From 9680531a04b43f781afaf15f0fd080569fa73305 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Kev=C4=B1n=20Carpenter=E2=84=A2=EF=B8=8F?=
 <910168+kmccarp@users.noreply.github.com>
Date: Wed, 4 Nov 2026 20:49:54 +0000
Subject: [PATCH] Only add `AddMissingMethodImplementation` templates to Java
 sources

The template printed Java into Kotlin classes, such as 'public <T> unwrap( iface: Class<T>): T {', which does not compile, including where Kotlin delegation already supplies the method.
---
 .../migrate/AddMissingMethodImplementation.java   |  6 +++++-
 .../AddMissingMethodImplementationTest.java       | 15 +++++++++++++++
 2 files changed, 20 insertions(+), 1 deletion(-)

diff --git a/src/main/java/org/openrewrite/java/migrate/AddMissingMethodImplementation.java b/src/main/java/org/openrewrite/java/migrate/AddMissingMethodImplementation.java
index 9152b33e2e..e144d9f684 100644
--- a/src/main/java/org/openrewrite/java/migrate/AddMissingMethodImplementation.java
+++ b/src/main/java/org/openrewrite/java/migrate/AddMissingMethodImplementation.java
@@ -27,6 +27,7 @@
 import org.openrewrite.java.tree.J;
 import org.openrewrite.java.tree.JavaType;
 import org.openrewrite.java.tree.TypeUtils;
+import org.openrewrite.staticanalysis.java.JavaFileChecker;
 
 import java.util.Iterator;
 
@@ -57,7 +58,10 @@ public class AddMissingMethodImplementation extends Recipe {
 
     @Override
     public TreeVisitor<?, ExecutionContext> getVisitor() {
-        return Preconditions.check(new UsesType<>(fullyQualifiedClassName, true), new ClassImplementationVisitor());
+        // The method template is Java, so printing it into a Kotlin or Groovy class would not compile.
+        return Preconditions.check(
+                Preconditions.and(new JavaFileChecker<>(), new UsesType<>(fullyQualifiedClassName, true)),
+                new ClassImplementationVisitor());
     }
 
     public class ClassImplementationVisitor extends JavaIsoVisitor<ExecutionContext> {
diff --git a/src/test/java/org/openrewrite/java/migrate/AddMissingMethodImplementationTest.java b/src/test/java/org/openrewrite/java/migrate/AddMissingMethodImplementationTest.java
index 7d5931efe2..807d30c87b 100644
--- a/src/test/java/org/openrewrite/java/migrate/AddMissingMethodImplementationTest.java
+++ b/src/test/java/org/openrewrite/java/migrate/AddMissingMethodImplementationTest.java
@@ -23,6 +23,7 @@
 
 import static org.openrewrite.java.Assertions.java;
 import static org.openrewrite.java.Assertions.javaVersion;
+import static org.openrewrite.kotlin.Assertions.kotlin;
 
 class AddMissingMethodImplementationTest implements RewriteTest {
 
@@ -234,4 +235,18 @@ class C2 {
           )
         );
     }
+
+    @Test
+    void leaveKotlinAlone() {
+        rewriteRun(
+          spec -> spec.recipe(new AddMissingMethodImplementation("java.lang.Runnable", "java.lang.Runnable run()",
+            "public void run() { }")),
+          //language=kotlin
+          kotlin(
+            """
+              class Delegating(runnable: Runnable) : Runnable by runnable
+              """
+          )
+        );
+    }
 }