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TypeMap::noChangeToSymbols discards changes hidden behind symbol #8166

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scabug opened this issue Jan 21, 2014 · 2 comments
Open

TypeMap::noChangeToSymbols discards changes hidden behind symbol #8166

scabug opened this issue Jan 21, 2014 · 2 comments
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@scabug
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scabug commented Jan 21, 2014

In TypeMap, the following optimization is too eager:

protected def noChangeToSymbols(origSyms: List[Symbol]) =
      origSyms forall (sym => sym.info eq this(sym.info))

sym.info may still change indirectly, when
sym.info.typeSymbol.info ne this(sym.info.typeSymbol.info)

It turns out it's more than an optimization, as simply setting it to false causes other problems.

repro:

// derived from a real-world Slick app (support #3035)
// running Test should not throw a java.lang.ClassFormatError: Duplicate method name&signature in class file Test$$anonfun$1 
// workaround: uncomment type arg to list below

class AbstractTable[T] { type TableElementType }
class Table[T] extends AbstractTable[T] { type TableElementType = T }

class Query[E, U]
class TableQuery[E <: AbstractTable[_]] extends Query[E, E#TableElementType]

object Test extends App {
  object MyTable extends TableQuery[Table[Long]]

  def list[R](q: Query[_, R]): List[R] = Nil
  list/*[Long]*/(MyTable) collect { case x => x }
}
@scabug
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scabug commented Jan 21, 2014

Imported From: https://issues.scala-lang.org/browse/SI-8166?orig=1
Reporter: @adriaanm
Affected Versions: 2.10.3
See #8114
Clones #8114

@scabug
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scabug commented Jan 21, 2014

@retronym said:
Here's a (contrived) TypeMap that might help this discussion. It tries, in one pass, to substitute Longs for Ints and type parameters with their upper bounds:

scala> object map extends TypeMap {
  def apply(tp: Type) = tp match {
    case TypeRef(pre, sym, args) if sym == IntClass   => LongClass.tpe
    case TypeRef(_, sym, args) if sym.isTypeParameter => mapOver(tp.bounds.hi)
    case x => mapOver(x)
  }
}
defined object map

scala> trait T { def m[A <: Int](a: A) }
defined trait T

scala> val m = typeOf[T].member(TermName("m"))
m: $r.intp.global.Symbol = method m

scala> map(m.info)
res31: $r.intp.global.Type = [A <: Long](a: Int)Unit

We could substitute tparams -> tparams1 in result before applying the TypeMap to make this work. But I'm not sure thats the right thing to do.

@scabug scabug added the critical label Apr 7, 2017
@scabug scabug added this to the Backlog milestone Apr 7, 2017
@retronym retronym mentioned this issue Aug 28, 2018
Merged
@adriaanm adriaanm removed their assignment Sep 28, 2018
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@adriaanm @SethTisue @scabug