feat: add wasmWasi target with console appender and tests (#551)

* feat: add wasmWasi target with console appender and tests
* feat(wasmWasi): smarter logger name resolution with .kt stacktrace fallback; chore: remove changelog note

Author: oshai

build.gradle.kts

@@ -87,6 +87,11 @@ kotlin {
             }
         }
     }
+    @OptIn(org.jetbrains.kotlin.gradle.ExperimentalWasmDsl::class)
+    wasmWasi { // console based WASI target
+        // Use nodejs as runtime env for tests & distribution (WASI support via node --experimental-wasi-unstable-preview1)
+        nodejs()
+    }
     androidTarget {
         publishLibraryVariants("release", "debug")
     }
@@ -218,6 +223,14 @@ kotlin {
                 implementation(kotlin("test-wasm-js"))
             }
         }
+        val wasmWasiMain by getting {
+            dependsOn(directMain)
+        }
+        val wasmWasiTest by getting {
+            dependencies {
+                implementation(kotlin("test-wasm-wasi"))
+            }
+        }
         val nativeMain by creating {
             dependsOn(directMain)
         }

src/wasmWasiMain/kotlin/io/github/oshai/kotlinlogging/ConsoleOutputAppender.kt

@@ -0,0 +1,15 @@
+package io.github.oshai.kotlinlogging
+
+// Simple console appender for WASI target relying on stdout
+public object ConsoleOutputAppender : FormattingAppender() {
+  override fun logFormattedMessage(loggingEvent: KLoggingEvent, formattedMessage: Any?) {
+    when (loggingEvent.level) {
+      Level.TRACE,
+      Level.DEBUG,
+      Level.INFO,
+      Level.WARN,
+      Level.ERROR -> println(formattedMessage)
+      Level.OFF -> Unit
+    }
+  }
+}

src/wasmWasiMain/kotlin/io/github/oshai/kotlinlogging/KotlinLoggingConfiguration.kt

@@ -0,0 +1,7 @@
+package io.github.oshai.kotlinlogging
+
+public actual object KotlinLoggingConfiguration {
+  public actual var logLevel: Level = Level.INFO
+  public actual var formatter: Formatter = DefaultMessageFormatter(includePrefix = true)
+  public actual var appender: Appender = ConsoleOutputAppender
+}

src/wasmWasiMain/kotlin/io/github/oshai/kotlinlogging/internal/KLoggerNameResolver.kt

@@ -0,0 +1,50 @@
+package io.github.oshai.kotlinlogging.internal
+
+private const val NO_CLASS = ""
+
+internal actual object KLoggerNameResolver {
+  // In WASI the stacktrace is often empty; derive from lambda's synthetic class name when possible.
+  internal actual fun name(func: () -> Unit): String {
+    val qn = func::class.qualifiedName
+    // Examples:
+    //  - "SimpleWasmWasiTest$anonymousClassPropLogger$lambda" -> "SimpleWasmWasiTest"
+    //  - "anonymousFilePropLogger$lambda" -> unknown (should NOT use this)
+    if (qn != null) {
+      val base = qn.substringBefore('$')
+      // Heuristic: class names in Kotlin usually start with uppercase; avoid returning synthetic
+      // top-level property names like 'anonymousFilePropLogger'.
+      if (base.isNotEmpty() && base.first().isUpperCase()) {
+        return base
+      }
+    }
+
+    // Fallback: Try to derive from stack by locating a .kt source file and using its base name.
+    val fileName = tryExtractFileNameFromJsStack()
+    return fileName ?: NO_CLASS
+  }
+
+  private fun tryExtractFileNameFromJsStack(): String? {
+    val st = Exception().stackTraceToString()
+    if (st.isBlank()) return null
+    // Try to find something like '/path/.../SimpleWasmWasiTest.kt' or 'SimpleWasmWasiTest.kt'
+    val regex = Regex("""([A-Za-z0-9_]+)\.kt""")
+    for (line in st.lineSequence()) {
+      val match = regex.find(line)
+      if (match != null) {
+        val base = match.groupValues[1]
+        if (base.isNotEmpty()) return base
+      }
+    }
+    // Fallback similar to jsMain approach: take the token after last '/' and before '.kt'.
+    for (line in st.lineSequence()) {
+      if (".kt" in line) {
+        val preKt = line.substringBefore(".kt")
+        val afterSlash = preKt.substringAfterLast('/')
+        val afterBackslash = afterSlash.substringAfterLast('\\')
+        val afterDot = afterBackslash.substringAfterLast('.')
+        if (afterDot.isNotEmpty()) return afterDot
+      }
+    }
+    return null
+  }
+}

src/wasmWasiTest/kotlin/io/github/oshai/kotlinlogging/SimpleWasmWasiTest.kt

@@ -0,0 +1,97 @@
+package io.github.oshai.kotlinlogging
+
+import kotlin.test.*
+
+private val namedLogger = KotlinLogging.logger("SimpleWasmWasiTest")
+private val anonymousFilePropLogger = KotlinLogging.logger {}
+
+// Create a logger inside a top-level function to exercise the stacktrace-based fallback
+private fun createAnonymousFunctionLogger() = KotlinLogging.logger {}
+
+class SimpleWasmWasiTest {
+  private lateinit var appender: SimpleAppender
+  private val anonymousClassPropLogger = KotlinLogging.logger {}
+
+  @BeforeTest
+  fun setup() {
+    appender = createAppender()
+    KotlinLoggingConfiguration.appender = appender
+  }
+
+  @AfterTest
+  fun cleanup() {
+    KotlinLoggingConfiguration.appender = ConsoleOutputAppender
+    KotlinLoggingConfiguration.logLevel = Level.INFO
+  }
+
+  @Test
+  fun simpleWasiTest() {
+    assertEquals("SimpleWasmWasiTest", namedLogger.name)
+    namedLogger.info { "info msg" }
+    assertEquals("INFO: [SimpleWasmWasiTest] info msg", appender.lastMessage)
+    assertEquals("info", appender.lastLevel)
+  }
+
+  @Test
+  fun anonymousFilePropWasiTest() {
+    // On WASI, stack traces are often unavailable; top-level property name may be empty.
+    val n = anonymousFilePropLogger.name
+    if (n.isNotEmpty()) {
+      assertEquals("SimpleWasmWasiTest", n)
+    }
+    anonymousFilePropLogger.info { "info msg" }
+    val expected =
+      if (n.isNotEmpty()) {
+        "INFO: [SimpleWasmWasiTest] info msg"
+      } else {
+        "INFO: [] info msg"
+      }
+    assertEquals(expected, appender.lastMessage)
+  }
+
+  @Test
+  fun anonymousClassPropWasiTest() {
+    assertEquals("SimpleWasmWasiTest", anonymousClassPropLogger.name)
+    anonymousClassPropLogger.info { "info msg" }
+    assertEquals("INFO: [SimpleWasmWasiTest] info msg", appender.lastMessage)
+  }
+
+  @Test
+  fun anonymousFunctionWasiTest_stacktraceFallback() {
+    // This aims to cover the new fallback that parses the .kt filename from the stacktrace.
+    val logger = createAnonymousFunctionLogger()
+    val n = logger.name
+    if (n.isNotEmpty()) {
+      assertEquals("SimpleWasmWasiTest", n)
+    }
+    logger.info { "function msg" }
+    val expected =
+      if (n.isNotEmpty()) {
+        "INFO: [SimpleWasmWasiTest] function msg"
+      } else {
+        "INFO: [] function msg"
+      }
+    assertEquals(expected, appender.lastMessage)
+  }
+
+  @Test
+  fun offLevelWasiTest() {
+    KotlinLoggingConfiguration.logLevel = Level.OFF
+    assertTrue(namedLogger.isLoggingOff())
+    namedLogger.error { "error msg" }
+    assertEquals("NA", appender.lastMessage)
+    assertEquals("NA", appender.lastLevel)
+  }
+
+  private fun createAppender(): SimpleAppender = SimpleAppender()
+
+  class SimpleAppender : Appender {
+    var lastMessage: String = "NA"
+    var lastLevel: String = "NA"
+
+    override fun log(loggingEvent: KLoggingEvent) {
+      lastMessage = DefaultMessageFormatter(includePrefix = true).formatMessage(loggingEvent)
+      lastLevel = loggingEvent.level.name.lowercase()
+    }
+  }
+}