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Fix #2973: Check variances of class parents #4057

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Fix #2973: Check variances of class parents #4057

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2 changes: 1 addition & 1 deletion compiler/src/dotty/tools/dotc/typer/Typer.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -1509,11 +1509,11 @@ class Typer extends Namer
checkNoDoubleDefs(cls)
val impl1 = cpy.Template(impl)(constr1, parents1, self1, body1)
.withType(dummy.termRef)
checkVariance(impl1)
if (!cls.is(AbstractOrTrait) && !ctx.isAfterTyper)
checkRealizableBounds(cls, cdef.namePos)
if (cls.is(Case) && cls.derivesFrom(defn.EnumClass)) checkEnum(cdef, cls)
val cdef1 = assignType(cpy.TypeDef(cdef)(name, impl1), cls)
checkVariance(cdef1)
if (ctx.phase.isTyper && cdef1.tpe.derivesFrom(defn.DynamicClass) && !ctx.dynamicsEnabled) {
val isRequired = parents1.exists(_.tpe.isRef(defn.DynamicClass))
ctx.featureWarning(nme.dynamics.toString, "extension of type scala.Dynamic", isScala2Feature = true,
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10 changes: 6 additions & 4 deletions compiler/src/dotty/tools/dotc/typer/VarianceChecker.scala
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Expand Up @@ -93,8 +93,8 @@ class VarianceChecker()(implicit ctx: Context) {
this(status, tp.resultType) // params will be checked in their TypeDef or ValDef nodes.
case AnnotatedType(_, annot) if annot.symbol == defn.UncheckedVarianceAnnot =>
status
//case tp: ClassInfo =>
// ??? not clear what to do here yet. presumably, it's all checked at local typedefs
case tp: ClassInfo =>
foldOver(status, tp.classParents)
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This visit sees the parent classes, but stripped of any annotations!

case _ =>
foldOver(status, tp)
}
Expand Down Expand Up @@ -132,14 +132,16 @@ class VarianceChecker()(implicit ctx: Context) {
ctx.debuglog(s"Skipping variance check of ${sym.showDcl}")
case tree: TypeDef =>
checkVariance(sym, tree.pos)
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On tests/pos/Iterable.scala we get an error inside this call (going through tp.classParents), because sym contains the parens but without annotations!

tree.rhs match {
case rhs: Template => traverseChildren(rhs)
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Here traverseChildren sees parents (in the form of a constructor call), but this Traverser ignores terms and only looks at definitions...

case _ =>
}
case tree: ValDef =>
checkVariance(sym, tree.pos)
case DefDef(_, tparams, vparamss, _, _) =>
checkVariance(sym, tree.pos)
tparams foreach traverse
vparamss foreach (_ foreach traverse)
case Template(_, _, _, body) =>
traverseChildren(tree)
case _ =>
}
}
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2 changes: 2 additions & 0 deletions tests/neg/i2973.scala
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@@ -0,0 +1,2 @@
class Foo[U]
class Bar[-T] extends Foo[T] // error: contravariant type T occurs in invariant position