Tests with explicit nulls are broken on main branch

[noti0na1]

It seems the CI is failing on main branch because of the PR #22473.

The errors only happen in "Test Suite with the CC Standard Library". Maybe related to cc library compiled in explicit nulls?

One of the failed tests is a debug test introduced by #22597, but the error message does not give much information...

Error:  Debug step failed: tests/debug-custom-args/eval-explicit-nulls.check:3
Evaluation failed:
-- [E170] Type Error: <expression class>:12:28 -------------------------------------------------------------------------
12 |    if idx == -1 then throw new NoSuchElementException(name)
   |                            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   |                            NoSuchElementException is not a class type
   |
   | longer explanation available when compiling with `-explain`-- [E170] Type Error: <expression class>:18:28 -------------------------------------------------------------------------
18 |    if idx == -1 then throw new NoSuchElementException(name)
   |                            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   |                            NoSuchElementException is not a class type
   |
   | longer explanation available when compiling with `-explain`
Error:  Test dotty.tools.debug.DebugTests.debug failed: java.lang.AssertionError: Debug test failed, but should not, reasons:
Error:  encountered 1 test failure(s):
Error:    - generic failure (see test output), took 74.963 sec
Error:      at dotty.tools.vulpix.ParallelTesting$CompilationTest.checkPass(ParallelTesting.scala:1269)
Error:      at dotty.tools.debug.DebugTests$.dotty$tools$debug$DebugTests$$$checkDebug(DebugTests.scala:45)
Error:      at dotty.tools.debug.DebugTests.debug(DebugTests.scala:23)
Error:      at jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
Error:      at jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:77)
Error:      at jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
Error:      at java.lang.reflect.Method.invoke(Method.java:569)
Error:      ...

cc @HarrisL2 @olhotak

[olhotak]

Have you found a way to reproduce it in sbt? I haven't yet.

I would guess it's probably some interaction between CC, which wraps types in Tasty inside AnnotatedType, and #22473, which wraps types coming from Tasty in a FlexibleType. Maybe the two wrappers are interfering and the check for a class type can't see through both of them.

But first I need to be able to reproduce it outside of the CI.

[olhotak]

But I see that this is only one of many errors.

We should revert #22473, figure out how to run these tests outside of CI, and then debug it offline before merging it again.

[olhotak]

The following sbt commands reproduce this:

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

[olhotak]

For the specific test mentioned above, it's:

set ThisBuild/Build.scala2Library := Build.Scala2LibraryCCTasty
scala3-bootstrapped/testOnly * -- *debug

[olhotak]

It seems the problems are unrelated to CC. The same errors come up with

set ThisBuild/Build.scala2Library := Build.Scala2LibraryTasty

So just having the standard library coming from Tasty is enough to cause the errors.