Add reflect TypeLambda.declaredVariances

Fixes #16734

Author: nicolasstucki

compiler/src/scala/quoted/runtime/impl/QuotesImpl.scala

@@ -2212,6 +2212,9 @@ class QuotesImpl private (using val ctx: Context) extends Quotes, QuoteUnpickler
       extension (self: TypeLambda)
         def param(idx: Int): TypeRepr = self.newParamRef(idx)
         def paramBounds: List[TypeBounds] = self.paramInfos
+        def declaredVariances: List[Flags] =
+          if self.isDeclaredVarianceLambda then self.declaredVariances
+          else self.paramNames.map(_ => Flags.EmptyFlags)
       end extension
     end TypeLambdaMethods
 

library/src/scala/quoted/Quotes.scala

@@ -3235,8 +3235,16 @@ trait Quotes { self: runtime.QuoteUnpickler & runtime.QuoteMatching =>
     /** Extension methods of `TypeLambda` */
     trait TypeLambdaMethods:
       extension (self: TypeLambda)
+        /** Reference to the i-th parameter */
+        /** Type bounds of the i-th parameter */
         def param(idx: Int) : TypeRepr
         def paramBounds: List[TypeBounds]
+        /** Variance flags for the i-th parameter
+         *
+         *  Variance flags can be one of `Flags.{Covariant, Contravariant, EmptyFlags}`.
+         */
+        @experimental
+        def declaredVariances: List[Flags]
       end extension
     end TypeLambdaMethods
 

tests/run-custom-args/tasty-inspector/stdlibExperimentalDefinitions.scala

@@ -66,6 +66,7 @@ val experimentalDefinitionInLibrary = Set(
   // Should be stabilized in 3.4.0
   "scala.quoted.Quotes.reflectModule.defnModule.FunctionClass",
   "scala.quoted.Quotes.reflectModule.FlagsModule.AbsOverride",
+  "scala.quoted.Quotes.reflectModule.TypeLambdaMethods.declaredVariances",
   // Can be stabilized in 3.4.0 (unsure) or later
   "scala.quoted.Quotes.reflectModule.CompilationInfoModule.XmacroSettings",
   "scala.quoted.Quotes.reflectModule.FlagsModule.JavaAnnotation",

tests/run-macros/i16734.check

@@ -0,0 +1,55 @@
+trait K1Inv
+F
+A
+
+trait K1Cov
+F
++A
+
+trait K1Con
+F
+-A
+
+trait K2InvInv
+F
+A, B
+
+trait K2InvCov
+F
+A, +B
+
+trait K2InvCon
+F
+A, -B
+
+trait K2CovInv
+F
++A, B
+
+trait K2CovCov
+F
++A, +B
+
+trait K2CovCon
+F
++A, -B
+
+trait K2ConInv
+F
+-A, B
+
+trait K2ConCov
+F
+-A, +B
+
+trait K2ConCon
+F
+-A, -B
+
+trait KFunky
+G
+A, +B, -C, D, +E, -F
+X1, +Y1, -Z1
+X2, +Y2, -Z2
+X3, +Y3, -Z3
+

tests/run-macros/i16734/Macro_1.scala

@@ -0,0 +1,21 @@
+import scala.quoted.*
+
+inline def variances[A <: AnyKind]: String =
+  ${variancesImpl[A]}
+
+def variancesImpl[A <: AnyKind: Type](using Quotes): Expr[String] =
+  import quotes.reflect.*
+  def loop(tpe: TypeRepr): List[String] =
+    tpe match
+      case tpe: TypeLambda =>
+        tpe.paramNames.zip(tpe.declaredVariances).map { (name, variance) =>
+          if variance == Flags.Covariant then "+" + name
+          else if variance == Flags.Contravariant then "-" + name
+          else name
+        }.mkString(", ") :: tpe.paramTypes.flatMap(loop)
+      case tpe: TypeBounds =>
+        loop(tpe.low) ++ loop(tpe.hi)
+      case _ =>
+        Nil
+  val res = (TypeRepr.of[A].typeSymbol :: loop(TypeRepr.of[A])).mkString("", "\n", "\n")
+  Expr(res)

tests/run-macros/i16734/Test_2.scala

@@ -0,0 +1,32 @@
+trait K1Inv[F[A]]
+trait K1Cov[F[+A]]
+trait K1Con[F[-A]]
+
+trait K2InvInv[F[A, B]]
+trait K2InvCov[F[A, +B]]
+trait K2InvCon[F[A, -B]]
+trait K2CovInv[F[+A, B]]
+trait K2CovCov[F[+A, +B]]
+trait K2CovCon[F[+A, -B]]
+trait K2ConInv[F[-A, B]]
+trait K2ConCov[F[-A, +B]]
+trait K2ConCon[F[-A, -B]]
+
+
+trait KFunky[G[A, +B, -C, D[X1, +Y1, -Z1], +E[X2, +Y2, -Z2], -F[X3, +Y3, -Z3]]]
+
+
+@main def Test =
+  println(variances[K1Inv])
+  println(variances[K1Cov])
+  println(variances[K1Con])
+  println(variances[K2InvInv])
+  println(variances[K2InvCov])
+  println(variances[K2InvCon])
+  println(variances[K2CovInv])
+  println(variances[K2CovCov])
+  println(variances[K2CovCon])
+  println(variances[K2ConInv])
+  println(variances[K2ConCov])
+  println(variances[K2ConCon])
+  println(variances[KFunky])