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Fix #7048: Check for splice stability #8097

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Merged
merged 2 commits into from
Jan 28, 2020
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Fix #7048: Check for splice stability #8097

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e29c481
Fix #7048: Check for splice stability
nicolasstucki Jan 27, 2020
a00d184
Add test
nicolasstucki Jan 28, 2020
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6 changes: 4 additions & 2 deletions compiler/src/dotty/tools/dotc/transform/PCPCheckAndHeal.scala
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Expand Up @@ -18,6 +18,7 @@ import dotty.tools.dotc.util.SourcePosition
import dotty.tools.dotc.util.Spans._
import dotty.tools.dotc.transform.SymUtils._
import dotty.tools.dotc.transform.TreeMapWithStages._
import dotty.tools.dotc.typer.Checking
import dotty.tools.dotc.typer.Implicits.SearchFailureType
import dotty.tools.dotc.typer.Inliner

Expand All @@ -31,7 +32,7 @@ import scala.annotation.constructorOnly
*
* Type healing consists in transforming a phase inconsistent type `T` into a splice of `implicitly[Type[T]]`.
*/
class PCPCheckAndHeal(@constructorOnly ictx: Context) extends TreeMapWithStages(ictx) {
class PCPCheckAndHeal(@constructorOnly ictx: Context) extends TreeMapWithStages(ictx) with Checking {
import tpd._

private val InAnnotation = Property.Key[Unit]()
Expand Down Expand Up @@ -212,7 +213,8 @@ class PCPCheckAndHeal(@constructorOnly ictx: Context) extends TreeMapWithStages(
val reqType = defn.QuotedTypeClass.typeRef.appliedTo(tp)
val tag = ctx.typer.inferImplicitArg(reqType, pos.span)
tag.tpe match
case _: TermRef =>
case tp: TermRef =>
checkStable(tp, pos)
Some(tag.select(tpnme.splice))
case _: SearchFailureType =>
levelError(sym, tp, pos,
Expand Down
1 change: 1 addition & 0 deletions compiler/test/dotc/pos-test-pickling.blacklist
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Expand Up @@ -10,6 +10,7 @@ t3486
t3612.scala
reference
scala-days-2019-slides
i7048e.scala

# Stale symbol: package object scala
seqtype-cycle
Expand Down
39 changes: 39 additions & 0 deletions tests/neg/i7048e.scala
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@@ -0,0 +1,39 @@
import scala.quoted.{given, _}

abstract class Test {
type T

val T: Type[T]
val getT: Type[T] = T // need this to avoid getting `null`
given Type[T] = getT

def foo with QuoteContext: Expr[Any] = {

val r = '{Option.empty[T]} // error

{
val t: Test = this
import t.{given}
println(summon[Type[t.T]].show)
// val r = '{Option.empty[t.T]} // access to value t from wrong staging level
val r2 = '{Option.empty[${t.T}]} // works
}

{
val r1 = '{Option.empty[${T}]} // works
val r2 = '{Option.empty[List[${T}]]} // works
// val r3 = '{summon[Type[${T}]]} // access to Test.this from wrong staging level
val r4 = '{summon[${T} <:< Any]} // error
}

{
val s = '{Option.empty[${T}]}
val r = '{identity($s)} // works
val r2 = '{identity(${s: Expr[Option[T]]})} // error // error
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It's not obvious why this is not accepted by the check.

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32 |      val r2 = '{identity[Option[T]](${s: Expr[Option[T]]})} // error // error
   |                                     ^^^^^^^^^^^^^^^^^^^^^
   |    (Test.this.given_Type_T : => quoted.Type[Test.this.T]) is not stable

All these can be fixed by making the given stable

val getT: Type[T] = T // need this to avoid getting `null`
given getT.type = getT

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Added an extra test for it

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Why it has to be stable?

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Type splices require a stable prefix to be correctly encoded. It also avoids having to deal with side effects in the transformation performed in ReifyQuotes. Most code receives the quoted type as a parameter and hence is stable.

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It's a restriction in TASTy? This is unprecedented in Scala, as usually only the path in types needs to be stable.

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This is a path in a type. A type that is inferred and then healed.

}

r
}
}

@main def main = ()
39 changes: 39 additions & 0 deletions tests/pos/i7048e.scala
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@@ -0,0 +1,39 @@
import scala.quoted.{given, _}

abstract class Test {
type T

val T: Type[T]
val getT: Type[T] = T // need this to avoid getting `null`
given getT.type = getT

def foo with QuoteContext: Expr[Any] = {

val r = '{Option.empty[T]}

{
val t: Test = this
import t.{given}
println(summon[Type[t.T]].show)
// val r = '{Option.empty[t.T]} // access to value t from wrong staging level
val r2 = '{Option.empty[${t.T}]}
}

{
val r1 = '{Option.empty[${T}]} // works
val r2 = '{Option.empty[List[${T}]]} // works
// val r3 = '{summon[Type[${T}]]} // access to Test.this from wrong staging level
val r4 = '{summon[${T} <:< Any]}
}

{
val s = '{Option.empty[${T}]}
val r = '{identity($s)} // works
val r2 = '{identity(${s: Expr[Option[T]]})}
}

r
}
}

@main def main = ()