SI-8205 Avoid long, slow march to AIIOBE in SourceFile#lineContent

Fixing a regression from SI-8015.

The failure mode is kind of amusing: a while loop in `lineToString`
would count all the way to `Int.MaxValue`, and integer overflow
would foil a bounds check when looking for the 'LF' in 'CR'-'LF'.

Given that we're not a style checker to enforce that source files
end in a new-line, this commit accounts for EOF, and fixed the
overflow problem too.

A JUnit test exercises the bug and a few other variations of
`lineContent`.

While i was in the neighbourhood, I opted for a more efficient
means to slice out that line.

1 files changed, 3 insertions, 3 deletions

diff --git a/src/reflect/scala/reflect/internal/util/SourceFile.scala b/src/reflect/scala/reflect/internal/util/SourceFile.scala
index 9866b043bb..add072aa71 100644
--- a/src/reflect/scala/reflect/internal/util/SourceFile.scala
+++ b/src/reflect/scala/reflect/internal/util/SourceFile.scala
@@ -40,8 +40,8 @@ abstract class SourceFile {
   def lineToString(index: Int): String = {
     val start = lineToOffset(index)
     var end = start
-    while (!isEndOfLine(end)) end += 1
-    content.slice(start, end) mkString ""
+    while (!isEndOfLine(end) && end <= length) end += 1
+    new String(content, start, end - start)
   }
 
   @tailrec
@@ -136,7 +136,7 @@ class BatchSourceFile(val file : AbstractFile, val content0: Array[Char]) extend
 
   private def charAtIsEOL(idx: Int)(p: Char => Boolean) = {
     // don't identify the CR in CR LF as a line break, since LF will do.
-    def notCRLF0 = content(idx) != CR || idx + 1 >= length || content(idx + 1) != LF
+    def notCRLF0 = content(idx) != CR || !content.isDefinedAt(idx + 1) || content(idx + 1) != LF
 
     idx < length && notCRLF0 && p(content(idx))
   }