Minor code improvements, add more test cases #KT-11208

Compare new readLine with the reference implementation in BufferedReader.

libraries/stdlib/src/kotlin/io/Console.kt

@@ -179,7 +179,6 @@ internal fun readLine(inputStream: InputStream, decoder: CharsetDecoder): String
         val length = position()
         val first = get(0)
         val second = get(1)
-        flip()
         when (length) {
             2 -> {
                 if (!(first == '\r' && second == '\n')) stringBuilder.append(first)
@@ -199,7 +198,7 @@ private fun CharsetDecoder.tryDecode(byteBuffer: ByteBuffer, charBuffer: CharBuf
         if (isError) throwException()
     }
     return (charBuffer.position() > positionBefore).also { isDecoded ->
-        byteBuffer.apply { if (isDecoded) clear() else flipBack() }
+        if (isDecoded) byteBuffer.clear() else byteBuffer.flipBack()
     }
 }
 
@@ -207,7 +206,7 @@ private fun CharBuffer.containsLineSeparator(): Boolean {
     return get(1) == '\n' || get(0) == '\n'
 }
 
-private fun Buffer.flipBack(): Buffer = apply {
+private fun Buffer.flipBack() {
     position(limit())
     limit(capacity())
 }

libraries/stdlib/test/io/Console.kt

@@ -1,20 +1,11 @@
 /*
- * Copyright 2010-2017 JetBrains s.r.o.
- *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- * http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
+ * Copyright 2010-2018 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license
+ * that can be found in the license/LICENSE.txt file.
  */
 
-package io
+@file:Suppress("INVISIBLE_REFERENCE", "INVISIBLE_MEMBER")
+@file:kotlin.jvm.JvmVersion
+package test.io
 
 import org.junit.Test
 import java.nio.charset.Charset
@@ -30,8 +21,19 @@ class ConsoleTest {
     }
 
     @Test
-    fun shouldReadOneLetter() {
-        testReadLine("a", listOf("a"))
+    fun shouldReadSingleLine() {
+        for (length in 1..3) {
+            val line = buildString { repeat(length) { append('a' + it) } }
+            testReadLine(line, listOf(line))
+        }
+    }
+
+    @Test
+    fun trailingEmptyLineIsIgnored() {
+        testReadLine(linuxLineSeparator, listOf(""))
+        testReadLine(windowsLineSeparator, listOf(""))
+        testReadLine("a$linuxLineSeparator", listOf("a"))
+        testReadLine("a$windowsLineSeparator", listOf("a"))
     }
 
     @Test
@@ -47,6 +49,9 @@ class ConsoleTest {
     @Test
     fun shouldReadConsecutiveEmptyLines() {
         testReadLine("$linuxLineSeparator$linuxLineSeparator", listOf("", ""))
+        testReadLine("$linuxLineSeparator$windowsLineSeparator", listOf("", ""))
+        testReadLine("$windowsLineSeparator$linuxLineSeparator", listOf("", ""))
+        testReadLine("$windowsLineSeparator$windowsLineSeparator", listOf("", ""))
     }
 
     @Test
@@ -62,14 +67,24 @@ class ConsoleTest {
     private fun testReadLine(text: String, expected: List<String>, charset: Charset = Charsets.UTF_8) {
         val actual = readLines(text, charset)
         assertEquals(expected, actual)
+        val referenceExpected = readLinesReference(text, charset)
+        assertEquals(referenceExpected, actual, "Comparing to reference readLine")
+
     }
 
     private fun readLines(text: String, charset: Charset): List<String> {
         text.byteInputStream(charset).use { stream ->
             val decoder = charset.newDecoder()
+            @Suppress("INVISIBLE_REFERENCE", "INVISIBLE_MEMBER")
             return generateSequence { readLine(stream, decoder) }.toList().also {
                 assertTrue("All bytes should be read") { stream.read() == -1 }
             }
         }
     }
+
+    private fun readLinesReference(text: String, charset: Charset): List<String> {
+        text.byteInputStream(charset).bufferedReader(charset).use { reader ->
+            return generateSequence { reader.readLine() }.toList()
+        }
+    }
 }