Support custom val symbol in ValDef.let

Author: cchantep

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

@@ -305,6 +305,11 @@ class QuotesImpl private (using val ctx: Context) extends Quotes, QuoteUnpickler
         val vdefs = terms.map(term => tpd.SyntheticValDef("x".toTermName, term)(using ctx1))
         val refs = vdefs.map(vdef => tpd.ref(vdef.symbol).asInstanceOf[Ref])
         Block(vdefs, body(refs))
+
+      def let(owner: Symbol, symbol: Symbol, rhs: Term)(body: Ref => Term): Term =
+        val vdef = apply(symbol, Some(rhs)).changeOwner(owner)
+        val ref = tpd.ref(vdef.symbol).asInstanceOf[Ref]
+        Block(List(vdef), body(ref))
     end ValDef
 
     given ValDefMethods: ValDefMethods with

library/src/scala/quoted/Quotes.scala

@@ -607,6 +607,41 @@ trait Quotes { self: runtime.QuoteUnpickler & runtime.QuoteMatching =>
 
       /** Creates a block `{ val x1 = <terms(0): Term>; ...; val xn = <terms(n-1): Term>; <body(List(x1, ..., xn)): Term> }` */
       def let(owner: Symbol, terms: List[Term])(body: List[Ref] => Term): Term
+
+      /**
+       * Creates a block `{ val x = <rhs: Term>; <body(x): Term> }`
+       * with the given symbol for the `val` (allowing to specify `Flags`).
+       *
+       * Usage:
+       * ```scala sc:nocompile
+       * val tpe = TypeRepr.of[String]
+       * 
+       * val valSym = Symbol.newVal(
+       *   Symbol.spliceOwner,
+       *   "myValName",
+       *   tpe,
+       *   Flags.Lazy,
+       *   Symbol.noSymbol
+       * )
+       * 
+       * ValDef.let(Symbol.spliceOwner, valSym, Expr("foo")) { v =>
+       *   '{ println(v) }.asTerm
+       * }
+       * ```
+       *
+       * In this way, it's possible to create an `Ref` to the `val` 
+       * before its definition (required for recursive/lazy definitions).
+       * 
+       * ```scala sc:nocompile
+       * // After `tpe` and `valSym` but before `let` call
+       * val earlyRef = Typed(Ref(valSym), Inferred(tpe))
+       * ```
+       *
+       * @param symbol the `val` symbol
+       * @see `Symbol.newVal`
+       */
+      @experimental
+      def let(owner: Symbol, symbol: Symbol, rhs: Term)(body: Ref => Term): Term
     }
 
     /** Makes extension methods on `ValDef` available without any imports */

tests/run-macros/i13929.check

@@ -0,0 +1,2 @@
+early=i13929
+vref=i13929

tests/run-macros/i13929/Macro_1.scala

@@ -0,0 +1,26 @@
+import scala.quoted.*
+
+inline def testSymLet[T](f: T) = ${ testSymLetImpl[T]('f) }
+
+def testSymLetImpl[T: Type](f: Expr[T])(using Quotes): Expr[Unit] = {
+  import quotes.reflect.*
+
+  val tpe = TypeRepr.of[T]
+
+  val valSym = Symbol.newVal(
+    Symbol.spliceOwner,
+    "myVal",
+    tpe,
+    Flags.Lazy,
+    Symbol.noSymbol
+  )
+
+  val earlyRef = Typed(Ref(valSym), Inferred(tpe))
+
+  ValDef.let(Symbol.spliceOwner, valSym, f) { vref =>
+    '{
+      println("early=" + ${earlyRef.asExpr}.toString())
+      println("vref=" + ${vref.asExpr}.toString())
+    }.asTerm
+  }.asExprOf[Unit]
+}

tests/run-macros/i13929/Test_2.scala

@@ -0,0 +1 @@
+@main def Test = testSymLet("i13929")