Add quoted ExprOps toExprOfSeq

The implementation of `toExprOfSeq` uses TASTy reflect to generate the most compact code possible.
It also gives an efficient way to splice varargs.

Author: nicolasstucki

compiler/src/dotty/tools/dotc/transform/SeqLiterals.scala

@@ -31,6 +31,6 @@ class SeqLiterals extends MiniPhase {
       val arr = JavaSeqLiteral(tree.elems, tree.elemtpt)
       //println(i"trans seq $tree, arr = $arr: ${arr.tpe} ${arr.tpe.elemType}")
       val elemtp = tree.elemtpt.tpe
-      wrapArray(arr, elemtp)
+      wrapArray(arr, elemtp).withSpan(tree.span)
   }
 }

library/src-bootstrapped/scala/quoted/package.scala

@@ -54,10 +54,34 @@ package object quoted {
   implicit object ExprOps {
     def (x: T) toExpr[T: Liftable] given QuoteContext: Expr[T] = the[Liftable[T]].toExpr(x)
 
-    def (list: List[Expr[T]]) toExprOfList[T: Type] given QuoteContext: Expr[List[T]] = list match {
-      case x :: xs  => '{ $x :: ${xs.toExprOfList} }
-      case Nil => '{ Nil }
+   /** Lifts this sequence of expressions into an expression of a sequence
+    *
+    *  Transforms a list of expression
+    *    `Seq(e1, e2, ...)` where `ei: Expr[T]`
+    *  to an expression equivalent to
+    *    `'{ Seq($e1, $e2, ...) }` typed as an `Expr[Seq[T]]`
+    *
+    *  Usage:
+    *  ```scala
+    *  '{ List(${List(1, 2, 3).toExprOfSeq}: _*) } // equvalent to '{ List(1, 2, 3) }
+    *  ```
+    */
+    def (seq: Seq[Expr[T]]) toExprOfSeq[T] given (tp: Type[T], qctx: QuoteContext): Expr[Seq[T]] = {
+      import qctx.tasty._
+      Repeated(seq.map(_.unseal).toList, tp.unseal).seal.asInstanceOf[Expr[Seq[T]]]
     }
+
+    /** Lifts this list of expressions into an expression of a list
+     *
+     *  Transforms a list of expression
+     *    `List(e1, e2, ...)` where `ei: Expr[T]`
+     *  to an expression equivalent to
+     *    `'{ List($e1, $e2, ...) }` typed as an `Expr[List[T]]`
+     */
+    def (list: List[Expr[T]]) toExprOfList[T] given Type[T], QuoteContext: Expr[List[T]] =
+      if (list.isEmpty) '{ Nil } else '{ List(${list.toExprOfSeq}: _*) }
+
+
   }
 
 }

tests/run-macros/i6765-b.check

@@ -1,8 +1,2 @@
-{
-  val x$3: java.lang.String = "One"
-  scala.Nil.::[java.lang.String](x$3)
-}
-{
-  val x$3: java.lang.String = "One"
-  scala.Nil.::[java.lang.String](x$3)
-}
+scala.List.apply[java.lang.String]("One": _*)
+scala.List.apply[java.lang.String]("One": _*)

tests/run-macros/i6765-c.check

@@ -0,0 +1,18 @@
+scala.Nil
+List()
+
+scala.List.apply[java.lang.String]("#0": _*)
+List(#0)
+
+scala.List.apply[java.lang.String]("#0", "#1": _*)
+List(#0, #1)
+
+scala.List.apply[java.lang.String]("#0", "#1", "#2": _*)
+List(#0, #1, #2)
+
+scala.List.apply[java.lang.String]("#0", "#1", "#2", "#3": _*)
+List(#0, #1, #2, #3)
+
+scala.List.apply[java.lang.String]("#0", "#1", "#2", "#3", "#4": _*)
+List(#0, #1, #2, #3, #4)
+

tests/run-macros/i6765-c/Macro_1.scala

@@ -0,0 +1,9 @@
+import scala.quoted._
+import delegate scala.quoted._
+
+inline def foo(inline n: Int) = ${fooImpl(n)}
+
+def fooImpl(n: Int) given (qctx: QuoteContext) = {
+  val res = List.tabulate(n)(i => ("#" + i).toExpr).toExprOfList
+  '{ ${res.show.toExpr} + "\n" + $res.toString + "\n" }
+}

tests/run-macros/i6765-c/Test_2.scala

@@ -0,0 +1,10 @@
+object Test {
+  def main(args: Array[String]): Unit = {
+    println(foo(0))
+    println(foo(1))
+    println(foo(2))
+    println(foo(3))
+    println(foo(4))
+    println(foo(5))
+  }
+}

tests/run-macros/i6765.check

@@ -1,8 +1,2 @@
-{
-  val x$3: java.lang.String = "One"
-  scala.Nil.::[java.lang.String](x$3)
-}
-{
-  val x$3: java.lang.String = "One"
-  scala.Nil.::[java.lang.String](x$3)
-}
+scala.List.apply[java.lang.String]("One": _*)
+scala.List.apply[java.lang.String]("One": _*)

tests/run-macros/quote-toExprOfSeq.check

@@ -0,0 +1,4 @@
+WrappedArray(1, 2, 3)
+WrappedArray(1, 2, 3)
+List(1, 2, 3)
+2

tests/run-macros/quote-toExprOfSeq/Macro_1.scala

@@ -0,0 +1,8 @@
+import scala.quoted._
+import delegate scala.quoted._
+
+inline def seq = ${fooImpl}
+
+def fooImpl given (qctx: QuoteContext) = {
+  List('{1}, '{2}, '{3}).toExprOfSeq
+}

tests/run-macros/quote-toExprOfSeq/Test_2.scala

@@ -0,0 +1,9 @@
+object Test {
+  def main(args: Array[String]): Unit = {
+    println(seq)
+    val s: Seq[Int] = seq
+    println(s)
+    println(List(seq: _*))
+    println(seq(1))
+  }
+}