Add reflect TypeLambda.paramVariances (#17568)

Fixes #16734

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

@@ -2246,6 +2246,8 @@ 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 paramVariances: List[Flags] =
+          self.typeParams.map(_.paramVariance)
       end extension
     end TypeLambdaMethods
 
@@ -2754,6 +2756,7 @@ class QuotesImpl private (using val ctx: Context) extends Quotes, QuoteUnpickler
           }
 
         def isTypeParam: Boolean = self.isTypeParam
+        def paramVariance: Flags = self.paramVariance
         def signature: Signature = self.signature
         def moduleClass: Symbol = self.denot.moduleClass
         def companionClass: Symbol = self.denot.companionClass

library/src/scala/quoted/Quotes.scala

@@ -3258,8 +3258,16 @@ trait Quotes { self: runtime.QuoteUnpickler & runtime.QuoteMatching =>
     /** Extension methods of `TypeLambda` */
     trait TypeLambdaMethods:
       extension (self: TypeLambda)
+        /** Reference to the i-th parameter */
         def param(idx: Int) : TypeRepr
+        /** Type bounds of the i-th parameter */
         def paramBounds: List[TypeBounds]
+        /** Variance flags for the i-th parameter
+         *
+         *  Variance flags can be one of `Flags.{Covariant, Contravariant, EmptyFlags}`.
+         */
+        @experimental
+        def paramVariances: List[Flags]
       end extension
     end TypeLambdaMethods
 
@@ -4078,8 +4086,17 @@ trait Quotes { self: runtime.QuoteUnpickler & runtime.QuoteMatching =>
         /** Fields of a case class type -- only the ones declared in primary constructor */
         def caseFields: List[Symbol]
 
+        /** Is this the symbol of a type parameter */
         def isTypeParam: Boolean
 
+        /** Variance flags for of this type parameter.
+         *
+         *  Variance flags can be one of `Flags.{Covariant, Contravariant, EmptyFlags}`.
+         *  If this is not the symbol of a type parameter the result is `Flags.EmptyFlags`.
+         */
+        @experimental
+        def paramVariance: Flags
+
         /** Signature of this definition */
         def signature: Signature
 

tests/run-macros/i16734a.check

@@ -0,0 +1,67 @@
+[F >: scala.Nothing <: [A >: scala.Nothing <: scala.Any] =>> scala.Any] =>> K1Inv[F]
+F
+A
+
+[F >: scala.Nothing <: [A >: scala.Nothing <: scala.Any] =>> scala.Any] =>> K1Cov[F]
+F
++A
+
+[F >: scala.Nothing <: [A >: scala.Nothing <: scala.Any] =>> scala.Any] =>> K1Con[F]
+F
+-A
+
+[F >: scala.Nothing <: [A >: scala.Nothing <: scala.Any, B >: scala.Nothing <: scala.Any] =>> scala.Any] =>> K2InvInv[F]
+F
+A, B
+
+[F >: scala.Nothing <: [A >: scala.Nothing <: scala.Any, B >: scala.Nothing <: scala.Any] =>> scala.Any] =>> K2InvCov[F]
+F
+A, +B
+
+[F >: scala.Nothing <: [A >: scala.Nothing <: scala.Any, B >: scala.Nothing <: scala.Any] =>> scala.Any] =>> K2InvCon[F]
+F
+A, -B
+
+[F >: scala.Nothing <: [A >: scala.Nothing <: scala.Any, B >: scala.Nothing <: scala.Any] =>> scala.Any] =>> K2CovInv[F]
+F
++A, B
+
+[F >: scala.Nothing <: [A >: scala.Nothing <: scala.Any, B >: scala.Nothing <: scala.Any] =>> scala.Any] =>> K2CovCov[F]
+F
++A, +B
+
+[F >: scala.Nothing <: [A >: scala.Nothing <: scala.Any, B >: scala.Nothing <: scala.Any] =>> scala.Any] =>> K2CovCon[F]
+F
++A, -B
+
+[F >: scala.Nothing <: [A >: scala.Nothing <: scala.Any, B >: scala.Nothing <: scala.Any] =>> scala.Any] =>> K2ConInv[F]
+F
+-A, B
+
+[F >: scala.Nothing <: [A >: scala.Nothing <: scala.Any, B >: scala.Nothing <: scala.Any] =>> scala.Any] =>> K2ConCov[F]
+F
+-A, +B
+
+[F >: scala.Nothing <: [A >: scala.Nothing <: scala.Any, B >: scala.Nothing <: scala.Any] =>> scala.Any] =>> K2ConCon[F]
+F
+-A, -B
+
+[G >: scala.Nothing <: [A >: scala.Nothing <: scala.Any, B >: scala.Nothing <: scala.Any, C >: scala.Nothing <: scala.Any, D >: scala.Nothing <: [X1 >: scala.Nothing <: scala.Any, Y1 >: scala.Nothing <: scala.Any, Z1 >: scala.Nothing <: scala.Any] =>> scala.Any, E >: scala.Nothing <: [X2 >: scala.Nothing <: scala.Any, Y2 >: scala.Nothing <: scala.Any, Z2 >: scala.Nothing <: scala.Any] =>> scala.Any, F >: scala.Nothing <: [X3 >: scala.Nothing <: scala.Any, Y3 >: scala.Nothing <: scala.Any, Z3 >: scala.Nothing <: scala.Any] =>> scala.Any] =>> scala.Any] =>> KFunky[G]
+G
+A, +B, -C, D, +E, -F
+X1, +Y1, -Z1
+X2, +Y2, -Z2
+X3, +Y3, -Z3
+
+[A >: scala.Nothing <: scala.Any, F >: scala.Nothing <: [B >: scala.Nothing <: scala.Any] =>> scala.Any] =>> F[A]
+A, +F
+B
+
+[A >: scala.Nothing <: scala.Any, F >: scala.Nothing <: [B >: scala.Nothing <: scala.Any] =>> scala.Any] =>> F[A]
++A, +F
++B
+
+[A >: scala.Nothing <: scala.Any, F >: scala.Nothing <: [B >: scala.Nothing <: scala.Any] =>> scala.Any] =>> F[A]
+-A, +F
+-B
+

tests/run-macros/i16734a/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.paramVariances).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 = (Type.show[A] :: loop(TypeRepr.of[A])).mkString("", "\n", "\n")
+  Expr(res)

tests/run-macros/i16734a/Test_2.scala

@@ -0,0 +1,34 @@
+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])
+  println(variances[[A, F[B]] =>> F[A]])
+  println(variances[[A, F[+B]] =>> F[A]])
+  println(variances[[A, F[-B]] =>> F[A]])

tests/run-macros/i16734b.check

@@ -0,0 +1,36 @@
+type F1Inv
+A
+
+type F1Cov
++A
+
+type F1Con
+-A
+
+type F2InvInv
+A, B
+
+type F2InvCov
+A, +B
+
+type F2InvCon
+A, -B
+
+type F2CovInv
++A, B
+
+type F2CovCov
++A, +B
+
+type F2CovCon
++A, -B
+
+type F2ConInv
+-A, B
+
+type F2ConCov
+-A, +B
+
+type F2ConCon
+-A, -B
+

tests/run-macros/i16734b/Macro_1.scala

@@ -0,0 +1,14 @@
+import scala.quoted.*
+
+inline def typeVariances[A <: AnyKind]: String =
+  ${variancesImpl[A]}
+
+def variancesImpl[A <: AnyKind: Type](using Quotes): Expr[String] =
+  import quotes.reflect.*
+  val TypeBounds(_, tl: TypeLambda) = TypeRepr.of[A].typeSymbol.info: @unchecked
+  val variances = tl.paramNames.zip(tl.paramVariances).map { (name, variance) =>
+    if variance == Flags.Covariant then "+" + name
+    else if variance == Flags.Contravariant then "-" + name
+    else name
+  }.mkString(", ")
+  Expr(TypeRepr.of[A].typeSymbol.toString() + "\n" + variances + "\n")

tests/run-macros/i16734b/Test_2.scala

@@ -0,0 +1,27 @@
+type F1Inv[A]
+type F1Cov[+A]
+type F1Con[-A]
+
+type F2InvInv[A, B]
+type F2InvCov[A, +B]
+type F2InvCon[A, -B]
+type F2CovInv[+A, B]
+type F2CovCov[+A, +B]
+type F2CovCon[+A, -B]
+type F2ConInv[-A, B]
+type F2ConCov[-A, +B]
+type F2ConCon[-A, -B]
+
+@main def Test =
+  println(typeVariances[F1Inv])
+  println(typeVariances[F1Cov])
+  println(typeVariances[F1Con])
+  println(typeVariances[F2InvInv])
+  println(typeVariances[F2InvCov])
+  println(typeVariances[F2InvCon])
+  println(typeVariances[F2CovInv])
+  println(typeVariances[F2CovCov])
+  println(typeVariances[F2CovCon])
+  println(typeVariances[F2ConInv])
+  println(typeVariances[F2ConCov])
+  println(typeVariances[F2ConCon])

tests/run-macros/i16734c.check

@@ -0,0 +1,36 @@
+class C1Inv
+A
+
+class C1Cov
++A
+
+class C1Con
+-A
+
+class C2InvInv
+A, B
+
+class C2InvCov
+A, +B
+
+class C2InvCon
+A, -B
+
+class C2CovInv
++A, B
+
+class C2CovCov
++A, +B
+
+class C2CovCon
++A, -B
+
+class C2ConInv
+-A, B
+
+class C2ConCov
+-A, +B
+
+class C2ConCon
+-A, -B
+

tests/run-macros/i16734c/Macro_1.scala

@@ -0,0 +1,14 @@
+import scala.quoted.*
+
+inline def classVariances[A <: AnyKind]: String =
+  ${variancesImpl[A]}
+
+def variancesImpl[A <: AnyKind: Type](using Quotes): Expr[String] =
+  import quotes.reflect.*
+  val variances = TypeRepr.of[A].typeSymbol.typeMembers.filter(_.isTypeParam).map { sym =>
+    if sym.paramVariance == Flags.Covariant then "+" + sym.name
+    else if sym.paramVariance == Flags.Contravariant then "-" + sym.name
+    else sym.name
+  }
+  val res = variances.mkString(TypeRepr.of[A].typeSymbol.toString + "\n", ", ", "\n")
+  Expr(res)

tests/run-macros/i16734c/Test_2.scala

@@ -0,0 +1,27 @@
+class C1Inv[A] { type T }
+class C1Cov[+A] { type T }
+class C1Con[-A] { type T }
+
+class C2InvInv[A, B] { type T }
+class C2InvCov[A, +B] { type T }
+class C2InvCon[A, -B] { type T }
+class C2CovInv[+A, B] { type T }
+class C2CovCov[+A, +B] { type T }
+class C2CovCon[+A, -B] { type T }
+class C2ConInv[-A, B] { type T }
+class C2ConCov[-A, +B] { type T }
+class C2ConCon[-A, -B] { type T }
+
+@main def Test =
+  println(classVariances[C1Inv])
+  println(classVariances[C1Cov])
+  println(classVariances[C1Con])
+  println(classVariances[C2InvInv])
+  println(classVariances[C2InvCov])
+  println(classVariances[C2InvCon])
+  println(classVariances[C2CovInv])
+  println(classVariances[C2CovCov])
+  println(classVariances[C2CovCon])
+  println(classVariances[C2ConInv])
+  println(classVariances[C2ConCov])
+  println(classVariances[C2ConCon])

tests/run-tasty-inspector/stdlibExperimentalDefinitions.scala

@@ -68,6 +68,8 @@ val experimentalDefinitionInLibrary = Set(
   "scala.annotation.init$.region",
 
    //// New APIs: Quotes
+  "scala.quoted.Quotes.reflectModule.TypeLambdaMethods.paramVariances",
+  "scala.quoted.Quotes.reflectModule.SymbolMethods.paramVariance",
   // Can be stabilized in 3.4.0 (unsure) or later
   "scala.quoted.Quotes.reflectModule.CompilationInfoModule.XmacroSettings",
   "scala.quoted.Quotes.reflectModule.FlagsModule.JavaAnnotation",