Do not approximate prefixes when using memberType in reflect API

Author: jchyb

Diff for: compiler/src/dotty/tools/dotc/core/TypeOps.scala

@@ -31,7 +31,7 @@ object TypeOps:
   /** The type `tp` as seen from prefix `pre` and owner `cls`. See the spec
    *  for what this means.
    */
-  final def asSeenFrom(tp: Type, pre: Type, cls: Symbol)(using Context): Type = {
+  final def asSeenFrom(tp: Type, pre: Type, cls: Symbol, approximateUnstablePrefixes: Boolean)(using Context): Type = {
     pre match {
       case pre: QualSkolemType =>
         // When a selection has an unstable qualifier, the qualifier type gets
@@ -42,7 +42,7 @@ object TypeOps:
         // compute the type as seen from the widened prefix, and in the rare
         // cases where this leads to an approximated type we recompute it with
         // the skolemized prefix. See the i6199* tests for usecases.
-        val widenedAsf = new AsSeenFromMap(pre.info, cls)
+        val widenedAsf = new AsSeenFromMap(pre.info, cls, approximateUnstablePrefixes)
         val ret = widenedAsf.apply(tp)
 
         if widenedAsf.approxCount == 0 then
@@ -52,11 +52,11 @@ object TypeOps:
       case _ =>
     }
 
-    new AsSeenFromMap(pre, cls).apply(tp)
+    new AsSeenFromMap(pre, cls, approximateUnstablePrefixes).apply(tp)
   }
 
   /** The TypeMap handling the asSeenFrom */
-  class AsSeenFromMap(pre: Type, cls: Symbol)(using Context) extends ApproximatingTypeMap, IdempotentCaptRefMap {
+  class AsSeenFromMap(pre: Type, cls: Symbol, approximateUnstablePrefixes: Boolean)(using Context) extends ApproximatingTypeMap, IdempotentCaptRefMap {
 
     /** The number of range approximations in invariant or contravariant positions
      *  performed by this TypeMap.
@@ -81,7 +81,7 @@ object TypeOps:
           case pre: SuperType => toPrefix(pre.thistpe, cls, thiscls)
           case _ =>
             if (thiscls.derivesFrom(cls) && pre.baseType(thiscls).exists)
-              if (variance <= 0 && !isLegalPrefix(pre))
+              if (approximateUnstablePrefixes && variance <= 0 && !isLegalPrefix(pre))
                 approxCount += 1
                 range(defn.NothingType, pre)
               else pre

Diff for: compiler/src/dotty/tools/dotc/core/Types.scala

@@ -1106,11 +1106,14 @@ object Types extends TypeUtils {
 
     /** This type seen as if it were the type of a member of prefix type `pre`
      *  declared in class `cls`.
+     *
+     * @param approximateUnstablePrefixes - needed for mamberType method in quotes reflect API,
+     * where we want to approximate less
      */
-    final def asSeenFrom(pre: Type, cls: Symbol)(using Context): Type = {
+    final def asSeenFrom(pre: Type, cls: Symbol, approximateUnstablePrefixes: Boolean = true)(using Context): Type = {
       record("asSeenFrom")
       if (!cls.membersNeedAsSeenFrom(pre)) this
-      else TypeOps.asSeenFrom(this, pre, cls)
+      else TypeOps.asSeenFrom(this, pre, cls, approximateUnstablePrefixes)
     }
 
 // ----- Subtype-related --------------------------------------------

Diff for: compiler/src/scala/quoted/runtime/impl/QuotesImpl.scala

@@ -1826,7 +1826,7 @@ class QuotesImpl private (using val ctx: Context) extends Quotes, QuoteUnpickler
         def termSymbol: Symbol = self.termSymbol
         def isSingleton: Boolean = self.isSingleton
         def memberType(member: Symbol): TypeRepr =
-          member.info.asSeenFrom(self, member.owner)
+          member.info.asSeenFrom(self, member.owner, approximateUnstablePrefixes = false)
         def baseClasses: List[Symbol] = self.baseClasses
         def baseType(cls: Symbol): TypeRepr = self.baseType(cls)
         def derivesFrom(cls: Symbol): Boolean = self.derivesFrom(cls)

Diff for: tests/pos-macros/i22424/Macro_1.scala

@@ -0,0 +1,25 @@
+
+import scala.quoted.*
+
+object MockMaker:
+  inline def inlineMock[T]: Unit = ${instance[T]}
+  transparent inline def transparentInlineMock[T]: Unit = ${instance[T]}
+
+  def instance[T: Type](using quotes: Quotes): Expr[Unit] =
+    import quotes.reflect._
+    val tpe = TypeRepr.of[T]
+    val symbol = tpe.typeSymbol.methodMember("innerTraitInOptions").head
+    tpe.memberType(symbol) match
+      case mt @ MethodType(_, args, _) =>
+        assert(args.head.typeSymbol != TypeRepr.of[Nothing].typeSymbol, "argument is incorrectly approximated")
+        val shownType = mt.show
+        val expectedType = "(x: m.Embedded#ATrait[scala.Predef.String, scala.Int])m.Embedded#ATrait[scala.Predef.String, scala.Int]"
+        assert(shownType == expectedType, s"Incorrect type shown. Obtained: $shownType, Expected: $expectedType")
+    '{()}
+
+trait PolymorphicTrait {
+  trait Embedded {
+    trait ATrait[A, B]
+    def innerTraitInOptions(x: ATrait[String, Int]): ATrait[String, Int]
+  }
+}

Diff for: tests/pos-macros/i22424/Test_2.scala

@@ -0,0 +1,4 @@
+@main def Test =
+  val m = new PolymorphicTrait {}
+  MockMaker.inlineMock[m.Embedded]
+  MockMaker.transparentInlineMock[m.Embedded]