Java arguments specified via jvmArgs are ignored for incremental compilation

[tashoyan]

The original goal was to increase Java stack size for the Scala compilation with help of the -Xss Java argument:

<plugin>
  <groupId>net.alchim31.maven</groupId>
  <artifactId>scala-maven-plugin</artifactId>
  <configuration>
    ...
    <jvmArgs>
      <jvmArg>-Xss2m</jvmArg>
    </jvmArgs>
    ...
  </configuration>
<plugin>

It looks like all settings from jvmArgs are completely ignored for the goals compile and testCompile.
Surprisingly, jvmArgs are effective (not ignored) for the goal doc-jar.
The problem occurs for scala-maven-plugin versions starting from 4.0.0. For the version 3.4.6 the problem does not occur.

This is a severe problem, as it leaves no possibility to overcome StackOverflowError during Scala compilation. For example: Stackoverflow in typechecker.Typers$Typer.

I am attaching a simple Maven project illustrating the problem. Here the JVM argument -XshowSettings:all is used as a marker: JVM settings are printed only when running the goal doc-jar - neither compile nor testCompile goals.
scalac-xss.tar.gz

java -version
openjdk version "1.8.0_292"
OpenJDK Runtime Environment (AdoptOpenJDK)(build 1.8.0_292-b10)
OpenJDK 64-Bit Server VM (AdoptOpenJDK)(build 25.292-b10, mixed mode)

[davidB]

For compile and testCompile, jvmArgs are only used when recompilationMode is all. Since 4.5.0 the default value is incremental, in this case compilation (zinc based) is made in the same jvm than maven.

[tashoyan]

If we use the default value of recompileMode, then we have to tune the settings of the JVM running Maven. We can do it by putting a file .mvn/jvm.config in the project directory, as described in Maven configuration. This works!
Maybe makes sense to describe this behavior in the documentation. Otherwise, it is quite difficult to figure out, how to customize JVM settings for Scala compilation.

[slandelle]

I'm going to try and fix this.

[slandelle]

So actually, this is super complicated to implement. The incremental compiler needs a huge amount of parameters, it would be a huge effort. Not impossible, but not something I'll be able to tackle any time soon.

As a workaround, I think we could:

1. either disable the incremental mode when jvmArgs are defined
2. or default to all instead of incremental when jvmArgs are defined and crash if incremental is explicitly defined along with jvmArgs

@davidB WDYT?

[davidB]

I prefer 2. (less magic/hidden behavior for end-user). I guess by "crash" you mean exit with an error message to explain the cause.

Thanks @slandelle for your support.

[slandelle]

@davidB Actually, I ended up implementing the process forking. PTAL #659

[slandelle]

Fixed in 4.8.0