Wrong source when mixing inline and transparent inline

[odersky]

Compiler version

3.2.2 RC2

Minimized example

Two files.

// boundary.scala
object boundary:
  transparent inline def apply[R](inline body: R): R =  // works if `transparent` is dropped
    body

2nd file:

// Test.scala
inline def f [T](fallback: => T) = fallback
def foo(x: Int): Int = boundary.apply {
  f(10)
}

Output

Under -Ycheck:all:

*** error while checking Test.scala after phase inlining ***
java.lang.AssertionError: assertion failed: wrong source set for 10 # -1 of class dotty.tools.dotc.ast.Trees$Literal, set to boundary.scala but context had Test.scala
 <permanent> while running Ycheck on Test.scala
exception occurred while compiling Test.scala, boundary.scala
java.lang.AssertionError: assertion failed: wrong source set for 10 # -1 of class dotty.tools.dotc.ast.Trees$Literal, set to boundary.scala but context had Test.scala
 <permanent> while compiling Test.scala, boundary.scala
Exception in thread "main" java.lang.AssertionError: assertion failed: wrong source set for 10 # -1 of class dotty.tools.dotc.ast.Trees$Literal, set to boundary.scala but context had Test.scala
 <permanent>
	at scala.runtime.Scala3RunTime$.assertFailed(Scala3RunTime.scala:8)
	at dotty.tools.dotc.transform.YCheckPositions$$anon$1.traverse(YCheckPositions.scala:36)
	at dotty.tools.dotc.transform.YCheckPositions$$anon$1.traverse(YCheckPositions.scala:45)
	at dotty.tools.dotc.ast.Trees$Instance$TreeTraverser.apply(Trees.scala:1655)
	at dotty.tools.dotc.ast.Trees$Instance$TreeTraverser.apply(Trees.scala:1655)
	at dotty.tools.dotc.ast.Trees$Instance$TreeAccumulator.foldOver(Trees.scala:1554)
	at dotty.tools.dotc.ast.Trees$Instance$TreeTraverser.traverseChildren(Trees.scala:1656)

Expectation

Should pass Ycheck

[julienrf]

Might be related or solved by #15684

[nicolasstucki]

Compiling this with -Xprint-inline shows that after inlining we have

   def foo(x: Int): Int =
      {{/* inlined from boundary */
        {{/* inlined from outside */
          {{/* inlined from f[Int](10) */{{/* inlined from outside */10}}:Int}}
          }}
      }}

This implies that the Inlined tree nodes are correct.

The issue must be that we copy the Literal tree for 10 with a context that has the wrong source set.

[nicolasstucki]

Compiling with -Ydebug-tree-with-id -2 I got the id of the failing Literal. Lets say 716 as an example.

java.lang.AssertionError: assertion failed: wrong source set for 10 # 716 of class dotty.tools.dotc.ast.Trees$Literal, set to tests/pos/i16609/boundary.scala but context had tests/pos/i16609/Test.scala

Re-compiling with -Ydebug-tree-with-id 716 we get the following stack dump when that node is created.

Stack dump

Debug tree (id=716) creation 
Literal(Constant(10))
        at java.base/java.lang.Thread.dumpStack(Thread.java:1380)
        at dotty.tools.dotc.ast.Positioned.allocateId(Positioned.scala:38)
        at dotty.tools.dotc.ast.Positioned.<init>(Positioned.scala:40)
        at dotty.tools.dotc.ast.Trees$Tree.<init>(Trees.scala:50)
        at dotty.tools.dotc.ast.Trees$Literal.<init>(Trees.scala:533)
        at dotty.tools.dotc.ast.untpd$.Literal(untpd.scala:380)
        at dotty.tools.dotc.ast.tpd$.Literal(tpd.scala:58)
        at dotty.tools.dotc.ast.tpd$.singleton(tpd.scala:450)
        at dotty.tools.dotc.inlines.Inliner.$anonfun$6(Inliner.scala:586)
        at dotty.tools.dotc.ast.TreeTypeMap.transform(TreeTypeMap.scala:94)
        at dotty.tools.dotc.ast.Trees$Instance$TreeMap.transform(Trees.scala:1418)
        at dotty.tools.dotc.ast.TreeTypeMap.transform(TreeTypeMap.scala:145)
        at dotty.tools.dotc.inlines.Inliner.inlined(Inliner.scala:614)
        at dotty.tools.dotc.inlines.Inlines$InlineCall.expand(Inlines.scala:444)
        at dotty.tools.dotc.inlines.Inlines$.inlineCall(Inlines.scala:151)
        at dotty.tools.dotc.transform.Inlining$InliningTreeMap.transform(Inlining.scala:84)
        at dotty.tools.dotc.ast.Trees$Instance$TreeMap.transform(Trees.scala:1444)
        at dotty.tools.dotc.ast.TreeMapWithImplicits.transform(TreeMapWithImplicits.scala:73)
        at dotty.tools.dotc.transform.Inlining$InliningTreeMap.transform(Inlining.scala:90)
        at dotty.tools.dotc.ast.Trees$Instance$TreeMap.transform(Trees.scala:1444)
        at dotty.tools.dotc.ast.TreeMapWithImplicits.transform(TreeMapWithImplicits.scala:73)
        at dotty.tools.dotc.transform.Inlining$InliningTreeMap.transform(Inlining.scala:90)
        at dotty.tools.dotc.ast.TreeMapWithImplicits.transform(TreeMapWithImplicits.scala:56)
        at dotty.tools.dotc.transform.Inlining$InliningTreeMap.transform(Inlining.scala:78)
        at dotty.tools.dotc.ast.tpd$TreeMapWithPreciseStatContexts.loop$2(tpd.scala:1225)
        at dotty.tools.dotc.ast.tpd$TreeMapWithPreciseStatContexts.transformStats(tpd.scala:1225)
        at dotty.tools.dotc.ast.tpd$TreeMapWithPreciseStatContexts.transformStats(tpd.scala:1227)
        at dotty.tools.dotc.ast.TreeMapWithImplicits.transform(TreeMapWithImplicits.scala:64)
        at dotty.tools.dotc.transform.Inlining$InliningTreeMap.transform(Inlining.scala:90)
        at dotty.tools.dotc.ast.Trees$Instance$TreeMap.transform(Trees.scala:1478)
        at dotty.tools.dotc.ast.TreeMapWithImplicits.transform(TreeMapWithImplicits.scala:73)
        at dotty.tools.dotc.transform.Inlining$InliningTreeMap.transform(Inlining.scala:78)
        at dotty.tools.dotc.ast.tpd$TreeMapWithPreciseStatContexts.loop$2(tpd.scala:1225)
        at dotty.tools.dotc.ast.tpd$TreeMapWithPreciseStatContexts.transformStats(tpd.scala:1225)
        at dotty.tools.dotc.ast.tpd$TreeMapWithPreciseStatContexts.transformStats(tpd.scala:1227)
        at dotty.tools.dotc.ast.Trees$Instance$TreeMap.transform(Trees.scala:1486)
        at dotty.tools.dotc.ast.TreeMapWithImplicits.transform(TreeMapWithImplicits.scala:73)
        at dotty.tools.dotc.transform.Inlining$InliningTreeMap.transform(Inlining.scala:90)
        at dotty.tools.dotc.transform.Inlining$$anon$2.transform(Inlining.scala:62)
        at dotty.tools.dotc.transform.MacroTransform.run(MacroTransform.scala:18)
        at dotty.tools.dotc.transform.Inlining.run(Inlining.scala:34)
        at dotty.tools.dotc.core.Phases$Phase.runOn$$anonfun$1(Phases.scala:324)
        at scala.collection.immutable.List.map(List.scala:246)
        at dotty.tools.dotc.core.Phases$Phase.runOn(Phases.scala:328)
        at dotty.tools.dotc.transform.Inlining.runOn(Inlining.scala:38)
        at dotty.tools.dotc.Run.runPhases$1$$anonfun$1(Run.scala:244)
        at scala.runtime.function.JProcedure1.apply(JProcedure1.java:15)
        at scala.runtime.function.JProcedure1.apply(JProcedure1.java:10)
        at scala.collection.ArrayOps$.foreach$extension(ArrayOps.scala:1321)
        at dotty.tools.dotc.Run.runPhases$1(Run.scala:260)
        at dotty.tools.dotc.Run.compileUnits$$anonfun$1(Run.scala:268)
        at dotty.tools.dotc.Run.compileUnits$$anonfun$adapted$1(Run.scala:277)
        at dotty.tools.dotc.util.Stats$.maybeMonitored(Stats.scala:68)
        at dotty.tools.dotc.Run.compileUnits(Run.scala:277)
        at dotty.tools.dotc.Run.compileSources(Run.scala:195)
        at dotty.tools.dotc.Run.compile(Run.scala:179)
        at dotty.tools.dotc.Driver.doCompile(Driver.scala:35)
        at dotty.tools.dotc.Driver.process(Driver.scala:195)
        at dotty.tools.dotc.Driver.process(Driver.scala:163)
        at dotty.tools.dotc.Driver.process(Driver.scala:175)
        at dotty.tools.dotc.Driver.main(Driver.scala:205)
        at dotty.tools.dotc.Main.main(Main.scala)

The following line seems to be the place where we need to fix this

        at dotty.tools.dotc.ast.tpd$.singleton(tpd.scala:450)
        at dotty.tools.dotc.inlines.Inliner.$anonfun$6(Inliner.scala:586)

We need to make sure that the correct context is set when we call singleton in the inliner. What is not clear yet is why the context does not have the correct source position.

https://github.com/lampepfl/dotty/blob/main/compiler/src/dotty/tools/dotc/inlines/Inliner.scala#L586