Assertion error in DottyBackendInterface: denot.name is not default getter

[olafurpg]

After merging the fix for #2704, I'm hitting a new assertion error in the backend while trying to compile the scala/compiler-benchmark with Dotty.

To reproduce

cd dotty
git checkout 0109fef834b4f08ba4dbc0fd08fe6f05753cb9b1
export NIGHTLYBUILD=yes
sbt dotty-bootstrapped/publishLocal
cd target
git clone https://github.com/olafurpg/compiler-benchmark.git
cd compiler-benchmark
git checkout c30610306e9bc7b5ed0609f0f24ca1054a48d26f // branch dotty2
sbt ++0.2.0-bin-20170623-0109fef-NIGHTLY compilation/test
...
[error] Error while emitting ScalacBenchmark.scala
[error] assertion failed
java.lang.AssertionError: assertion failed
	at scala.Predef$.assert(Predef.scala:156)
	at dotty.tools.backend.jvm.DottyBackendInterface.emitArgument(DottyBackendInterface.scala:259)
	at dotty.tools.backend.jvm.DottyBackendInterface.emitAssocs$$anonfun$2(DottyBackendInterface.scala:315)
	at scala.compat.java8.JProcedure1.apply(JProcedure1.java:18)
	at scala.compat.java8.JProcedure1.apply(JProcedure1.java:10)
	at scala.collection.TraversableLike$WithFilter$$anonfun$foreach$1.apply(TraversableLike.scala:733)
	at scala.collection.immutable.List.foreach(List.scala:392)
	at scala.collection.TraversableLike$WithFilter.foreach(TraversableLike.scala:732)
	at dotty.tools.backend.jvm.DottyBackendInterface.emitAssocs(DottyBackendInterface.scala:315)
	at dotty.tools.backend.jvm.DottyBackendInterface.emitAnnotations$$anonfun$2(DottyBackendInterface.scala:308)

Compiling with -Ycheck:all gives a hint that an error occurred while typechecking this line here:
https://github.com/scala/compiler-benchmark/blob/d0f038e0a9f367e26dbe9825de9d00e9e699f592/compilation/src/main/scala/scala/tools/nsc/ScalacBenchmark.scala#L38

exception while typing java.nio.file.Files.walk(this.findSourceDir,
  [java.nio.file.FileVisitOption.FOLLOW_LINKS : java.nio.file.FileVisitOption]:
    Array[java.nio.file.FileVisitOption]
) of class class dotty.tools.dotc.ast.Trees$Apply # 11397
exception while typing java.nio.file.Files.walk(this.findSourceDir,
  [java.nio.file.FileVisitOption.FOLLOW_LINKS : java.nio.file.FileVisitOption]:
    Array[java.nio.file.FileVisitOption]
).collect of class class dotty.tools.dotc.ast.Trees$Select # 11399
exception while typing java.nio.file.Files.walk(this.findSourceDir,
  [java.nio.file.FileVisitOption.FOLLOW_LINKS : java.nio.file.FileVisitOption]:
    Array[java.nio.file.FileVisitOption]
).collect[java.util.List[java.nio.file.Path]^,
  java.util.stream.Collector[java.nio.file.Path, _,
    java.util.List[java.nio.file.Path]
  ]#A^
] of class class dotty.tools.dotc.ast.Trees$TypeApply # 11402

I unsuccessfully tried to minimize the error with

import java.nio.file._
import java.util.stream.Collectors
import scala.collection.JavaConverters._

object foo {
  Files.walk(Paths.get("."), FileVisitOption.FOLLOW_LINKS).collect(Collectors.toList[Path]).asScala
}

The failed assertion is here:
https://github.com/lampepfl/dotty/blob/7381e9d5106dec40cce70471c2c0c755b4bd374b/compiler/src/dotty/tools/backend/jvm/DottyBackendInterface.scala#L259

This issue is a blocker for merging scala/compiler-benchmark#31

[odersky]

In what phase did -Ycheck fail?

And, can you change the line that caused the assertion error to:

 assert(toDenot(t.symbol).name.is(DefaultGetterName), toDenot(t.symbol).name.debugString) // this should be default getter. 

It would be good to see what name it got.

[olafurpg]

-Ycheck failed after the frontend phase. I opened #2801 adding the debug string to the error message, which now reports

[info] checking /Users/ollie/dev/compiler-benchmark/compilation/src/main/scala/scala/tools/nsc/ScalacBenchmark.scala after phase frontend
exception while typing java.nio.file.Files.walk(this.findSourceDir,
  [java.nio.file.FileVisitOption.FOLLOW_LINKS : java.nio.file.FileVisitOption]:
    Array[java.nio.file.FileVisitOption]
) of class class dotty.tools.dotc.ast.Trees$Apply # 3099
...
found:    Array[java.nio.file.FileVisitOption]
[error] required: java.nio.file.FileVisitOption
[error]
[error]
[error] tree = [java.nio.file.FileVisitOption.FOLLOW_LINKS : java.nio.file.FileVisitOption]:
[error]   Array[java.nio.file.FileVisitOption]

[olafurpg]

The Array[nio.file.FileVisitOptions] error appears only with -Ycheck:all. Without -Ycheck, the assertion error becomes

[error] assertion failed: warmups[Unique $ 5]

The codebase has @Warmup annotations here but I couldn't find any references to warmup or unique.