Fix native image compilation when Logback is not on the classpath (#491)

* Fix native image compilation when Logback is not on the classpath

Fixes #465


---------

Co-authored-by: Lars Bilger <lars.bilger@lht.dlh.de>

Author: lbilger

build.gradle.kts

@@ -144,6 +144,7 @@ kotlin {
                 compileOnly("org.slf4j:slf4j-api:${extra["slf4j_version"]}")
                 compileOnly("ch.qos.logback:logback-classic:${extra["logback_version"]}")
                 compileOnly("org.jetbrains.kotlinx:kotlinx-coroutines-slf4j:${extra["coroutines_version"]}")
+                compileOnly("org.graalvm.sdk:nativeimage:${extra["nativeimage_version"]}")
             }
         }
         val jvmLogbackTest by getting {

src/jvmMain/kotlin/io/github/oshai/kotlinlogging/internal/KLoggerFactory.kt

@@ -10,6 +10,8 @@ internal actual object KLoggerFactory {
 
   /** get logger by explicit name */
   internal actual fun logger(name: String): KLogger {
+    // Note: any changes here might have to be also applied to
+    // [Target_io_github_oshai_kotlinlogging_internal_KLoggerFactory].
     if (System.getProperty("kotlin-logging-to-jul") != null) {
       return JulLoggerFactory.wrapJLogger(JulLoggerFactory.jLogger(name))
     } else if (System.getProperty("kotlin-logging-to-logback") == "true") {

src/jvmMain/kotlin/io/github/oshai/kotlinlogging/internal/Target_io_github_oshai_kotlinlogging_internal_KLoggerFactory.kt

@@ -0,0 +1,47 @@
+package io.github.oshai.kotlinlogging.internal
+
+import com.oracle.svm.core.annotate.Substitute
+import com.oracle.svm.core.annotate.TargetClass
+import com.oracle.svm.core.annotate.TargetElement
+import io.github.oshai.kotlinlogging.KLogger
+import io.github.oshai.kotlinlogging.jul.internal.JulLoggerFactory
+import io.github.oshai.kotlinlogging.slf4j.internal.Slf4jLoggerFactory
+import java.util.function.BooleanSupplier
+
+/**
+ * This class is a substitution class as described in
+ * [https://build-native-java-apps.cc/developer-guide/substitution/]. It fixes an issue where the
+ * native build (GraalVM native-image) fails if Logback is not on the classpath. See
+ * [https://github.com/oshai/kotlin-logging/issues/465]. The weird-looking class name is according
+ * to convention.
+ */
+@Suppress("unused")
+internal class Target_io_github_oshai_kotlinlogging_internal_KLoggerFactory {
+  @TargetClass(
+    className = "io.github.oshai.kotlinlogging.internal.KLoggerFactory",
+    onlyWith = [LogbackNotOnClasspath::class],
+  )
+  companion object {
+    @Substitute
+    @TargetElement(name = "logger\$kotlin_logging")
+    fun logger(name: String): KLogger {
+      if (System.getProperty("kotlin-logging-to-jul") != null) {
+        return JulLoggerFactory.wrapJLogger(JulLoggerFactory.jLogger(name))
+      }
+      // Intentionally leave out the logback branch as logback is not on the classpath.
+      // default to SLF4J
+      return Slf4jLoggerFactory.wrapJLogger(Slf4jLoggerFactory.jLogger(name))
+    }
+  }
+}
+
+internal class LogbackNotOnClasspath : BooleanSupplier {
+  override fun getAsBoolean(): Boolean {
+    try {
+      Class.forName("ch.qos.logback.classic.LoggerContext")
+      return false
+    } catch (_: ClassNotFoundException) {
+      return true
+    }
+  }
+}

versions.gradle.kts

@@ -6,3 +6,4 @@ extra["junit_version"] = "5.9.2"
 extra["logback_version"] = "1.5.11"
 extra["logstash_logback_encoder_version"] = "8.0"
 extra["jackson_version"] = "2.18.3"
+extra["nativeimage_version"] = "24.2.0"