             }
+
+            case JavaTypeArg.Wildcard wildcard -> {
+                writer.write("?");
+            }
         }
     }
 
diff --git a/src/main/java/org/zwobble/hobgoblin/compiler/output/lang/java/ast/JavaTypeArg.java b/src/main/java/org/zwobble/hobgoblin/compiler/output/lang/java/ast/JavaTypeArg.java
index 8253275..6e520a2 100644
--- a/src/main/java/org/zwobble/hobgoblin/compiler/output/lang/java/ast/JavaTypeArg.java
+++ b/src/main/java/org/zwobble/hobgoblin/compiler/output/lang/java/ast/JavaTypeArg.java
@@ -14,4 +14,11 @@ public sealed interface JavaTypeArg {
 
     record SuperType(JavaTypeRef type) implements JavaTypeArg {
     }
+
+    static JavaTypeArg wildcard() {
+        return new Wildcard();
+    }
+
+    record Wildcard() implements JavaTypeArg {
+    }
 }
diff --git a/src/test/java/org/zwobble/hobgoblin/compiler/output/lang/java/JavaWriterTests.java b/src/test/java/org/zwobble/hobgoblin/compiler/output/lang/java/JavaWriterTests.java
index fb41fa8..de39610 100644
--- a/src/test/java/org/zwobble/hobgoblin/compiler/output/lang/java/JavaWriterTests.java
+++ b/src/test/java/org/zwobble/hobgoblin/compiler/output/lang/java/JavaWriterTests.java
@@ -923,6 +923,22 @@ public class JavaWriterTests {
         assertThat(string, equalTo("abc.def.One<? super Two, ? super Three>"));
     }
 
+    @Test
+    public void typeRefArgCanBeWildcard() throws IOException {
+        var java = JavaTypeRef.topLevelGeneric(
+            JavaPackageName.of("abc", "def"),
+            JavaIdentifier.of("One"),
+            List.of(
+                JavaTypeArg.wildcard(),
+                JavaTypeArg.wildcard()
+            )
+        );
+
+        var string = write(writer -> writer.writeTypeRef(java));
+
+        assertThat(string, equalTo("abc.def.One<?, ?>"));
+    }
+
     @Test
     public void typeRefInnerTypeNameIsSeparatedByDot() throws IOException {
         var java = JavaTypeRef.inner(
-- 
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