Regression SpaceEngine wrt 3.3.0

[Adam-Vandervorst]

3.3.1

Minimized code

running compile on
https://github.com/Adam-Vandervorst/CZ2

Output (click arrow to expand)

[info] compiling 13 Scala sources to /home/adam/IdeaProjects/CZ2/jvm/target/scala-3.3.1/classes ...
  unhandled exception while running MegaPhase{protectedAccessors, extmethods, uncacheGivenAliases, elimByName, hoistSuperArgs, forwardDepChecks, specializeApplyMethods, tryCatchPatterns, patternMatcher} on /home/adam/IdeaProjects/CZ2/shared/src/main/scala/ExprMap.scala

  An unhandled exception was thrown in the compiler.
  Please file a crash report here:
  https://github.com/lampepfl/dotty/issues/new/choose

     while compiling: <no file>
        during phase: <no phase>
                mode: Mode(ImplicitsEnabled)
     library version: version 2.13.10
    compiler version: version 3.3.1
            settings: -bootclasspath /home/adam/.cache/coursier/v1/https/repo1.maven.org/maven2/org/scala-lang/scala3-library_3/3.3.1/scala3-library_3-3.3.1.jar:/home/adam/.cache/coursier/v1/https/repo1.maven.org/maven2/org/scala-lang/scala-library/2.13.10/scala-library-2.13.10.jar -classpath /home/adam/IdeaProjects/CZ2/jvm/target/scala-3.3.1/classes -d /home/adam/IdeaProjects/CZ2/jvm/target/scala-3.3.1/classes

                tree: EmptyTree
       tree position: :<unknown>
           tree type: <notype>
              symbol: val <none>
           call site: package <root> in module class <root>

  == Source file context for tree position ==
error] ## Exception when compiling 14 sources to /home/adam/IdeaProjects/CZ2/jvm/target/scala-3.3.1/classes
[error] java.lang.StackOverflowError
[error] dotty.tools.dotc.core.Types$Type.findMember(Types.scala:886)
[error] dotty.tools.dotc.core.Types$Type.memberBasedOnFlags(Types.scala:678)
[error] dotty.tools.dotc.core.Types$Type.member(Types.scala:662)
[error] dotty.tools.dotc.typer.Applications$.extractorMember(Applications.scala:44)
[error] dotty.tools.dotc.typer.Applications$.extractorMemberType(Applications.scala:47)
[error] dotty.tools.dotc.typer.Applications$.$anonfun$42(Applications.scala:113)
[error] dotty.tools.dotc.typer.Applications$.$anonfun$adapted$3(Applications.scala:113)
[error] scala.collection.Iterator$$anon$9.next(Iterator.scala:584)
[error] scala.collection.Iterator$$anon$11.hasNext(Iterator.scala:637)
[error] scala.collection.immutable.List.prependedAll(List.scala:152)
[error] scala.collection.IterableOnceOps.toList(IterableOnce.scala:1288)
[error] scala.collection.IterableOnceOps.toList$(IterableOnce.scala:1288)
[error] scala.collection.AbstractIterator.toList(Iterator.scala:1300)
[error] dotty.tools.dotc.typer.Applications$.productSelectorTypes(Applications.scala:114)
[error] dotty.tools.dotc.transform.patmat.SpaceEngine$.isCheckable$1(Space.scala:845)
[error] dotty.tools.dotc.transform.patmat.SpaceEngine$.isCheckable$1$$anonfun$1(Space.scala:845)
[error] scala.collection.immutable.List.exists(List.scala:395)
(last three lines repeated)

Note

It doesn't crash on 3.3.0

[Gedochao]

@Adam-Vandervorst can you help to minimise the code for the replication of this crash?

[Adam-Vandervorst]

Since the error doesn't show a single call originating from the project, I am still trying to figure out where to start.
Do you have any pointers?

[Adam-Vandervorst]

The project is quite "low-tech" Scala. It doesn't use any imports or any fancy type constructions (I learned my lesson with #15992). Nonetheless, there are some things one of you may recognize as suspicious, together with the changes made from 3.3.0 to 3.3.1.
https://github.com/Adam-Vandervorst/CZ2/blob/aaa8aa58173df13996fb31fcfc182ba158d4681f/shared/src/main/scala/utils.scala#L19
https://github.com/Adam-Vandervorst/CZ2/blob/aaa8aa58173df13996fb31fcfc182ba158d4681f/shared/src/main/scala/utils.scala#L28
https://github.com/Adam-Vandervorst/CZ2/blob/aaa8aa58173df13996fb31fcfc182ba158d4681f/shared/src/main/scala/utils.scala#L31
https://github.com/Adam-Vandervorst/CZ2/blob/aaa8aa58173df13996fb31fcfc182ba158d4681f/shared/src/main/scala/ExprMapEngine.scala#L58
https://github.com/Adam-Vandervorst/CZ2/blob/aaa8aa58173df13996fb31fcfc182ba158d4681f/shared/src/main/scala/evaluation.scala#L39
https://github.com/Adam-Vandervorst/CZ2/blob/aaa8aa58173df13996fb31fcfc182ba158d4681f/shared/src/main/scala/ExprMap.scala#L47
https://github.com/Adam-Vandervorst/CZ2/blob/aaa8aa58173df13996fb31fcfc182ba158d4681f/shared/src/main/scala/ExprMap.scala#L328
https://github.com/Adam-Vandervorst/CZ2/blob/aaa8aa58173df13996fb31fcfc182ba158d4681f/shared/src/main/scala/ExprMap.scala#L129
https://github.com/Adam-Vandervorst/CZ2/blob/aaa8aa58173df13996fb31fcfc182ba158d4681f/shared/src/main/scala/Expr.scala#L239
https://github.com/Adam-Vandervorst/CZ2/blob/aaa8aa58173df13996fb31fcfc182ba158d4681f/shared/src/main/scala/RangeStorage.scala#L15

[Gedochao]

Since the error doesn't show a single call originating from the project, I am still trying to figure out where to start.
Do you have any pointers?

@Adam-Vandervorst as much as I'd like to help, not really.

     while compiling: <no file>
        during phase: <no phase>

we don't know the particular file or phase.

tree: EmptyTree
       tree position: :<unknown>
           tree type: <notype>
              symbol: val <none>
           call site: package <root> in module class <root>

the output we see here doesn't give virtually anything to go on, as far as I can tell.

What I imagine minimising this issue would entail is to take a look at your whole build and try to strip it of code while checking if the issue is replicable to try to pinpoint on where is the cause.
We need a snippet of code which would allow to replicate it.
As this would require some understanding of your project, it's likely that you are in the best position to try it.
I wish I could give you any better pointers here, but there's just not much to go on here.

https://github.com/lampepfl/dotty/blob/release-3.3.1/compiler/src/dotty/tools/dotc/core/Types.scala#L886
I believe the stack overflow happens on this recursive call, but this doesn't tell a whole lot, either (to me at the very least it doesn't).

Of course, we won't ignore this, as it's evidently a compiler crash and seems like a possible regression, but thorough investigation on the compiler team's side may take time.
Let me know if I can help.

[Adam-Vandervorst]

we don't know the particular file or phase.

Out of curiosity, what could've caused this info to be unavailable?

[SethTisue]

Just checking: is it the same on 3.4.0-RC2?

[Gedochao]

unhandled exception while running MegaPhase{protectedAccessors, extmethods, uncacheGivenAliases, elimByName, hoistSuperArgs, forwardDepChecks, specializeApplyMethods, tryCatchPatterns, patternMatcher} on /home/adam/IdeaProjects/CZ2/shared/src/main/scala/ExprMap.scala

Actually I haven't noticed earlier, but it seems we do know the exact file it breaks on: /home/adam/IdeaProjects/CZ2/shared/src/main/scala/ExprMap.scala

I suppose there's a separate bug in crash reporting, as the rest of the log doesn't point anywhere concrete.
We'll be able to extract that to a separate issue when we're able to minimise this.

Based on that, the megaphase seems to be this: https://github.com/lampepfl/dotty/blob/721e7c87ee95b811984b7b992728729d7094c4c4/compiler/src/dotty/tools/dotc/Compiler.scala#L75-L83
@Adam-Vandervorst I hope that narrows it down at least a little bit

[Adam-Vandervorst]

@SethTisue yes, it also crashes on 3.4.0-RC2.

@Gedochao thanks, I'll try and surface some of the suspicious pattern matching in that file, or try and comment it out.

[scala-center-bot]

This issue was picked for the Issue Spree No. 42 of February 6th, 2024. @dwijnand, @EugeneFlesselle, @jan-pieter will be working on it. If you have any insight into the issue or guidance on how to fix it, please leave it here.