Don't use Gradle toolchains to specify Java version

build-logic/build.gradle.kts

@@ -52,6 +52,10 @@ gradlePlugin {
             id = "mavenPlugin"
             implementationClass = "org.teavm.buildutil.MavenPluginPlugin"
         }
+        create("javaVersion") {
+            id = "javaVersion"
+            implementationClass = "org.teavm.buildutil.JavaVersionPlugin"
+        }
     }
 }
 
@@ -61,9 +65,7 @@ checkstyle {
 }
 
 java {
-    toolchain {
-        languageVersion.set(JavaLanguageVersion.of(11))
-    }
+    sourceCompatibility = JavaVersion.VERSION_11
 }
 
 val generatedConfigDir = project.layout.buildDirectory.dir("generated/config").get()

build-logic/src/main/java/org/teavm/buildutil/JavaVersionExtension.java

@@ -0,0 +1,24 @@
+/*
+ *  Copyright 2023 Alexey Andreev.
+ *
+ *  Licensed under the Apache License, Version 2.0 (the "License");
+ *  you may not use this file except in compliance with the License.
+ *  You may obtain a copy of the License at
+ *
+ *       http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *  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.teavm.buildutil;
+
+import org.gradle.api.JavaVersion;
+
+public interface JavaVersionExtension {
+    JavaVersion getVersion();
+
+    void setVersion(JavaVersion version);
+}

build-logic/src/main/java/org/teavm/buildutil/JavaVersionPlugin.java

@@ -0,0 +1,52 @@
+/*
+ *  Copyright 2023 Alexey Andreev.
+ *
+ *  Licensed under the Apache License, Version 2.0 (the "License");
+ *  you may not use this file except in compliance with the License.
+ *  You may obtain a copy of the License at
+ *
+ *       http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *  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.teavm.buildutil;
+
+import org.gradle.api.JavaVersion;
+import org.gradle.api.Plugin;
+import org.gradle.api.Project;
+import org.gradle.api.plugins.JavaPluginExtension;
+
+public class JavaVersionPlugin implements Plugin<Project> {
+    @Override
+    public void apply(Project project) {
+        var ext = new ExtensionImpl();
+        project.getExtensions().add(JavaVersionExtension.class, "javaVersion", ext);
+        project.afterEvaluate(p -> {
+            var java = p.getExtensions().findByType(JavaPluginExtension.class);
+            if (java != null) {
+                if (ext.version != null) {
+                    java.setSourceCompatibility(ext.version);
+                    java.setTargetCompatibility(ext.version);
+                }
+            }
+        });
+    }
+
+    private static class ExtensionImpl implements JavaVersionExtension {
+        private JavaVersion version = JavaVersion.VERSION_11;
+
+        @Override
+        public JavaVersion getVersion() {
+            return version;
+        }
+
+        @Override
+        public void setVersion(JavaVersion version) {
+            this.version = version;
+        }
+    }
+}

samples/settings.gradle.kts

@@ -84,10 +84,7 @@ gradle.afterProject {
                     .findVersion("checkstyle").get().requiredVersion
             configDirectory.set(File(settings.rootDir, "../config/checkstyle"))
         }
-        java.toolchain {
-            if (!languageVersion.isPresent) {
-                languageVersion.set(JavaLanguageVersion.of(11))
-            }
-        }
+        java.sourceCompatibility = JavaVersion.VERSION_11
+        java.targetCompatibility = JavaVersion.VERSION_11
     }
 }

settings.gradle.kts

@@ -59,6 +59,10 @@ gradle.allprojects {
     version = teavmVersion
 }
 
+gradle.allprojects {
+    apply(plugin = "javaVersion")
+}
+
 gradle.afterProject {
     val java = extensions.findByType<JavaPluginExtension>()
     if (java != null) {
@@ -67,11 +71,6 @@ gradle.afterProject {
             toolVersion = extensions.getByType<VersionCatalogsExtension>().named("libs")
                     .findVersion("checkstyle").get().requiredVersion
         }
-        java.toolchain {
-            if (!languageVersion.isPresent) {
-                languageVersion.set(JavaLanguageVersion.of(11))
-            }
-        }
     }
 
     extensions.findByType<PublishingExtension>()?.apply {

tests/build.gradle.kts

@@ -20,10 +20,8 @@ plugins {
 
 description = "Tests"
 
-java {
-    toolchain {
-        languageVersion.set(JavaLanguageVersion.of(17))
-    }
+javaVersion {
+    version = JavaVersion.VERSION_17
 }
 
 dependencies {