Provide more efficient implemetation of Block.let

Author: nicolasstucki

compiler/src/dotty/tools/dotc/quoted/QuoteContextImpl.scala

@@ -706,6 +706,15 @@ class QuoteContextImpl private (ctx: Context) extends QuoteContext:
         tpd.cpy.Block(original)(stats, expr)
       def unapply(x: Block): Option[(List[Statement], Term)] =
         Some((x.statements, x.expr))
+
+      def let(rhs: Term)(body: Ident => Term): Term =
+        let(List(rhs))(x => body(x.head))
+
+      def let(terms: List[Term])(body: List[Ident] => Term): Term =
+        val vdefs = terms.map(term => tpd.SyntheticValDef("x".toTermName, term))
+        val refs = vdefs.map(vdef => tpd.ref(vdef.symbol).asInstanceOf[Ident])
+        Block(vdefs, body(refs))
+
     end Block
 
     object BlockMethodsImpl extends BlockMethods:

library/src/scala/tasty/Reflection.scala

@@ -819,20 +819,10 @@ trait Reflection { reflection =>
     def apply(stats: List[Statement], expr: Term): Block
 
     /** Creates a block `{ val x = <rhs: Term>; <body(x): Term> }` */
-    def let(rhs: Term)(body: Ident => Term): Term = {
-      val sym = Symbol.newVal(Symbol.currentOwner, "x", rhs.tpe.widen, Flags.EmptyFlags, Symbol.noSymbol)
-      Block(List(ValDef(sym, Some(rhs))), body(Ref(sym).asInstanceOf[Ident]))
-    }
+    def let(rhs: Term)(body: Ident => Term): Term
 
     /** Creates a block `{ val x1 = <terms(0): Term>; ...; val xn = <terms(n-1): Term>; <body(List(x1, ..., xn)): Term> }` */
-    def let(terms: List[Term])(body: List[Ident] => Term): Term = {
-      // TODO implement efficitent flat version
-      def rec(xs: List[Term], acc: List[Ident]): Term = xs match {
-        case Nil => body(acc)
-        case x :: xs => let(x) { (x: Ident) => rec(xs, x :: acc) }
-      }
-      rec(terms, Nil)
-    }
+    def let(terms: List[Term])(body: List[Ident] => Term): Term
 
     def copy(original: Tree)(stats: List[Statement], expr: Term): Block