Macro annotation that processes inlined tree crashes under `-Ycheck:all`

[pweisenburger]

Compiler version

3.3.1-RC1-bin-20230216-2507577-NIGHTLY

Minimized code

Consider the following macro definition (the macro annotation extracts the number v that is applied to locally in inlineMethod):

import scala.annotation.MacroAnnotation
import scala.quoted.*

class annotation extends MacroAnnotation:
  def transform(using Quotes)(tree: quotes.reflect.Definition) =
    import quotes.reflect.*

    tree match
      case tree: ClassDef =>
        val List(DefDef(name, paramss, tpt, Some(body))) = tree.body: @unchecked

        val rhs = body match
          case Inlined(_, _, Block(List(Apply(_ /* `locally` */, List(rhs))), _)) => rhs

        val method = DefDef.copy(tree.body.head)(name, paramss, tpt, Some(rhs.changeOwner(tree.body.head.symbol)))

        List(ClassDef.copy(tree)(tree.name, tree.constructor, tree.parents, tree.self, List(method)))

Macro call site:

transparent inline def inlineMethod(v: Int) =
  locally(v)
  0

@annotation
class Test:
  def method = inlineMethod(42)

Output

When compiling with -Ycheck:all, the compiler crashes; otherwise, the code compiles. It seems that the transparent inline method is crucial to produce the crash.

Error and Stack Trace

*** error while checking Test.scala after phase inlining ***
java.util.NoSuchElementException: head of empty list while running Ycheck on Test.scala
java.util.NoSuchElementException: head of empty list while compiling Test.scala, TestMacro.scala
[error] ## Exception when compiling 2 sources
[error] java.util.NoSuchElementException: head of empty list
[error] scala.collection.immutable.Nil$.head(List.scala:662)
[error] scala.collection.immutable.Nil$.head(List.scala:661)
[error] dotty.tools.dotc.transform.YCheckPositions$$anon$1.traverse(YCheckPositions.scala:45)
[error] dotty.tools.dotc.ast.Trees$Instance$TreeTraverser.apply(Trees.scala:1660)
[error] dotty.tools.dotc.ast.Trees$Instance$TreeTraverser.apply(Trees.scala:1660)
[error] dotty.tools.dotc.ast.Trees$Instance$TreeAccumulator.foldOver(Trees.scala:1620)
[error] dotty.tools.dotc.ast.Trees$Instance$TreeTraverser.traverseChildren(Trees.scala:1661)
[error] dotty.tools.dotc.transform.YCheckPositions$$anon$1.traverse(YCheckPositions.scala:53)
[error] dotty.tools.dotc.ast.Trees$Instance$TreeTraverser.apply(Trees.scala:1660)
[error] dotty.tools.dotc.ast.Trees$Instance$TreeTraverser.apply(Trees.scala:1660)
[error] dotty.tools.dotc.ast.Trees$Instance$TreeAccumulator.fold$1(Trees.scala:1532)
[error] dotty.tools.dotc.ast.Trees$Instance$TreeAccumulator.apply(Trees.scala:1534)
[error] dotty.tools.dotc.ast.Trees$Instance$TreeAccumulator.foldOver(Trees.scala:1627)
[error] dotty.tools.dotc.ast.Trees$Instance$TreeTraverser.traverseChildren(Trees.scala:1661)
[error] dotty.tools.dotc.transform.YCheckPositions$$anon$1.traverse(YCheckPositions.scala:53)
[error] dotty.tools.dotc.ast.Trees$Instance$TreeTraverser.apply(Trees.scala:1660)
[error] dotty.tools.dotc.ast.Trees$Instance$TreeTraverser.apply(Trees.scala:1660)
[error] dotty.tools.dotc.ast.Trees$Instance$TreeAccumulator.foldOver(Trees.scala:1624)
[error] dotty.tools.dotc.ast.Trees$Instance$TreeTraverser.traverseChildren(Trees.scala:1661)
[error] dotty.tools.dotc.transform.YCheckPositions$$anon$1.traverse(YCheckPositions.scala:53)
[error] dotty.tools.dotc.ast.Trees$Instance$TreeTraverser.apply(Trees.scala:1660)
[error] dotty.tools.dotc.ast.Trees$Instance$TreeTraverser.apply(Trees.scala:1660)
[error] dotty.tools.dotc.ast.Trees$Instance$TreeAccumulator.fold$1(Trees.scala:1532)
[error] dotty.tools.dotc.ast.Trees$Instance$TreeAccumulator.apply(Trees.scala:1534)
[error] dotty.tools.dotc.ast.Trees$Instance$TreeAccumulator.foldOver(Trees.scala:1633)
[error] dotty.tools.dotc.ast.Trees$Instance$TreeTraverser.traverseChildren(Trees.scala:1661)
[error] dotty.tools.dotc.transform.YCheckPositions$$anon$1.traverse(YCheckPositions.scala:53)
[error] dotty.tools.dotc.transform.YCheckPositions.checkPostCondition(YCheckPositions.scala:58)
[error] dotty.tools.dotc.transform.TreeChecker$Checker.typedUnadapted$$anonfun$1(TreeChecker.scala:412)
[error] scala.runtime.function.JProcedure1.apply(JProcedure1.java:15)
[error] scala.runtime.function.JProcedure1.apply(JProcedure1.java:10)
[error] scala.collection.immutable.List.foreach(List.scala:333)
[error] dotty.tools.dotc.transform.TreeChecker$Checker.typedUnadapted(TreeChecker.scala:412)
[error] dotty.tools.dotc.typer.Typer.typed(Typer.scala:3077)
[error] dotty.tools.dotc.typer.Typer.typed(Typer.scala:3081)
[error] dotty.tools.dotc.transform.TreeChecker$Checker.typed(TreeChecker.scala:378)
[error] dotty.tools.dotc.typer.Typer.typedExpr(Typer.scala:3193)
[error] dotty.tools.dotc.transform.TreeChecker.check(TreeChecker.scala:126)
[error] dotty.tools.dotc.transform.TreeChecker.run(TreeChecker.scala:106)
[error] dotty.tools.dotc.core.Phases$Phase.runOn$$anonfun$1(Phases.scala:324)
[error] scala.collection.immutable.List.map(List.scala:246)
[error] dotty.tools.dotc.core.Phases$Phase.runOn(Phases.scala:328)
[error] dotty.tools.dotc.Run.runPhases$1$$anonfun$1(Run.scala:247)
[error] scala.runtime.function.JProcedure1.apply(JProcedure1.java:15)
[error] scala.runtime.function.JProcedure1.apply(JProcedure1.java:10)
[error] scala.collection.ArrayOps$.foreach$extension(ArrayOps.scala:1321)
[error] dotty.tools.dotc.Run.runPhases$1(Run.scala:263)
[error] dotty.tools.dotc.Run.compileUnits$$anonfun$1(Run.scala:271)
[error] dotty.tools.dotc.Run.compileUnits$$anonfun$adapted$1(Run.scala:280)
[error] dotty.tools.dotc.util.Stats$.maybeMonitored(Stats.scala:67)
[error] dotty.tools.dotc.Run.compileUnits(Run.scala:280)
[error] dotty.tools.dotc.Run.compileUnits(Run.scala:201)
[error] dotty.tools.dotc.Driver.finish(Driver.scala:56)
[error] dotty.tools.dotc.Driver.doCompile(Driver.scala:36)
[error] dotty.tools.xsbt.CompilerBridgeDriver.run(CompilerBridgeDriver.java:88)
[error] dotty.tools.xsbt.CompilerBridge.run(CompilerBridge.java:22)

Note that I'm not entirely certain whether extracting a subtree of an Inlined node using Inlined(_, _, Block(List(Apply(_, List(rhs))), _)) is legal, but I think it should be (how else would you get the tree to process it further).

[nicolasstucki]

Note that I'm not entirely certain whether extracting a subtree of an Inlined node using Inlined(_, , Block(List(Apply(, List(rhs))), _)) is legal, but I think it should be (how else would you get the tree to process it further).

You should not drop the inlined nodes. These are used to keep track of the source file of a position. Maybe you should write:

val rhs = body match
  case Inlined(call, bindings, Block(List(Apply(_ /* `locally` */, List(rhs))), _)) => Inlined.copy(body)(call, bindings, rhs)

[Gedochao]

// A.scala
//> using options -Ycheck:all
import scala.annotation.MacroAnnotation
import scala.annotation.experimental
import scala.quoted.*

@experimental
class annotation extends MacroAnnotation:
  def transform(using Quotes)(tree: quotes.reflect.Definition) =
    import quotes.reflect.*

    tree match
      case tree: ClassDef =>
        val List(DefDef(name, paramss, tpt, Some(body))) = tree.body: @unchecked

        val rhs = body match
          case Inlined(_, _, Block(List(Apply(_ /* `locally` */, List(rhs))), _)) => rhs

        val method = DefDef.copy(tree.body.head)(name, paramss, tpt, Some(rhs.changeOwner(tree.body.head.symbol)))

        List(ClassDef.copy(tree)(tree.name, tree.constructor, tree.parents, tree.self, List(method)))

// B.scala
import scala.annotation.experimental

transparent inline def inlineMethod(v: Int) =
  locally(v)
  0

@annotation
@experimental
class Test:
  def method = inlineMethod(42)

still crashes with 3.3.5-RC2.
For Scala 3.6.4-RC1 fails with:

Compiling project (Scala 3.6.4-RC1, JVM (23))
checking /Users/pchabelski/IdeaProjects/scala-cli-tests-2/untitled/17007/A.scala after phase typer
checking /Users/pchabelski/IdeaProjects/scala-cli-tests-2/untitled/17007/B.scala after phase typer
checking /Users/pchabelski/IdeaProjects/scala-cli-tests-2/untitled/17007/A.scala after phase checkUnusedPostTyper
checking /Users/pchabelski/IdeaProjects/scala-cli-tests-2/untitled/17007/B.scala after phase checkUnusedPostTyper
checking /Users/pchabelski/IdeaProjects/scala-cli-tests-2/untitled/17007/A.scala after phase checkShadowing
checking /Users/pchabelski/IdeaProjects/scala-cli-tests-2/untitled/17007/B.scala after phase checkShadowing
checking /Users/pchabelski/IdeaProjects/scala-cli-tests-2/untitled/17007/A.scala after phase inlinedPositions
checking /Users/pchabelski/IdeaProjects/scala-cli-tests-2/untitled/17007/B.scala after phase inlinedPositions
checking /Users/pchabelski/IdeaProjects/scala-cli-tests-2/untitled/17007/A.scala after phase posttyper
checking /Users/pchabelski/IdeaProjects/scala-cli-tests-2/untitled/17007/B.scala after phase posttyper
checking /Users/pchabelski/IdeaProjects/scala-cli-tests-2/untitled/17007/A.scala after phase pickler
checking /Users/pchabelski/IdeaProjects/scala-cli-tests-2/untitled/17007/B.scala after phase pickler
checking /Users/pchabelski/IdeaProjects/scala-cli-tests-2/untitled/17007/A.scala after phase inlining
checking /Users/pchabelski/IdeaProjects/scala-cli-tests-2/untitled/17007/A.scala after phase postInlining
checking /Users/pchabelski/IdeaProjects/scala-cli-tests-2/untitled/17007/A.scala after phase checkUnusedPostInlining
checking /Users/pchabelski/IdeaProjects/scala-cli-tests-2/untitled/17007/A.scala after phase staging
checking /Users/pchabelski/IdeaProjects/scala-cli-tests-2/untitled/17007/A.scala after phase splicing
checking /Users/pchabelski/IdeaProjects/scala-cli-tests-2/untitled/17007/A.scala after phase pickleQuotes
[error] ./A.scala:6:7
[error] class annotation needs to be abstract, since def transform
[error]   (using x$1: scala.quoted.Quotes)
[error]     (definition: x$1.reflect.Definition, companion:
[error]       Option[x$1.reflect.Definition]): List[x$1.reflect.Definition] in trait MacroAnnotation in package scala.annotation is not defined 
[error] (The class implements a member with a different type: def transform
[error]   (using x$1: scala.quoted.Quotes)
[error]     (tree: x$1.reflect.Definition): List[x$1.reflect.ClassDef] in class annotation)
[error] class annotation extends MacroAnnotation:
[error]       ^
Error compiling project (Scala 3.6.4-RC1, JVM (23))
Compilation failed