Gradle Toolchain support

plugin/src/main/kotlin/org/jlleitschuh/gradle/ktlint/KtlintBasePlugin.kt

@@ -63,6 +63,6 @@ open class KtlintBasePlugin : Plugin<Project> {
     }
 
     companion object {
-        const val LOWEST_SUPPORTED_GRADLE_VERSION = "6.0"
+        const val LOWEST_SUPPORTED_GRADLE_VERSION = "6.7"
     }
 }

plugin/src/main/kotlin/org/jlleitschuh/gradle/ktlint/tasks/BaseKtLintCheckTask.kt

@@ -10,18 +10,24 @@ import org.gradle.api.file.ProjectLayout
 import org.gradle.api.file.RegularFileProperty
 import org.gradle.api.model.ObjectFactory
 import org.gradle.api.model.ReplacedBy
+import org.gradle.api.plugins.JavaBasePlugin
+import org.gradle.api.plugins.JavaPluginExtension
 import org.gradle.api.provider.Property
 import org.gradle.api.provider.SetProperty
 import org.gradle.api.tasks.Classpath
 import org.gradle.api.tasks.Input
 import org.gradle.api.tasks.InputFile
 import org.gradle.api.tasks.InputFiles
 import org.gradle.api.tasks.Internal
+import org.gradle.api.tasks.Nested
+import org.gradle.api.tasks.Optional
 import org.gradle.api.tasks.OutputFile
 import org.gradle.api.tasks.PathSensitive
 import org.gradle.api.tasks.PathSensitivity
 import org.gradle.api.tasks.SkipWhenEmpty
 import org.gradle.api.tasks.SourceTask
+import org.gradle.jvm.toolchain.JavaLauncher
+import org.gradle.jvm.toolchain.JavaToolchainService
 import org.gradle.work.ChangeType
 import org.gradle.work.Incremental
 import org.gradle.work.InputChanges
@@ -43,6 +49,10 @@ abstract class BaseKtLintCheckTask @Inject constructor(
     private val workerExecutor: WorkerExecutor,
 ) : SourceTask() {
 
+    @get:Nested
+    @get:Optional
+    abstract val launcher: Property<JavaLauncher>
+
     @get:Classpath
     internal abstract val ktLintClasspath: ConfigurableFileCollection
 
@@ -95,6 +105,14 @@ abstract class BaseKtLintCheckTask @Inject constructor(
                 include("**/*.$it")
             }
         }
+
+        project.plugins.withType(JavaBasePlugin::class.java).configureEach {
+            val toolchain = project.extensions.getByType(JavaPluginExtension::class.java).toolchain
+
+            val service = project.extensions.getByType(JavaToolchainService::class.java)
+            val defaultLauncher = service.launcherFor(toolchain)
+            launcher.convention(defaultLauncher)
+        }
     }
 
     @ReplacedBy("stableSources")
@@ -150,6 +168,9 @@ abstract class BaseKtLintCheckTask @Inject constructor(
             spec.classpath.from(ktLintClasspath, ruleSetsClasspath)
             spec.forkOptions { options ->
                 options.maxHeapSize = workerMaxHeapSize.get()
+                if(launcher.isPresent) {
+                    options.executable = launcher.get().executablePath.asFile.absolutePath
+                }
             }
         }
 

plugin/src/test/kotlin/org/jlleitschuh/gradle/ktlint/KtlintPluginTest.kt

@@ -480,4 +480,40 @@ abstract class BaseKtlintPluginTest : AbstractPluginTest() {
             assertThat(output).contains("com.pinterest.ktlint:ktlint-core:0.34.2 -> 0.41.0")
         }
     }
+
+    @Test
+    internal fun `Should use JVM Toolchains`() {
+        val initialSourceFile = "src/main/kotlin/initial.kt"
+        projectRoot.createSourceFile(
+            initialSourceFile,
+            """
+            val foo = "bar"
+
+            """.trimIndent()
+        )
+
+
+        projectRoot.buildFile().appendText(
+            """
+
+            java {
+                toolchain {
+                    languageVersion.set(JavaLanguageVersion.of(16))
+                }
+            }
+
+            tasks.withType(org.jlleitschuh.gradle.ktlint.tasks.KtLintCheckTask) {
+                doLast {
+                    project.logger.lifecycle("Running ktlint task with JDK ${'$'}{it.launcher.get().metadata.languageVersion.asInt()}")
+                }
+            }
+            """.trimIndent()
+        )
+
+        build(CHECK_PARENT_TASK_NAME).apply {
+            assertThat(task(":$mainSourceSetCheckTaskName")?.outcome).isEqualTo(TaskOutcome.SUCCESS)
+            assertThat(output.contains("Running ktlint task with JDK 16"))
+        }
+
+    }
 }