Reused bindings in staged code

[liufengyun]

Run on scastie: https://scastie.scala-lang.org/aIv0YMfSSoCH5tuen4bUKg

minimized code

import scala.quoted._
import scala.quoted.staging._

def foo(n: Int, t: Expr[Int])(given QuoteContext): Expr[Int] =
  if (n == 0) t
  else '{ val a = ${Expr(n)}; ${foo(n - 1, 'a)} + $t  }

@main def main = {
  // make available the necessary toolbox for runtime code generation
  given Toolbox = Toolbox.make(getClass.getClassLoader)

  val f: Int = run { foo(2, Expr(5)) }

  println(f)
}

Crash output (click arrow to expand)

class dotty.tools.dotc.reporting.diagnostic.messages$Error at /tmp/scastie2283433749370612327/src/main/scala/main.scala:<162..184>: undefined: [cannot display due to dotty.tools.dotc.core.Symbols$NoSymbol$ cannot be cast to dotty.tools.dotc.core.Symbols$ClassSymbol, raw string = Select(Inlined(EmptyTree,List(),Ident(a)),+)] # 14345: TermRef(TermRef(NoPrefix,val a),+) at quotedFrontend

class dotty.tools.dotc.reporting.diagnostic.messages$Error at /tmp/scastie2283433749370612327/src/main/scala/main.scala:<162..184>: undefined: [cannot display due to dotty.tools.dotc.core.Symbols$NoSymbol$ cannot be cast to dotty.tools.dotc.core.Symbols$ClassSymbol, raw string = Select(Inlined(EmptyTree,List(),Ident(a)),+)] # 14345: TermRef(TermRef(NoPrefix,val a),+) at quotedFrontend
	at dotty.tools.dotc.reporting.Reporting.error(Reporter.scala:135)
	at dotty.tools.dotc.core.Contexts$Context.error(Contexts.scala:75)
	at dotty.tools.dotc.typer.ErrorReporting$.errorType(ErrorReporting.scala:29)
	at dotty.tools.dotc.typer.TypeAssigner.assignType(TypeAssigner.scala:414)
	at dotty.tools.dotc.typer.Typer.assignType(Typer.scala:83)
	at dotty.tools.dotc.ast.tpd$.Apply(tpd.scala:46)
	at dotty.tools.dotc.core.tasty.TreeUnpickler$TreeReader.readLengthTerm$1(TreeUnpickler.scala:1091)
	at dotty.tools.dotc.core.tasty.TreeUnpickler$TreeReader.readTerm(TreeUnpickler.scala:1212)
	at dotty.tools.dotc.core.tasty.TreeUnpickler$TreeReader.readLengthTerm$1(TreeUnpickler.scala:1104)
	at dotty.tools.dotc.core.tasty.TreeUnpickler$TreeReader.readTerm(TreeUnpickler.scala:1212)
	at dotty.tools.dotc.core.tasty.TreeUnpickler$TreeReader.readLengthTerm$1(TreeUnpickler.scala:1115)
	at dotty.tools.dotc.core.tasty.TreeUnpickler$TreeReader.readTerm(TreeUnpickler.scala:1212)
	at dotty.tools.dotc.core.tasty.TreeUnpickler.unpickle(TreeUnpickler.scala:107)
	at dotty.tools.dotc.core.tasty.DottyUnpickler.computeRootTrees(DottyUnpickler.scala:59)
	at dotty.tools.dotc.ast.tpd$TreeProvider.rootTrees(tpd.scala:1107)
	at dotty.tools.dotc.core.tasty.DottyUnpickler.rootTrees(DottyUnpickler.scala:41)
	at dotty.tools.dotc.ast.tpd$TreeProvider.tree(tpd.scala:1111)
	at dotty.tools.dotc.core.tasty.DottyUnpickler.tree(DottyUnpickler.scala:41)
	at dotty.tools.dotc.core.quoted.PickledQuotes$.unpickle(PickledQuotes.scala:131)
	at dotty.tools.dotc.core.quoted.PickledQuotes$.unpickleExpr(PickledQuotes.scala:66)
	at dotty.tools.dotc.tastyreflect.ReflectionCompilerInterface.unpickleExpr(ReflectionCompilerInterface.scala:38)
	at scala.runtime.quoted.Unpickler$.unpickleExpr$direct(Unpickler.scala:16)
	at main$package$.foo(main.scala:6)
	at main$package$.foo$$anonfun$5$2$$anonfun$1(main.scala:6)
	at dotty.tools.dotc.core.tasty.TreeUnpickler$TreeReader.readHole(TreeUnpickler.scala:1293)
	at dotty.tools.dotc.core.tasty.TreeUnpickler$TreeReader.readLengthTerm$1(TreeUnpickler.scala:1204)
	at dotty.tools.dotc.core.tasty.TreeUnpickler$TreeReader.readTerm(TreeUnpickler.scala:1212)
	at dotty.tools.dotc.core.tasty.TreeUnpickler$TreeReader.readLengthTerm$1(TreeUnpickler.scala:1115)
	at dotty.tools.dotc.core.tasty.TreeUnpickler$TreeReader.readTerm(TreeUnpickler.scala:1212)
	at dotty.tools.dotc.core.tasty.TreeUnpickler$TreeReader.completeSelect$1(TreeUnpickler.scala:1024)
	at dotty.tools.dotc.core.tasty.TreeUnpickler$TreeReader.readSimpleTerm$1(TreeUnpickler.scala:1058)
	at dotty.tools.dotc.core.tasty.TreeUnpickler$TreeReader.readTerm(TreeUnpickler.scala:1212)
	at dotty.tools.dotc.core.tasty.TreeUnpickler$TreeReader.readLengthTerm$1(TreeUnpickler.scala:1090)
	at dotty.tools.dotc.core.tasty.TreeUnpickler$TreeReader.readTerm(TreeUnpickler.scala:1212)
	at dotty.tools.dotc.core.tasty.TreeUnpickler$TreeReader.readLengthTerm$1(TreeUnpickler.scala:1104)
	at dotty.tools.dotc.core.tasty.TreeUnpickler$TreeReader.readTerm(TreeUnpickler.scala:1212)
	at dotty.tools.dotc.core.tasty.TreeUnpickler$TreeReader.readLengthTerm$1(TreeUnpickler.scala:1115)
	at dotty.tools.dotc.core.tasty.TreeUnpickler$TreeReader.readTerm(TreeUnpickler.scala:1212)
	at dotty.tools.dotc.core.tasty.TreeUnpickler$TreeReader.readTerm(TreeUnpickler.scala:1006)
	at dotty.tools.dotc.core.tasty.TreeUnpickler.unpickle(TreeUnpickler.scala:107)
	at dotty.tools.dotc.core.tasty.DottyUnpickler.computeRootTrees(DottyUnpickler.scala:59)
	at dotty.tools.dotc.ast.tpd$TreeProvider.rootTrees(tpd.scala:1107)
	at dotty.tools.dotc.core.tasty.DottyUnpickler.rootTrees(DottyUnpickler.scala:41)
	at dotty.tools.dotc.ast.tpd$TreeProvider.tree(tpd.scala:1111)
	at dotty.tools.dotc.core.tasty.DottyUnpickler.tree(DottyUnpickler.scala:41)
	at dotty.tools.dotc.core.quoted.PickledQuotes$.unpickle(PickledQuotes.scala:131)
	at dotty.tools.dotc.core.quoted.PickledQuotes$.unpickleExpr(PickledQuotes.scala:66)
	at dotty.tools.dotc.tastyreflect.ReflectionCompilerInterface.unpickleExpr(ReflectionCompilerInterface.scala:38)
	at scala.runtime.quoted.Unpickler$.unpickleExpr$direct(Unpickler.scala:16)
	at main$package$.foo(main.scala:6)
	at main$package$.$anonfun$1(main.scala:12)
	at scala.quoted.staging.package$.run$$anonfun$1(staging.scala:19)
	at scala.quoted.staging.QuoteCompiler$QuotedFrontend.runOn$$anonfun$1(QuoteCompiler.scala:71)
	at scala.collection.immutable.List.flatMap(List.scala:265)
	at scala.quoted.staging.QuoteCompiler$QuotedFrontend.runOn(QuoteCompiler.scala:84)
	at dotty.tools.dotc.Run.runPhases$4$$anonfun$4(Run.scala:161)
	at dotty.runtime.function.JProcedure1.apply(JProcedure1.java:15)
	at dotty.runtime.function.JProcedure1.apply(JProcedure1.java:10)
	at scala.collection.ArrayOps$.foreach$extension(ArrayOps.scala:1323)
	at dotty.tools.dotc.Run.runPhases$5(Run.scala:171)
	at dotty.tools.dotc.Run.compileUnits$$anonfun$1(Run.scala:179)
	at dotty.runtime.function.JFunction0$mcV$sp.apply(JFunction0$mcV$sp.java:12)
	at dotty.tools.dotc.util.Stats$.maybeMonitored(Stats.scala:65)
	at dotty.tools.dotc.Run.compileUnits(Run.scala:186)
	at dotty.tools.dotc.Run.compileUnits(Run.scala:128)
	at scala.quoted.staging.QuoteCompiler$ExprRun.compileExpr(QuoteCompiler.scala:104)
	at scala.quoted.staging.QuoteDriver.run(QuoteDriver.scala:37)
	at scala.quoted.staging.Toolbox$$anon$1.run(Toolbox.scala:36)
	at scala.quoted.staging.package$.run(staging.scala:19)
	at main$package$.main(main.scala:12)
	at main.main(main.scala:8)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:498)
	at sbt.Run.invokeMain(Run.scala:115)
	at sbt.Run.execute$1(Run.scala:79)
	at sbt.Run.$anonfun$runWithLoader$4(Run.scala:92)
	at scala.runtime.java8.JFunction0$mcV$sp.apply(JFunction0$mcV$sp.java:23)
	at sbt.util.InterfaceUtil$$anon$1.get(InterfaceUtil.scala:10)
	at sbt.TrapExit$App.run(TrapExit.scala:257)
	at java.lang.Thread.run(Thread.java:748)