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Forbid StringConstant(null) #23064

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Merged
merged 3 commits into from
May 9, 2025
Merged

Forbid StringConstant(null) #23064

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bbe2dde
Fix `Constant` tag of `Expr(null: String)`
mbovel Apr 28, 2025
e0fbfde
Accept `null` in `StringToExpr` but not in `StringConstant`
mbovel Apr 30, 2025
2e3c803
Do not handle `null` in `StringToExpr`
mbovel May 8, 2025
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2 changes: 1 addition & 1 deletion compiler/src/scala/quoted/runtime/impl/QuotesImpl.scala
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Expand Up @@ -2529,7 +2529,7 @@ class QuotesImpl private (using val ctx: Context) extends Quotes, QuoteUnpickler
end StringConstantTypeTest

object StringConstant extends StringConstantModule:
def apply(x: String): StringConstant = dotc.core.Constants.Constant(x)
def apply(x: String): StringConstant = dotc.core.Constants.Constant(x: Any)
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This is a fix to what I believe is a soundness hole in explicit nulls. I'm going to try to have another example with more details about this soundness issue.

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If there is unsafe data feed into explicit nulls, there is nothing we can do other than runtime check.

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If this is a valid fix, then comments is needed inline

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May be it is better to add:

object dotc.core.Constants.Constant{
  val nullConstant: Constant  = new Constant(null, NullTag)
}

def apply(x: String): StringConstant = if (x==null) {dotc.core.Constants.nullConstant} else {dotc.core.Constants.Constant(x)}

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@mbovel mbovel Apr 30, 2025 •
edited
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I was also surprised when I discovered true/false/null constants are not re-used/interned/hash-consed. I don't know if that would have a significant impact. I think this could be discussed in a separate issue or PR.

def unapply(constant: StringConstant): Some[String] = Some(constant.stringValue)
end StringConstant

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1 change: 1 addition & 0 deletions tests/run-macros/i23008.check
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@@ -0,0 +1 @@
null
12 changes: 12 additions & 0 deletions tests/run-macros/i23008/Macros_1.scala
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@@ -0,0 +1,12 @@
import scala.quoted.*

object Macros {
inline def buildString = ${buildStringCode}

def buildStringCode(using Quotes): Expr[String] = {
import quotes.reflect.*
val str: String = null
val exprString = Expr(str)
Expr(exprString.show)
}
}
2 changes: 2 additions & 0 deletions tests/run-macros/i23008/Test_2.scala
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@@ -0,0 +1,2 @@
@main def Test =
println(Macros.buildString)
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