Allow nested Quotes with a different owners

This makes it possible to create `Expr`s with different owners to avoid
a call to `changeOwner`.

Author: nicolasstucki

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

@@ -2617,6 +2617,8 @@ class QuotesImpl private (using val ctx: Context) extends Quotes, QuoteUnpickler
 
         def show(using printer: Printer[Symbol]): String = printer.show(self)
 
+        def asQuotes: Nested = new QuotesImpl(using ctx.withOwner(self))
+
       end extension
 
       private def appliedTypeRef(sym: Symbol): TypeRepr =
@@ -2907,6 +2909,10 @@ class QuotesImpl private (using val ctx: Context) extends Quotes, QuoteUnpickler
                    |which has the AST representation
                    |${Printer.TreeStructure.show(tree)}
                    |
+                   |
+                   |
+                   |Tip: The owner of a tree can be changed using method `Tree.changeOwner`.
+                   |Tip: The default owner of definitions created in quotes can be changed using method `Symbol.asQuotes`.
                    |""".stripMargin)
             case _ => traverseChildren(t)
       }.traverse(tree)

library/src/scala/quoted/Quotes.scala

@@ -3774,6 +3774,27 @@ trait Quotes { self: runtime.QuoteUnpickler & runtime.QuoteMatching =>
 
         /** Case class or case object children of a sealed trait or cases of an `enum`. */
         def children: List[Symbol]
+
+        /** Returns a nested quote with this symbol as splice owner (`Symbol.spliceOwner`).
+         *
+         *  Changes the owner under which the definition in a quote are created.
+         *
+         *  Usage:
+         *  ```scala
+         *  new TreeMap:
+         *    override def transformTerm(tree: Term)(owner: Symbol): Term =
+         *      tree match
+         *        case tree: Ident =>
+         *          given Quotes = owner.asQuotes
+         *          // Definitions contained in the quote will be owned by `owner`.
+         *          // No need to use `changeOwner` in this case.
+         *          '{ val x = ???; x }.asTerm
+         *  ```
+         *  @syntax markdown
+         */
+        @experimental
+        def asQuotes: Nested
+
       end extension
     }
 

project/MiMaFilters.scala

@@ -4,5 +4,8 @@ import com.typesafe.tools.mima.core.ProblemFilters._
 
 object MiMaFilters {
   val Library: Seq[ProblemFilter] = Seq(
+    // New APIs that will be introduced in 3.2.0
+    exclude[ReversedMissingMethodProblem]("scala.quoted.Quotes#reflectModule#SymbolMethods.asQuotes"),
+    exclude[DirectMissingMethodProblem]("scala.quoted.Quotes#reflectModule#SymbolMethods.asQuotes"),
   )
 }

tests/pos-macros/i13571/Macro_1.scala

@@ -0,0 +1,20 @@
+import scala.quoted.*
+
+inline def checked2[A](inline n: A): A =
+  ${ checkedImpl2[A]('{n}) }
+
+private def checkedImpl2[A](n: Expr[A])(using Quotes, Type[A]): Expr[A] =
+  import quotes.reflect.*
+  val tree: Term = n.asTerm
+  val acc = new TreeMap:
+    override def transformTerm(tree: Term)(owner: Symbol): Term =
+      tree match
+        case Apply(Select(x, "*"), List(y)) =>
+          given Quotes = owner.asQuotes
+          '{
+            val xt = ${x.asExprOf[Long]}
+            xt
+          }.asTerm
+        case _ =>
+          super.transformTerm(tree)(owner)
+  acc.transformTerm(tree)(Symbol.spliceOwner).asExprOf[A]

tests/pos-macros/i13571/Test_2.scala

@@ -0,0 +1,6 @@
+  def test = {
+    val u = 3L
+    checked2(List(1L, 2L).map { k =>
+       u * 2L
+     })
+  }

tests/pos-macros/i13571b/Macro_1.scala

@@ -0,0 +1,22 @@
+import scala.quoted.*
+
+inline def checked2[A](inline n: A): A =
+  ${ checkedImpl2[A]('{n}) }
+
+private def checkedImpl2[A](n: Expr[A])(using Quotes, Type[A]): Expr[A] =
+  import quotes.reflect.*
+  val tree: Term = n.asTerm
+  val acc = new TreeMap:
+    override def transformTerm(tree: Term)(owner: Symbol): Term =
+      tree match
+        case Apply(Select(x, "*"), List(y)) =>
+          bindLong(x.asExprOf[Long])(using owner.asQuotes).asTerm
+        case _ =>
+          super.transformTerm(tree)(owner)
+  acc.transformTerm(tree)(Symbol.spliceOwner).asExprOf[A]
+
+def bindLong(expr: Expr[Long])(using Quotes): Expr[Long] =
+  '{
+    val xt = $expr
+    xt
+  }

tests/pos-macros/i13571b/Test_2.scala

@@ -0,0 +1,6 @@
+  def test = {
+    val u = 3L
+    checked2(List(1L, 2L).map { k =>
+       u * 2L
+     })
+  }