Introduce Common readln() and readlnOrNull() top-level functions #KT-48456

libraries/stdlib/common/src/kotlin/ioH.kt

@@ -15,5 +15,29 @@ public expect fun println(message: Any?)
 /** Prints the given [message] to the standard output stream. */
 public expect fun print(message: Any?)
 
+/**
+ * Reads a line of input from the standard input stream and returns it,
+ * or throws a [RuntimeException] if EOF has already been reached when [readln] is called.
+ *
+ * LF or CRLF is treated as the line terminator. Line terminator is not included in the returned string.
+ *
+ * Currently this function is not supported in Kotlin/JS and throws [UnsupportedOperationException].
+ */
+@SinceKotlin("1.6")
+public expect fun readln(): String
+
+/**
+ * Reads a line of input from the standard input stream and returns it,
+ * or return `null` if EOF has already been reached when [readlnOrNull] is called.
+ *
+ * LF or CRLF is treated as the line terminator. Line terminator is not included in the returned string.
+ *
+ * Currently this function is not supported in Kotlin/JS and throws [UnsupportedOperationException].
+ */
+@SinceKotlin("1.6")
+public expect fun readlnOrNull(): String?
+
+internal class ReadAfterEOFException(message: String?) : RuntimeException(message)
+
 
 internal expect interface Serializable