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[backport] SI-7902 Fix spurious kind error due to an unitialized symbol

Tracked down this error:

    <none> is invariant, but type Y2 is declared covariant
    <none>'s bounds<notype> are stricter than type X2's declared bounds >: Nothing <: Any, <none>'s bounds<notype> are stricter than type Y2's declared bounds >: Nothing <: Any

to `Symbol#typeParams` returning `List(NoSymbol)` if the symbol
was not initialized.

This happends in the enclosed test for:

    // checkKindBoundsHK()
    hkArgs   = List(type M3)
    hkParams = List(type M2)

This commit forces the symbol of the higher-kinded type argument
before checking kind conformance.

A little backstory:

The `List(NoSymbol)` arises from:

    class PolyTypeCompleter... {
      // @M. If `owner` is an abstract type member, `typeParams` are all NoSymbol (see comment in `completerOf`),
      // otherwise, the non-skolemized (external) type parameter symbols
      override val typeParams = tparams map (_.symbol)

The variation that triggers this problem gets into the kind
conformance checks quite early on, during naming of:

    private[this] val x = ofType[InSeq]

The inferred type of which is forced during:

    def addDerivedTrees(typer: Typer, stat: Tree): List[Tree] = stat match {
      case vd @ ValDef(mods, name, tpt, rhs) if !noFinishGetterSetter(vd) =>
        // If we don't save the annotations, they seem to wander off.
        val annotations = stat.symbol.initialize.annotations

(cherry picked from commit 03a06e0)
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1 parent 5720e97 commit 5f4011ef2969e4c4ac93f570bef45e9afb65bb9a @retronym retronym committed Oct 9, 2013
Showing with 19 additions and 1 deletion.
  1. +2 −1 src/reflect/scala/reflect/internal/Kinds.scala
  2. +17 −0 test/files/pos/t7902.scala
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3 src/reflect/scala/reflect/internal/Kinds.scala
@@ -184,6 +184,7 @@ trait Kinds {
)
}
else {
+ hkarg.initialize // SI-7902 otherwise hkarg.typeParams yields List(NoSymbol)!
debuglog("checkKindBoundsHK recursing to compare params of "+ hkparam +" with "+ hkarg)
kindErrors ++= checkKindBoundsHK(
hkarg.typeParams,
@@ -229,4 +230,4 @@ trait Kinds {
}
}
}
-}
+}
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17 test/files/pos/t7902.scala
@@ -0,0 +1,17 @@
+import scala.language.higherKinds
+
+object Bug {
+ class Tag[W[M1[X1]]]
+
+ def ofType[W[M2[X2]]]: Tag[W] = ???
+ type InSeq [M3[X3]] = Some[M3[Any]]
+
+ // fail
+ val x = ofType[InSeq]
+
+ // okay
+ val y: Any = ofType[InSeq]
+ object T {
+ val z = ofType[InSeq]
+ }
+}

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