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Scala compiler reports an error on for a wrong expression #9636

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scabug opened this issue Jan 30, 2016 · 4 comments
Closed

Scala compiler reports an error on for a wrong expression #9636

scabug opened this issue Jan 30, 2016 · 4 comments
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@som-snytt
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2.12.2

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@scabug
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scabug commented Jan 30, 2016

Scala 2.11.x for a function:

def isWrapper(is: FileInputStream): InputStream = {
  val pb = new PushbackInputStream(is, 2)
  val signature = new Array[Byte](2)
  pb.read(signature)
  pb.unread(signature)
  if (signature.sameElements(Array(0x1F, 0x8B))) {
    new GZIPInputStream(new BufferedInputStream(pb))
  } else {
    pb
  }
}

reports: a type was inferred to be AnyVal; this may indicate a programming error.

def isWrapper(is: FileInputStream): InputStream = {
                                               ^

Although an compilation problem corresponds to: signature.sameElements(Array(0x1F, 0x8B)) where second array is Array[Int] and not Array[Byte].

http://stackoverflow.com/questions/35104769/scala-anyval-inferred-instead-of-inputstream
@scabug
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scabug commented Jan 30, 2016

Imported From: https://issues.scala-lang.org/browse/SI-9636?orig=1
Reporter: Artem Oboturov (oboturov-at-gmail.com)
Affected Versions: 2.11.7
See #9211

@scabug
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scabug commented Jan 30, 2016

@som-snytt said:
The caret wanders:

Welcome to Scala 2.12.0-M3 (Java HotSpot(TM) 64-Bit Server VM, Java 1.8.0_60).
Type in expressions for evaluation. Or try :help.

scala> (new Array[Byte](2)).sameElements(Array(0x1F, 0x8B))
<console>:12: warning: a type was inferred to be `AnyVal`; this may indicate a programming error.
       (new Array[Byte](2)).sameElements(Array(0x1F, 0x8B))
                                              ^
res0: Boolean = false

scala> def f = if ((new Array[Byte](2)).sameElements(Array(0x1F, 0x8B))) true else false
<console>:11: warning: a type was inferred to be `AnyVal`; this may indicate a programming error.
       def f = if ((new Array[Byte](2)).sameElements(Array(0x1F, 0x8B))) true else false
           ^
f: Boolean

@scabug
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scabug commented Feb 1, 2016

@retronym said (edited on Feb 1, 2016 6:06:43 AM UTC):
methTypeArgs should accept an extra parameter with the position of the fn tree, rather than trying to reverse engineer the position by throwing darts, blindfolded, at context.tree.

      def argumentPosition(idx: Int): Position = context.tree match {
        case x: ValOrDefDef => x.rhs match {
          case Apply(fn, args) if idx < args.size => args(idx).pos
          case _                                  => context.tree.pos
        }
        case _ => context.tree.pos
      }
      if (settings.warnInferAny && context.reportErrors && canWarnAboutAny) {
        foreachWithIndex(targs) ((targ, idx) =>
          targ.typeSymbol match {
            case sym @ (AnyClass | AnyValClass) =>
              reporter.warning(argumentPosition(idx), s"a type was inferred to be `${sym.name}`; this may indicate a programming error.")
            case _ =>
          }
        )
      }

@scabug
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scabug commented Nov 19, 2016

@som-snytt said:
scala/scala#5546

@scabug scabug closed this as completed Feb 16, 2017
@scabug scabug added this to the 2.12.2 milestone Apr 7, 2017
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