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Type inference issue with 2.9.0.RC3 for arities 21 and 22, but not 1 to 20 #4545

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scabug opened this issue May 4, 2011 · 7 comments
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@scabug scabug commented May 4, 2011

[Edited for brevity and accuracy.]

Compiles with 2.8.1, fails with 2.9.0.RC1 through current.

object Test {  
  def f[A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P, Q, R, S, T](table: Tuple20[A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P, Q, R, S, T])(fun: (A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P, Q, R, S, T) => Unit) {
  }
  def g[A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P, Q, R, S, T, U](table: Tuple21[A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P, Q, R, S, T, U])(fun: (A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P, Q, R, S, T, U) => Unit) {
  }

  def g20 = f(
    (  1,   1,   1,   1,   1,   1,   1,   1,   1,   1,   1,   1,   1,   1,   1,   1,   1,   1,   1,   1)
  ) { case ((a, b, c, d, e, f, g, h, i, j, k, l, m, n, o, p, q, r, s, t)) => () }
  
  def g21 = g(
      (1,   1,   1,   1,   1,   1,   1,   1,   1,   1,   1,   1,   1,   1,   1,   1,   1,   1,   1,   1,   1)
  ) { case ((a, b, c, d, e, f, g, h, i, j, k, l, m, n, o, p, q, r, s, t, u)) => () }
}

Failure in rc:

c.scala:13: error: missing parameter type for expanded function
The argument types of an anonymous function must be fully known. (SLS 8.5)
Expected type was: Function21[Int,Int,Int,Int,Int,Int,Int,Int,Int,Int,Int,Int,Int,Int,Int,Int,Int,Int,Int,Int,Int,Unit]
  ) { case ((a, b, c, d, e, f, g, h, i, j, k, l, m, n, o, p, q, r, s, t, u)) => () }
    ^
one error found
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@scabug scabug commented May 4, 2011

Imported From: https://issues.scala-lang.org/browse/SI-4545?orig=1
Reporter: @bvenners
Other Milestones: 2.10.0
Attachments:

  • RC3Bug.scala (created on May 4, 2011 5:34:34 PM UTC, 26874 bytes)
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@scabug scabug commented May 4, 2011

@paulp said:
Fascinating bug. However it is in RC1. I'm pretty confident of that fact because I can reproduce the absence of the bug in 2.8.1, but all the rcs show the bug.

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@scabug scabug commented May 4, 2011

@paulp said:
Reduced by a couple orders of magnitude, and removing the red herrings of implicit conversions and overloaded varargs polymorphic applies, and changed to use a partial function because the error message is much clearer (and shorter.)

object Test {  
  def f[A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P, Q, R, S, T](table: Tuple20[A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P, Q, R, S, T])(fun: (A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P, Q, R, S, T) => Unit) {
  }
  def g[A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P, Q, R, S, T, U](table: Tuple21[A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P, Q, R, S, T, U])(fun: (A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P, Q, R, S, T, U) => Unit) {
  }

  def g20 = f(
    (  1,   1,   1,   1,   1,   1,   1,   1,   1,   1,   1,   1,   1,   1,   1,   1,   1,   1,   1,   1)
  ) { case ((a, b, c, d, e, f, g, h, i, j, k, l, m, n, o, p, q, r, s, t)) => () }
  
  def g21 = g(
      (1,   1,   1,   1,   1,   1,   1,   1,   1,   1,   1,   1,   1,   1,   1,   1,   1,   1,   1,   1,   1)
  ) { case ((a, b, c, d, e, f, g, h, i, j, k, l, m, n, o, p, q, r, s, t, u)) => () }
}

This compiles in 2.8. In rc1 through current it fails:

c.scala:13: error: missing parameter type for expanded function
The argument types of an anonymous function must be fully known. (SLS 8.5)
Expected type was: Function21[Int,Int,Int,Int,Int,Int,Int,Int,Int,Int,Int,Int,Int,Int,Int,Int,Int,Int,Int,Int,Int,Unit]
  ) { case ((a, b, c, d, e, f, g, h, i, j, k, l, m, n, o, p, q, r, s, t, u)) => () }
    ^
one error found
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@scabug scabug commented May 10, 2011

@dragos said:
Adriaan, can you please have a look?

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@scabug scabug commented May 10, 2011

@adriaanm said:
classic off-by-one, I'd say (as well as the poster child for sane variable names):

now:

    def isFunctionType(tp: Type): Boolean = tp.normalize match {
      case TypeRef(_, sym, args) if args.nonEmpty =>
        val len = args.length
        len < MaxFunctionArity && sym == FunctionClass(len - 1)
      case _ =>
        false
    }

i claim this is more clear as well as correct:

    def isFunctionType(tp: Type): Boolean = tp.normalize match {
      case TypeRef(_, sym, args) if args.nonEmpty =>
        val arity = args.length - 1
        arity <= MaxFunctionArity && sym == FunctionClass(arity)
      case _ =>
        false
    }
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@scabug scabug commented May 12, 2011

@paulp said:
Replying to [comment:5 moors]:

classic off-by-one, I'd say (as well as the poster child for sane variable names):

But how will lenny respond to this blatant attempt to exclude him?

Now I see how creates a class "off-by-two" bug (as this fails at both 21 and 22.) One takes this:

  args.length - 1 <= MaxFunctionArity

And cleverly turns it into this:

val len = args.length
len < MaxFunctionArity

Adding one and changing from <= to < must cancel each other out, right?

At least the perpetrator of this was nobly trying to make things faster by eliminating some of the many calls to list.length. He deserves a medal, not your fencepost scorn.

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@scabug scabug commented Mar 30, 2012

@paulp said:
Fixed in 75e584bd0c , sorry it took so long.

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