LinkageError: “scala/collection/Seq” when using another IntelliJ plugin written in Scala

[hmemcpy]

TL;DR HaskForce bundles a scala-library jar which interferes with other IntelliJ plugins written in Scala.

Details:
We have an IntelliJ plugin that is written in mostly Scala, and one of our users complained that on occasion, an exception:

java.lang.LinkageError: loader constraint violation: loader (instance of com/intellij/ide/plugins/cl/PluginClassLoader) previously initiated loading for a different type with name "scala/collection/Seq"
    at ...

would appear. I couldn't initially reproduce it, until I asked the affected user to dump the contents of their plugins directory. I suspected a conflicting scala version was somehow interfering with the plugin. After running find . | grep scala-, here is what I saw:

./HaskForce/lib/scala-library-2.12.4.jar
./HaskForce/lib/scala-reflect-2.12.4.jar
./Scala/lib/scala-nailgun-runner.jar
./Scala/lib/scala-library.jar
./Scala/lib/scala-play-2-jps-plugin.jar
./Scala/lib/scala-reflect.jar
./Scala/lib/scala-xml.jar
./Scala/lib/scala-parser-combinators_2.12-1.0.6.jar

It seems HaskForce is bundling a specific scala-library 2.12.4. On a hunch, I asked the user to remove HaskForce, and after IntelliJ restart, the problem disappeared!

I believe the problem is caused by using compile instead of implementation in the gradle script, which causes the scala-library jar to be bundled.

[carymrobbins]

If I recall correctly, IntelliJ's class loader should allow for this. Is your plugin open sourced? Would be interesting for me to look at to see how to resolve. I will double check as well to confirm that HaskForce's class loader is doing the right thing.

[hmemcpy]

The strange thing is, Scala plugin also bundles its own scala-library.jar, it seems, but it's without any version information... I'm not sure how this works to be honest, whether the jar name/version has any part in it).

The plugin is not opensource, unfortunately, but let me try to get a small repro. If my suspicions are correct, this surely would affect other plugins written in Scala...

[puffnfresh]

I have a coworker hitting the same problem (but different class) - I've asked them to disable a bunch of their plugins to see if we can narrow down to which one is a problem.

[hmemcpy]

@puffnfresh Can you ask them to look for plugins that have scala-library.2.12.x.jar included? Maybe will be a hint :)

[carymrobbins]

I think the problem is that I'm using the following in the plugin.xml -

<idea-plugin use-idea-classloader="true">

According to the docs

A separate class loader is used to load the classes of each plugin. This allows each plugin to use a different version of a library, even if the same library is used by the IDE itself or by another plugin.

So I need to remove that attribute from the plugin.xml and ensure classes are still resolved properly.

@hmemcpy - I would also make sure that the closed-source plugin being used is also not using this attribute as that may be part of the problem as well.

[carymrobbins]

@hmemcpy - I've cut a pre-release which contains a fix for this - v0.3.43-SNAPSHOT-b5425ef8

Could you have the user install this version and see if it alleviates the issue?

[hmemcpy]

Hey! Sorry for the lack of response. Thanks for the fix, let me try it (as well as the suggestion above) and I'll report back.

[hmemcpy]

Updates! I first tried seeing if my plugin was using use-idea-classloader="true" - it wasn't, and when I tried adding it myself (with false), I got a strikethrough on it, with a hint that this option is deprecated!

I installed the pre-release version and can confirm the problem was resolved! Before installing it, my sandboxed instance with HaskForce and my plugin was throwing this exception, after loading the pre-release - the problem disappeared!

Thank you very much!

[carymrobbins]

Fantastic! I'll work on cutting a full release for this, thanks for the report!