Add reflect Symbol.paramVariance

Related to #16734

Author: nicolasstucki

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

@@ -2756,6 +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

@@ -4086,8 +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/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

@@ -69,6 +69,7 @@ val experimentalDefinitionInLibrary = Set(
 
    //// 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",