TimberLinkingTree.kt

class TimberLinkingTree : Timber.Tree() {
    private val CALL_STACK_INDEX = 4
    private val ANONYMOUS_CLASS = Pattern.compile("(\\$\\d+)+$")

    override fun log(priority: Int, tag: String, message: String, t: Throwable) {
        val stackTrace = Throwable().stackTrace
        if (stackTrace.size <= CALL_STACK_INDEX) {
            throw IllegalStateException(
                    "Synthetic stacktrace didn't have enough elements: are you using proguard?")
        }
        val clazz = extractClassName(stackTrace[CALL_STACK_INDEX])
        val lineNumber = stackTrace[CALL_STACK_INDEX].lineNumber
        val formatted = ".($clazz.java:$lineNumber) - $message"
        super.log(priority, tag, formatted, t)
    }

    /**
     * Extract the class name without any anonymous class suffixes (e.g., `Foo$1`
     * becomes `Foo`).
     */
    private fun extractClassName(element: StackTraceElement): String {
        var tag = element.className
        val m = ANONYMOUS_CLASS.matcher(tag)
        if (m.find()) {
            tag = m.replaceAll("")
        }
        return tag.substring(tag.lastIndexOf('.') + 1)
    }
}