Leverage tail recursion when creating message out of Throwable

src/directMain/kotlin/io/github/oshai/kotlinlogging/Formatter.kt

@@ -29,16 +29,13 @@ public class DefaultMessageFormatter(private val includePrefix: Boolean = true)
     }
   }
 
-  private fun Throwable?.throwableToString(): String {
-    if (this == null) {
-      return ""
-    }
-    var msg = ""
-    var current = this
-    while (current != null && current.cause != current) {
-      msg += ", Caused by: '${current.message}'"
-      current = current.cause
+  private fun Throwable?.throwableToString() = createThrowableMsg("", this)
+
+  private tailrec fun createThrowableMsg(msg: String, throwable: Throwable?): String {
+    return if (throwable == null || throwable.cause == throwable) {
+      msg
+    } else {
+      createThrowableMsg("$msg, Caused by: '${throwable.message}'", throwable.cause)
     }
-    return msg
   }
 }

src/jsTest/kotlin/io/github/oshai/kotlinlogging/SimpleJsTest.kt

@@ -28,6 +28,16 @@ class SimpleJsTest {
     assertEquals("info", appender.lastLevel)
   }
 
+  @Test
+  fun logThrowableTest() {
+    val errorLog = "Something Bad Happened"
+    val outerMessage = "Outer Message"
+    val innerMessage = "Inner Message"
+    val throwable = Throwable(message = outerMessage, cause = Throwable(message = innerMessage))
+    logger.error(throwable) { errorLog }
+    assertEquals("ERROR: [SimpleJsTest] $errorLog, Caused by: '$outerMessage', Caused by: '$innerMessage'", appender.lastMessage)
+  }
+
   @Test
   fun offLevelJsTest() {
     KotlinLoggingConfiguration.LOG_LEVEL = Level.OFF