Save TASTY in attribute of classfiles.

[DarkDimius]

Currently saves on all classfiles in the same compilation unit.
@odersky, feel free to take over

[xeno-by]

So if there are multiple classes in the same file, the same attribute will be written multiple times? Also, how is this supposed to be accessible at runtime?

[DarkDimius]

So if there are multiple classes in the same file, the same attribute will be written multiple times?

This should be fixed by either having a single top-level class per compilation unit after pickler, or pickler should prepare a map of what TASTY to save in which file.

Also, how is this supposed to be accessible at runtime?

Given this implementation, only using classloader.

This implementation is not thought as a long-term one, but to foster testing of TASTY in Dotty.
I would propose to discuss how should actual implementation look like on next TASTY meeting.

[odersky]

@DarkDimius Please review.

[xeno-by]

I pulled this PR together with #495 into master, then compiled Dotty, then ran it on a simple file, and it blew up. No idea whether I'm doing something wrong, or it's a genuine bug, but here's the log:

16:48 ~/Projects/dotty/sandbox (flatmap2015)$ cat Test.scala
class C {
  def x = 42
  def y = x
}
16:49 ~/Projects/dotty/sandbox (flatmap2015)$ dotc -Ytest-pickler Test.scala
Exception in thread "main" java.lang.AssertionError: assertion failed: denotation module class <empty> invalid in run 2. ValidFor: Period(1..4, run = 3)
    at scala.Predef$.assert(Predef.scala:165)
    at dotty.tools.dotc.core.Denotations$SingleDenotation.bringForward(Denotations.scala:508)
    at dotty.tools.dotc.core.Denotations$SingleDenotation.current(Denotations.scala:544)
    at dotty.tools.dotc.core.Symbols$Symbol.denot(Symbols.scala:370)
    at dotty.tools.dotc.core.SymDenotations$class.stillValid(SymDenotations.scala:49)
    at dotty.tools.dotc.core.Contexts$Context.stillValid(Contexts.scala:51)
    at dotty.tools.dotc.core.Types$NamedType.computeDenot(Types.scala:1220)
    at dotty.tools.dotc.core.Types$NamedType.denotAt(Types.scala:1206)
    at dotty.tools.dotc.core.Types$NamedType.denot(Types.scala:1194)
    at dotty.tools.dotc.ast.Trees$DenotingTree.denot(Trees.scala:270)
    at dotty.tools.dotc.ast.Trees$Tree.symbol(Trees.scala:187)
    at dotty.tools.dotc.ast.tpd$modsDeco.mods(tpd.scala:399)
    at dotty.tools.dotc.printing.RefinedPrinter$$anonfun$toText$2.apply(RefinedPrinter.scala:393)
    at dotty.tools.dotc.printing.RefinedPrinter$$anonfun$toText$2.apply(RefinedPrinter.scala:159)
    at dotty.tools.dotc.printing.PlainPrinter.controlled(PlainPrinter.scala:22)
    at dotty.tools.dotc.printing.RefinedPrinter.toText(RefinedPrinter.scala:159)