Order of Scala compile options not maintained

[s-nel]

Describe the bug

The order of -Wconf options is important in evaluating which warning configuration rules apply. In Scala 2.13.15 the last matching rule will apply. In Gradle everything works and the order we specify the -Wconf is respected, however when we export the Bloop build, the order is completely changed.

That's because this plugin converts the list of options into a set and then sorts the set.

gradle-bloop/src/main/scala/bloop/integrations/gradle/model/BloopConverter.scala

Lines 1237 to 1254 in be6e34b

	val additionalOptions: Set[String] = {
	val opts = options.getAdditionalParameters
	if (opts == null) Set.empty
	else {
	// scalac options are passed back as Strings but under the hood can be GStringImpls which aren't Strings - so cope with that
	val optionList =
	opts.asScala.toList
	.asInstanceOf[List[Object]]
	.filter(_ != null)
	.map(_.toString)
	fuseOptionsWithArguments(optionList).toSet
	}
	}
	// Sort compiler flags to get a deterministic order when extracting the project
	splitFlags(
	baseOptions.union(loggingPhases).union(additionalOptions).toList.sorted
	)

Expected behavior

The order of Scala compiler options should match exactly what Gradle uses to compile Scala.

Operating system

macOS

Version of Gradle

7.6.4

Version of gradle-bloop

1.6.2

Version of Bloop

1.5.15

[Arthurm1]

@s-nel Can you give an example of your multiple -Wconf options. I'd thought -Wconf was a single setting with multiple options separated by commas.

i.e. -Wconf:<filters>:<action>,<filters>:<action>,...

[tgodzik]

You can actually split that into multiple options and there are some rules on how it will be joined. In some cases it might be necessary to split.

[s-nel]

We have a multi-project Gradle build. There is a base Gradle build that defines Scala options for all projects, but then individual projects have some additional options to ignore warnings from generated code

Something like this in the base build:

subprojects {
    ...

    tasks.withType<ScalaCompile>().configureEach {
        scalaCompileOptions.apply {
            ...
            additionalParameters = mutableListOf(
                "-Wconf:cat=deprecation:w,msg=-target is deprecated:s",
                ...
            )
        }
    }
}

Then in the sub project:

tasks.withType<ScalaCompile>().configureEach {
    scalaCompileOptions.apply {
        ...
        additionalParameters?.let {
            // Ignore warnings from our generated sources
            it.add("-Wconf:src=.*/generated_code/.*:s")
        }
    }
}

Since the order isn't maintained in Gradle Bloop plugin, we get different build outcomes in Gradle and Bloop.

We had a similar issue if we set deprecation = true in the base build and add -Wconf options in the sub projects. We can order it properly for the Gradle build to achieve the effect we want, but it will be in a completely different order in Bloop.