Improved @tailrec error messages to specify the...

Improved @tailrec error messages to specify the reason. In the process
fixed old bug involving tail call transformation. Closes #3275, #2018.
Review by dragos.

1 files changed, 28 insertions, 16 deletions

diff --git a/test/files/neg/tailrec.scala b/test/files/neg/tailrec.scala
index 4c45672f93..a77f439cfe 100644
--- a/test/files/neg/tailrec.scala
+++ b/test/files/neg/tailrec.scala
@@ -1,53 +1,65 @@
 import scala.annotation.tailrec
 
 // putting @tailrec through the paces
-object Main {
-  @tailrec
-  def facfail(n: Int): Int =
-    if (n == 0) 1
-    else n * facfail(n - 1)
-
+object Winners {
   @tailrec
   def facsucc(n: Int, acc: Int): Int =
     if (n == 0) acc
     else facsucc(n - 1, n * acc)
 
-  @tailrec def loopy1(x: Int): Int = loopy1(x - 1)
+  @tailrec def loopsucc1(x: Int): Int = loopsucc1(x - 1)
+  @tailrec def loopsucc2[T](x: Int): Int = loopsucc2[T](x - 1)
 
   def ding {
     object dong {
-      @tailrec def loopy2(x: Int): Int = loopy2(x)
+      @tailrec def loopsucc3(x: Int): Int = loopsucc3(x)
     }
     ()
   }
 
   def inner(q: Int) = {
     @tailrec
-    def loopy3(x: Int): Int = loopy3(x + 1)
+    def loopsucc4(x: Int): Int = loopsucc4(x + 1)
 
-    loopy3(q)
+    loopsucc4(q)
+  }
+
+  object innerBob {
+    @tailrec def loopsucc5(x: Int): Int = loopsucc5(x)
   }
 }
 
-class Bob {
-  // these should work
+class Winners {
   @tailrec private def succ1(x: Int): Int = succ1(x)
   @tailrec final def succ2(x: Int): Int = succ2(x)
   @tailrec final def succ3[T](in: List[T], acc: List[T]): List[T] = in match {
     case Nil      => Nil
     case x :: xs  => succ3(xs, x :: acc)
   }
+}
 
+object Failures {
+  @tailrec
+  def facfail(n: Int): Int =
+    if (n == 0) 1
+    else n * facfail(n - 1)
+}
+
+class Failures {
   // not private, not final
   @tailrec def fail1(x: Int): Int = fail1(x)
 
   // a typical between-chair-and-keyboard error
-  @tailrec def fail2[T](xs: List[T]): List[T] = xs match {
+  @tailrec final def fail2[T](xs: List[T]): List[T] = xs match {
     case Nil      => Nil
-    case x :: xs  => x :: fail2(xs)
+    case x :: xs  => x :: fail2[T](xs)
   }
 
-  object innerBob {
-    @tailrec def succ4(x: Int): Int = succ4(x)
+  // unsafe
+  @tailrec final def fail3[T](x: Int): Int = fail3(x - 1)
+
+  // unsafe
+  class Tom[T](x: Int) {
+    @tailrec final def fail4[U](other: Tom[U], x: Int): Int = other.fail4[U](other, x - 1)
   }
 }