Align Kotlin jvmTarget with the Java version during UpgradeJavaVersion

build.gradle.kts

@@ -56,6 +56,7 @@ dependencies {
 
     implementation(platform("org.openrewrite:rewrite-bom:${rewriteVersion}"))
     implementation("org.openrewrite:rewrite-java")
+    implementation("org.openrewrite:rewrite-kotlin")
     implementation("org.openrewrite:rewrite-properties")
     implementation("org.openrewrite:rewrite-xml")
     implementation("org.openrewrite:rewrite-json")
@@ -80,7 +81,6 @@ dependencies {
     testImplementation("org.junit-pioneer:junit-pioneer:2.0.0")
 
     testImplementation("org.openrewrite:rewrite-test")
-    testImplementation("org.openrewrite:rewrite-kotlin")
     testImplementation("org.openrewrite.gradle.tooling:model:$rewriteVersion")
 
     testImplementation("org.assertj:assertj-core:latest.release")

src/main/java/org/openrewrite/java/migrate/UpgradeJavaVersion.java

@@ -55,7 +55,8 @@ public List<Recipe> getRecipeList() {
                 new org.openrewrite.jenkins.UpgradeJavaVersion(version, null),
                 new UpdateJavaCompatibility(version, null, null, false, null),
                 new UpdateSdkMan(String.valueOf(version), null),
-                new UpgradeDockerImageVersion(version)
+                new UpgradeDockerImageVersion(version),
+                new UpgradeKotlinJvmTargetVersion(version)
         );
     }
 

src/main/java/org/openrewrite/java/migrate/UpgradeKotlinJvmTargetVersion.java

@@ -0,0 +1,295 @@
+/*
+ * Copyright 2026 the original author or authors.
+ * <p>
+ * Licensed under the Moderne Source Available License (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ * <p>
+ * https://docs.moderne.io/licensing/moderne-source-available-license
+ * <p>
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.openrewrite.java.migrate;
+
+import lombok.EqualsAndHashCode;
+import lombok.Value;
+import org.jspecify.annotations.Nullable;
+import org.openrewrite.Cursor;
+import org.openrewrite.ExecutionContext;
+import org.openrewrite.Option;
+import org.openrewrite.Recipe;
+import org.openrewrite.SourceFile;
+import org.openrewrite.Tree;
+import org.openrewrite.TreeVisitor;
+import org.openrewrite.groovy.GroovyIsoVisitor;
+import org.openrewrite.java.MethodMatcher;
+import org.openrewrite.java.tree.Expression;
+import org.openrewrite.java.tree.J;
+import org.openrewrite.kotlin.KotlinIsoVisitor;
+import org.openrewrite.maven.MavenIsoVisitor;
+import org.openrewrite.xml.ChangeTagValueVisitor;
+import org.openrewrite.xml.tree.Xml;
+
+import java.util.Collections;
+import java.util.Iterator;
+
+@EqualsAndHashCode(callSuper = false)
+@Value
+public class UpgradeKotlinJvmTargetVersion extends Recipe {
+
+    // Gradle build scripts usually lack type attribution, so match by name + arity (matchUnknownTypes=true at call sites).
+    private static final MethodMatcher KOTLIN_OPTIONS = new MethodMatcher("* kotlinOptions(..)");
+    private static final MethodMatcher COMPILER_OPTIONS = new MethodMatcher("* compilerOptions(..)");
+    private static final MethodMatcher JVM_TARGET_SET = new MethodMatcher("* set(..)");
+
+    @Option(displayName = "Java version",
+            description = "The Java version to align Kotlin's `jvmTarget` with.",
+            example = "21")
+    Integer version;
+
+    String displayName = "Upgrade Kotlin `jvmTarget` to match the Java version";
+
+    String description = "Align the Kotlin `jvmTarget` with the project's Java version so the Kotlin compiler emits " +
+            "bytecode at the same level as `javac`. Covers `kotlin-maven-plugin` `<jvmTarget>` configuration and the " +
+            "Gradle `kotlinOptions { jvmTarget = ... }` / `compilerOptions { jvmTarget = ... }` blocks (Groovy and " +
+            "Kotlin DSL). Will not downgrade if the existing Kotlin target is higher than the requested version.";
+
+    @Override
+    public TreeVisitor<?, ExecutionContext> getVisitor() {
+        String newVersion = version.toString();
+        int target = version;
+        // Each language visitor already accepts only its own source kind (the Maven visitor even narrows to actual
+        // Maven poms), so route on `isAcceptable` rather than re-checking compilation-unit types here.
+        TreeVisitor<?, ExecutionContext> maven = mavenVisitor(target);
+        TreeVisitor<?, ExecutionContext> groovy = gradleGroovyVisitor(newVersion, target);
+        TreeVisitor<?, ExecutionContext> kotlin = gradleKotlinDslVisitor(newVersion, target);
+        return new TreeVisitor<Tree, ExecutionContext>() {
+            @Override
+            public @Nullable Tree visit(@Nullable Tree tree, ExecutionContext ctx) {
+                if (tree instanceof SourceFile) {
+                    SourceFile sourceFile = (SourceFile) tree;
+                    if (maven.isAcceptable(sourceFile, ctx)) {
+                        return maven.visit(tree, ctx);
+                    }
+                    if (groovy.isAcceptable(sourceFile, ctx)) {
+                        return groovy.visit(tree, ctx);
+                    }
+                    if (kotlin.isAcceptable(sourceFile, ctx)) {
+                        return kotlin.visit(tree, ctx);
+                    }
+                }
+                return tree;
+            }
+        };
+    }
+
+    private static MavenIsoVisitor<ExecutionContext> mavenVisitor(int target) {
+        return new MavenIsoVisitor<ExecutionContext>() {
+            @Override
+            public Xml.Tag visitTag(Xml.Tag tag, ExecutionContext ctx) {
+                Xml.Tag t = super.visitTag(tag, ctx);
+                if (!isPluginTag("org.jetbrains.kotlin", "kotlin-maven-plugin")) {
+                    return t;
+                }
+                Xml.Tag jvmTarget = t.getChild("configuration")
+                        .flatMap(config -> config.getChild("jvmTarget"))
+                        .orElse(null);
+                if (jvmTarget == null) {
+                    return t;
+                }
+                Integer current = parseJvmTarget(jvmTarget.getValue().orElse(null));
+                if (current == null || current >= target) {
+                    return t;
+                }
+                return (Xml.Tag) new ChangeTagValueVisitor<>(jvmTarget, Integer.toString(target)).visitNonNull(t, ctx);
+            }
+        };
+    }
+
+    private static GroovyIsoVisitor<ExecutionContext> gradleGroovyVisitor(String newVersion, int target) {
+        return new GroovyIsoVisitor<ExecutionContext>() {
+            @Override
+            public J.Assignment visitAssignment(J.Assignment assignment, ExecutionContext ctx) {
+                J.Assignment a = super.visitAssignment(assignment, ctx);
+                // A string `jvmTarget` is only valid in the legacy `kotlinOptions` block; bumping one inside
+                // `compilerOptions` would leave a non-compiling String assignment to a `Property<JvmTarget>`.
+                if (!"kotlinOptions".equals(enclosingKotlinCompilerBlock(getCursor()))) {
+                    return a;
+                }
+                Expression variable = a.getVariable();
+                if (!(variable instanceof J.Identifier)
+                        || !"jvmTarget".equals(((J.Identifier) variable).getSimpleName())) {
+                    return a;
+                }
+                Expression rhs = a.getAssignment();
+                if (!(rhs instanceof J.Literal)) {
+                    return a;
+                }
+                J.Literal literal = (J.Literal) rhs;
+                Object value = literal.getValue();
+                if (!(value instanceof String)) {
+                    return a;
+                }
+                Integer current = parseJvmTarget((String) value);
+                if (current == null || current >= target) {
+                    return a;
+                }
+                // Preserve the original quote style (Groovy allows both ' and ").
+                String original = literal.getValueSource();
+                char quote = original != null && !original.isEmpty() ? original.charAt(0) : '\'';
+                return a.withAssignment(literal
+                        .withValue(newVersion)
+                        .withValueSource(quote + newVersion + quote));
+            }
+        };
+    }
+
+    private static KotlinIsoVisitor<ExecutionContext> gradleKotlinDslVisitor(String newVersion, int target) {
+        return new KotlinIsoVisitor<ExecutionContext>() {
+            @Override
+            public J.Assignment visitAssignment(J.Assignment assignment, ExecutionContext ctx) {
+                J.Assignment a = super.visitAssignment(assignment, ctx);
+                if (!isInsideKotlinCompilerBlock(getCursor())) {
+                    return a;
+                }
+                Expression variable = a.getVariable();
+                if (!(variable instanceof J.Identifier)
+                        || !"jvmTarget".equals(((J.Identifier) variable).getSimpleName())) {
+                    return a;
+                }
+                Expression rhs = a.getAssignment();
+                if (rhs instanceof J.Literal) {
+                    // A string-literal `jvmTarget` is only valid in the legacy `kotlinOptions` block. Inside
+                    // `compilerOptions` it is `Property<JvmTarget>` and a String assignment does not compile, so
+                    // leave such (already-invalid) input untouched — `UseJvmTargetProviderSyntax` converts it.
+                    if ("kotlinOptions".equals(enclosingKotlinCompilerBlock(getCursor()))) {
+                        return bumpLiteralAssignment(a, (J.Literal) rhs, newVersion, target);
+                    }
+                    return a;
+                }
+                if (rhs instanceof J.FieldAccess) {
+                    J.FieldAccess fa = (J.FieldAccess) rhs;
+                    J.FieldAccess bumped = bumpedJvmTargetFieldAccess(fa, newVersion, target);
+                    return bumped == fa ? a : a.withAssignment(bumped);
+                }
+                return a;
+            }
+
+            @Override
+            public J.MethodInvocation visitMethodInvocation(J.MethodInvocation method, ExecutionContext ctx) {
+                J.MethodInvocation mi = super.visitMethodInvocation(method, ctx);
+                // Match the Provider-style setter `jvmTarget.set(JvmTarget.JVM_X)`.
+                if (!JVM_TARGET_SET.matches(mi, true) || !(mi.getSelect() instanceof J.Identifier)) {
+                    return mi;
+                }
+                if (!"jvmTarget".equals(((J.Identifier) mi.getSelect()).getSimpleName())) {
+                    return mi;
+                }
+                if (!isInsideKotlinCompilerBlock(getCursor())) {
+                    return mi;
+                }
+                if (mi.getArguments().size() != 1) {
+                    return mi;
+                }
+                Expression arg = mi.getArguments().get(0);
+                if (arg instanceof J.FieldAccess) {
+                    J.FieldAccess fa = (J.FieldAccess) arg;
+                    J.FieldAccess bumped = bumpedJvmTargetFieldAccess(fa, newVersion, target);
+                    if (bumped != fa) {
+                        return mi.withArguments(Collections.singletonList(bumped));
+                    }
+                }
+                return mi;
+            }
+        };
+    }
+
+    private static boolean isInsideKotlinCompilerBlock(Cursor cursor) {
+        return enclosingKotlinCompilerBlock(cursor) != null;
+    }
+
+    /**
+     * The simple name of the nearest enclosing Kotlin compile-config DSL block (`kotlinOptions` or
+     * `compilerOptions`), or {@code null} if there is none. Gradle build scripts lack type attribution, so the
+     * enclosing block is matched by name (matchUnknownTypes=true), the same approach
+     * `org.openrewrite.gradle.UpdateJavaCompatibility` uses for `java { }` / `sourceCompatibility`.
+     * <p>
+     * The distinction matters: `jvmTarget` is a `String` in the legacy `kotlinOptions` DSL but a
+     * `Property<JvmTarget>` in `compilerOptions`, so a string-literal value is only valid under `kotlinOptions`.
+     */
+    private static @Nullable String enclosingKotlinCompilerBlock(Cursor cursor) {
+        Iterator<Object> path = cursor.getPath();
+        while (path.hasNext()) {
+            Object o = path.next();
+            if (o instanceof J.MethodInvocation) {
+                J.MethodInvocation mi = (J.MethodInvocation) o;
+                if (KOTLIN_OPTIONS.matches(mi, true)) {
+                    return "kotlinOptions";
+                }
+                if (COMPILER_OPTIONS.matches(mi, true)) {
+                    return "compilerOptions";
+                }
+            }
+        }
+        return null;
+    }
+
+    private static J.Assignment bumpLiteralAssignment(J.Assignment a, J.Literal literal, String newVersion, int target) {
+        Object value = literal.getValue();
+        if (!(value instanceof String)) {
+            return a;
+        }
+        Integer current = parseJvmTarget((String) value);
+        if (current == null || current >= target) {
+            return a;
+        }
+        return a.withAssignment(literal
+                .withValue(newVersion)
+                .withValueSource("\"" + newVersion + "\""));
+    }
+
+    /**
+     * If the FieldAccess is a {@code JvmTarget.JVM_X} reference with X less than {@code target},
+     * return a new FieldAccess with the bumped enum name. Returns the original instance unchanged otherwise.
+     */
+    private static J.FieldAccess bumpedJvmTargetFieldAccess(J.FieldAccess fa, String newVersion, int target) {
+        if (!(fa.getTarget() instanceof J.Identifier)
+                || !"JvmTarget".equals(((J.Identifier) fa.getTarget()).getSimpleName())) {
+            return fa;
+        }
+        String enumName = fa.getSimpleName();
+        if (!enumName.startsWith("JVM_")) {
+            return fa;
+        }
+        // Enum constants spell the version with underscores ("JVM_1_8", "JVM_11"); normalize to the dotted/plain
+        // form parseJvmTarget understands ("1.8", "11").
+        Integer current = parseJvmTarget(enumName.substring("JVM_".length()).replace('_', '.'));
+        if (current == null || current >= target) {
+            return fa;
+        }
+        return fa.withName(fa.getName().withSimpleName("JVM_" + newVersion));
+    }
+
+    /**
+     * Parse a Kotlin {@code jvmTarget} string ("1.8", "11", "21") to the corresponding major Java version.
+     * Returns {@code null} if the value cannot be parsed (do-no-harm).
+     */
+    private static @Nullable Integer parseJvmTarget(@Nullable String raw) {
+        if (raw == null) {
+            return null;
+        }
+        String trimmed = raw.trim();
+        if ("1.8".equals(trimmed)) {
+            return 8;
+        }
+        try {
+            return Integer.parseInt(trimmed);
+        } catch (NumberFormatException e) {
+            return null;
+        }
+    }
+}