Failure to load Seq with Scala 2 library TASTy with CC annotations

[nicolasstucki]

Followup to #19398.

Minimized code

// Test.scala
class Foo

sbt> set ThisBuild/Build.scala2Library := Build.Scala2LibraryCCTasty
sbt> scala3-bootstrapped/scalac Test.scala

Output

sbt:scala3> scala3-bootstrapped/scalac Test.scala
[info] running (fork) dotty.tools.dotc.Main -d dotty/compiler/../out/default-last-scalac-out.jar -classpath /Users/nicolasstucki/Library/Caches/Coursier/v1/https/repo1.maven.org/maven2/org/scala-lang/scala-library/2.13.12/scala-library-2.13.12.jar:dotty/library/../out/bootstrap/scala3-library-bootstrapped/scala-3.4.1-RC1-bin-SNAPSHOT-nonbootstrapped/scala3-library_3-3.4.1-RC1-bin-SNAPSHOT.jar:dotty/scala2-library-cc-tasty/../out/bootstrap/scala2-library-cc-tasty/scala-3.4.1-RC1-bin-SNAPSHOT-nonbootstrapped/scala2-library-cc-tasty_3-3.4.1-RC1-bin-SNAPSHOT.jar Test.scala
Exception in thread "main"
  unhandled exception while running MegaPhase{elimErasedValueType, pureStats, vcElideAllocations, etaReduce, arrayApply, elimPolyFunction, tailrec, completeJavaEnums, mixin, lazyVals, memoize, nonLocalReturns, capturedVars} on Test.scala

  An unhandled exception was thrown in the compiler.
  Please file a crash report here:
  https://github.com/lampepfl/dotty/issues/new/choose
  For non-enriched exceptions, compile with -Yno-enrich-error-messages.

     while compiling: Test.scala
        during phase: MegaPhase{elimErasedValueType, pureStats, vcElideAllocations, etaReduce, arrayApply, elimPolyFunction, tailrec, completeJavaEnums, mixin, lazyVals, memoize, nonLocalReturns, capturedVars}
                mode: Mode(ImplicitsEnabled)
     library version: version 2.13.12
    compiler version: version 3.4.1-RC1-bin-SNAPSHOT-git-2b40f55
            settings: -classpath ~/Library/Caches/Coursier/v1/https/repo1.maven.org/maven2/org/scala-lang/scala-library/2.13.12/scala-library-2.13.12.jar:dotty/library/../out/bootstrap/scala3-library-bootstrapped/scala-3.4.1-RC1-bin-SNAPSHOT-nonbootstrapped/scala3-library_3-3.4.1-RC1-bin-SNAPSHOT.jar:dotty/scala2-library-cc-tasty/../out/bootstrap/scala2-library-cc-tasty/scala-3.4.1-RC1-bin-SNAPSHOT-nonbootstrapped/scala2-library-cc-tasty_3-3.4.1-RC1-bin-SNAPSHOT.jar -d /
dotty.tools.dotc.core.CyclicReference: Cyclic reference involving trait Seq

 Run with -explain-cyclic for more details.

[nicolasstucki]

It happens in the arrayApply mini phase.

[odersky]

#19603 fixes the basics and we can now compile most tests.

I tried to go further with

sbt> set ThisBuild/Build.scala2Library := Build.Scala2LibraryCCTasty
sbt> scala3-bootstrapped/testCompilation

Here's the current list of failures:

32 suites passed, 4 failed, 36 total
    tests/neg/i8988.scala failed
    tests/neg/abstract-givens.scala failed
    tests/neg/i18682.scala failed
    tests/run/enrich-gentraversable.scala failed
    tests/run/t5328.scala failed
    tests/run/xml.scala failed
    tests/run/t4332b.scala failed
    tests/run/abstract-givens.scala failed
    tests/run/t2552.scala failed
    tests/run/t2544.scala failed
    tests/run/i16459.scala failed
    tests/run/t6114.scala failed
    tests/pos/i18345.scala failed
    tests/run/t3269.scala failed
    tests/pos/spec-asseenfrom.scala failed
    tests/pos/i19009.case1.scala failed
    tests/pos/i14966a.scala failed
    tests/run/iterables.scala failed
    tests/run/i14582.scala failed
    tests/run/t4054.scala failed
    tests/pos/i14953.scala failed
    tests/run/t5201.scala failed
    tests/run/t6968.scala failed
    tests/run/range-unit.scala failed
    tests/pos/t5120.scala failed
    tests/run/t6271.scala failed
    tests/run/enrich-gentraversable.scala failed
    tests/pos/i1036.scala failed
    tests/pos/t6925.scala failed
    tests/run/Course-2002-10.scala failed
    tests/pos/tyql.scala failed
    tests/run/t4288.scala failed
    tests/run/main-annotation-newMain.scala failed
    tests/run/Pouring.scala failed
    tests/run/t5328.scala failed
    tests/run/t6628.scala failed
    tests/run/arrayview.scala failed
    tests/run/colltest1.scala failed
    tests/pos/gadt-accumulatable.scala failed
    tests/run/t3397.scala failed
    tests/run/t2544.scala failed
    tests/run/i16459.scala failed
    tests/run/t3516.scala failed
    tests/pos/tcpoly_ticket2096.scala failed
    tests/run/t4582.scala failed
    tests/run/i4523.scala failed
    tests/run/iterators.scala failed
    tests/run/stream-stack-overflow-filter-map.scala failed
    tests/pos/t4716.scala failed
    tests/run/streamWithFilter.scala failed
    tests/run/IArrayOps.scala failed
    tests/run/ReverseSeqView.scala failed
    tests/run/viewtest.scala failed
    tests/run/numbereq.scala failed
    tests/run/t3760.scala failed
    tests/run/distinct.scala failed
    tests/run/t4332b.scala failed
    tests/pos/i6199a.scala failed
    tests/run/view-headoption.scala failed
    tests/run/abstract-givens.scala failed
    tests/pos/i9967.scala failed
    tests/pos/i1777.scala failed
    tests/pos/StringContext.scala failed
    tests/run/t4954.scala failed
    tests/pos/i5418.scala failed
    tests/run/t6584.scala failed
    tests/run/extmethods2.scala failed
    tests/pos/t0068.scala failed
    tests/run/kmpSliceSearch.scala failed
    tests/run/patmat-bind-typed.scala failed
    tests/run/t1220.scala failed
    tests/run/t5867.scala failed
    tests/pos/syntaxRewrites.scala failed
    tests/run/forvaleq.scala failed
    tests/pos/t6205.scala failed
    tests/run/Pouring2.scala failed
    tests/run/unittest_iterator.scala failed
    tests/pos/indent-colons.scala failed
    tests/pos/t4717.scala failed
    tests/run/t2552.scala failed
    tests/run/lst failed
    tests/run/t5053.scala failed
    tests/run/lists-run.scala failed
    tests/run/t1074.scala failed
    tests/run/seqlike-kmp.scala failed
    tests/pos/tyql.scala failed
    tests/pos/t6925.scala failed

We need to follow up on this next.

[nicolasstucki]

Moving the followup discussion to #19652.

The original issue is fixed and we have regression tests.