From ffaec276e1700a070e6f3c2a1f6103b6e7ae18e2 Mon Sep 17 00:00:00 2001
From: Justin Patterson <justin@scalawag.org>
Date: Tue, 10 Oct 2017 09:41:14 -0500
Subject: [PATCH] #128: prevent OutOfBoundsException on trailing newline

---
 .../util/parsing/input/OffsetPosition.scala    | 10 ++++++----
 .../parsing/input/OffsetPositionTest.scala     | 18 ++++++++++++++++++
 2 files changed, 24 insertions(+), 4 deletions(-)
 create mode 100644 shared/src/test/scala/scala/util/parsing/input/OffsetPositionTest.scala

diff --git a/shared/src/main/scala/scala/util/parsing/input/OffsetPosition.scala b/shared/src/main/scala/scala/util/parsing/input/OffsetPosition.scala
index c69fc4d9..7357880d 100644
--- a/shared/src/main/scala/scala/util/parsing/input/OffsetPosition.scala
+++ b/shared/src/main/scala/scala/util/parsing/input/OffsetPosition.scala
@@ -63,12 +63,14 @@ case class OffsetPosition(source: CharSequence, offset: Int) extends Position {
    * @return the line at `offset` (not including a newline)
    */
   def lineContents: String = {
-    val endIndex = if (source.charAt(index(line) - 1) == '\n') {
-      index(line) -  1
+    val lineStart = index(line - 1)
+    val lineEnd = index(line)
+    val endIndex = if ( lineStart < lineEnd && source.charAt(lineEnd - 1) == '\n') {
+      lineEnd - 1
     } else {
-      index(line)
+      lineEnd
     }
-    source.subSequence(index(line - 1), endIndex).toString
+    source.subSequence(lineStart, endIndex).toString
   }
 
   /** Returns a string representation of the `Position`, of the form `line.column`. */
diff --git a/shared/src/test/scala/scala/util/parsing/input/OffsetPositionTest.scala b/shared/src/test/scala/scala/util/parsing/input/OffsetPositionTest.scala
new file mode 100644
index 00000000..bbd9c9c4
--- /dev/null
+++ b/shared/src/test/scala/scala/util/parsing/input/OffsetPositionTest.scala
@@ -0,0 +1,18 @@
+package scala.util.parsing.input
+
+import org.junit.Test
+import org.junit.Assert.assertEquals
+
+class OffsetPositionTest {
+  @Test
+  def printLineContentsWithTrailingNewLine: Unit = {
+    val op = new OffsetPosition("\n", 1)
+    assertEquals(op.lineContents, "")
+  }
+
+  @Test
+  def printLineContentsWithEmptySource: Unit = {
+    val op = new OffsetPosition("", 0)
+    assertEquals(op.lineContents, "")
+  }
+}