SI-8015 Unprintables in messages

The line content to display should include the whole line,
inclusive of embedded line breaks, and any control chars
should be displayed in unicode escape.

3 files changed, 17 insertions, 4 deletions

diff --git a/src/reflect/scala/reflect/internal/util/Position.scala b/src/reflect/scala/reflect/internal/util/Position.scala
index 15cfda26b5..dbee31bfca 100644
--- a/src/reflect/scala/reflect/internal/util/Position.scala
+++ b/src/reflect/scala/reflect/internal/util/Position.scala
@@ -207,7 +207,16 @@ private[util] trait InternalPositionImpl {
   def showError(msg: String): String = finalPosition match {
     case FakePos(fmsg) => s"$fmsg $msg"
     case NoPosition    => msg
-    case pos           => s"${pos.line}: $msg\n${pos.lineContent}\n${pos.lineCarat}"
+    case pos           => f"${pos.line}: $msg%n${u(pos.lineContent)}%n${pos.lineCarat}"
+  }
+  private def u(s: String) = {
+    def uu(c: Int) = f"\\u$c%04x"
+    def uable(c: Int) = (c < 0x20 && c != '\t') || c == 0x7F
+    if (s exists (c => uable(c))) {
+      val sb = new StringBuilder
+      s foreach (c => sb append (if (uable(c)) uu(c) else c))
+      sb.toString
+    } else s
   }
   def showDebug: String = toString
   def show = (
diff --git a/src/reflect/scala/reflect/internal/util/SourceFile.scala b/src/reflect/scala/reflect/internal/util/SourceFile.scala
index 1da334d41f..39c4ac8a95 100644
--- a/src/reflect/scala/reflect/internal/util/SourceFile.scala
+++ b/src/reflect/scala/reflect/internal/util/SourceFile.scala
@@ -37,8 +37,12 @@ abstract class SourceFile {
   override def toString() = file.name
   def path = file.path
 
-  def lineToString(index: Int): String =
-    content drop lineToOffset(index) takeWhile (c => !isLineBreakChar(c.toChar)) mkString ""
+  def lineToString(index: Int): String = {
+    val start = lineToOffset(index)
+    var end = start
+    while (!isEndOfLine(end)) end += 1
+    content.slice(start, end) mkString ""
+  }
 
   @tailrec
   final def skipWhitespace(offset: Int): Int =
diff --git a/test/files/neg/t8015-ffb.check b/test/files/neg/t8015-ffb.check
index 90c8d045b4..9b2171ea47 100644
--- a/test/files/neg/t8015-ffb.check
+++ b/test/files/neg/t8015-ffb.check
@@ -1,5 +1,5 @@
 t8015-ffb.scala:10: warning: side-effecting nullary methods are discouraged: suggest defining as `def w()` instead
-  def w = { x
+  def w = { x\u000c() }       // ^L is colored blue on this screen, hardly visible
       ^
 error: No warnings can be incurred under -Xfatal-warnings.
 one warning found