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Fix #6588: synthesis of Type[T] should mapOver the type T #6589

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Fix #6588: synthesis of Type[T] should mapOver the type T #6589

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3b60d47
Fix #6588: synthesis of Type[T] should mapOver the type T
liufengyun May 30, 2019
ba19619
Fix CI
liufengyun May 30, 2019
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6 changes: 3 additions & 3 deletions compiler/src/dotty/tools/dotc/typer/Implicits.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -683,16 +683,16 @@ trait Implicits { self: Typer =>
case arg :: Nil if !arg.typeSymbol.is(Param) =>
object bindFreeVars extends TypeMap {
var ok = true
def apply(t: Type) = t match {
case t @ TypeRef(NoPrefix, _) =>
def apply(t: Type) = t.dealias match {
case t @ TypeRef(NoPrefix, _) if !ctx.inInlineMethod =>
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I did not understand the qualification !ctx.inInlineMethod. This looks fishy where it is. The other synthesized arguments do not depend on this test, so why would quoted.Type be different?

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In the case below in the outer match, we have the following logic:

https://github.com/lampepfl/dotty/blob/c165638cb46e498156bffcb5ad4ad4775d11bf35/compiler/src/dotty/tools/dotc/typer/Implicits.scala#L701-L702

I conjecture the motivation is that in inline methods, type parameters are treated as constants so that they are not restricted by phase consistency law, just like inline term parameters. /cc : @nicolasstucki

More concretely, without the test, the following test case i4514.scala fail:

object Foo {
  inline def foo[X](x: X): Unit = ${fooImpl('x)}
  def fooImpl[X: quoted.Type](x: X): quoted.Expr[Unit] = '{}
}

The implicit search first looks for Type[Expr[X]], the mapOver will reach X, and the implicit search for Type[X] fails.

inferImplicit(defn.QuotedTypeType.appliedTo(t), EmptyTree, span) match {
case SearchSuccess(tag, _, _) if tag.tpe.isStable =>
tag.tpe.select(defn.QuotedType_splice)
case _ =>
ok = false
t
}
case _ => t
case tp => mapOver(tp)
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what is the motivation to mapOver? This is suspicious. Is it to dealias further term as you have in the tests? Mapping over may also trigger another implicit search for parts of the type which should only be done in the PCP checks.

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@liufengyun liufengyun May 31, 2019 •
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If we do not mapOver, for the following code:

import scala.quoted._

inline def foo[T:Type]: Int = 10
def main = {
  type S = Int
  type V = List[S]
  foo[V]
}

It will generate an evidence in staging:

        type V = List[S]
        {
          val evidence$1: quoted.Type[List[S]] =
            '[List[quoted.Type[Int]#$splice]]
          10:Int
        }

The code will then crash ReifyQuotes.scala:153, as it assumes the prefixes of evidences are TermRefs.

}
}
val tag = bindFreeVars(arg)
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27 changes: 27 additions & 0 deletions tests/pos/i6588.scala
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Original file line number Diff line number Diff line change
@@ -0,0 +1,27 @@
import scala.quoted._

inline def foo[T:Type]: Int = 10

def main = {
type S = Int
foo[S]
foo[Int]

type T = Int => Int
foo[T]
foo[Int => Int]

type U = List[Int]
foo[U]
foo[List[Int]]

type N = List
foo[N]
foo[List]

type V = List[S]
foo[V]

type B = V => T
foo[B]
}
2 changes: 1 addition & 1 deletion tests/run-with-compiler/i4350.check
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@@ -1,2 +1,2 @@
(null: scala.Any).asInstanceOf[java.lang.Object]
(null: scala.Any).asInstanceOf[scala.Predef.String]
(null: scala.Any).asInstanceOf[java.lang.String]