Add reflect asSeenFrom

Fixes #14957

Author: nicolasstucki

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

@@ -1774,6 +1774,8 @@ class QuotesImpl private (using val ctx: Context) extends Quotes, QuoteUnpickler
         def typeArgs: List[TypeRepr] = self match
           case AppliedType(_, args) => args
           case _ => List.empty
+        def asSeenFrom(pre: TypeRepr, cls: Symbol): TypeRepr =
+          self.asSeenFrom(pre, cls)
       end extension
     end TypeReprMethods
 

library/src/scala/quoted/Quotes.scala

@@ -2684,6 +2684,13 @@ trait Quotes { self: runtime.QuoteUnpickler & runtime.QuoteMatching =>
 
         /** The applied type arguments (empty if there is no such arguments) */
         def typeArgs: List[TypeRepr]
+
+        /** This type seen as if it were the type of a member of prefix type `pre`
+         *  declared in class `cls`.
+         */
+        @experimental
+        def asSeenFrom(pre: TypeRepr, cls: Symbol): TypeRepr
+
       end extension
     }
 

tests/run-macros/i14957.check

@@ -0,0 +1 @@
+ => D[scala.Int]

tests/run-macros/i14957/Macro_1.scala

@@ -0,0 +1,20 @@
+import scala.quoted.*
+
+inline def asSeenFromTest: String = ${ impl }
+
+private def impl(using Quotes): Expr[String] =
+  import quotes.reflect.*
+  val aSym = Symbol.requiredClass("A")
+  val xSym = aSym.methodMember("x").head
+  // =>D[B] as seen from C with owner A
+  Expr(xSym.info.asSeenFrom(TypeRepr.of[C], aSym).show)
+
+
+trait D[E]
+
+class A[B] {
+  def x: D[B] = ???
+}
+
+class C extends A[Int]:
+  override def x: D[Int] = ???

tests/run-macros/i14957/Test_2.scala

@@ -0,0 +1,3 @@
+@main
+def Test: Unit =
+  println(asSeenFromTest)