The driver-scala provides Scala-idiomatic wrappers for the Mongo Reactive Streams driver. It currently supports: Scala 2.11, Scala 2.12, Scala 2.13, and Scala 3.

Supported Scala versions and their exact version numbers are defined in gradle.properties:

• supportedScalaVersions — the list of supported Scala versions
• defaultScalaVersion — the version used when no -PscalaVersion flag is provided (currently 2.13)

The Scala source set configuration, compiler options, and dependency wiring are all handled in buildSrc/src/main/kotlin/project/scala.gradle.kts.

Scala library and test dependencies for each version are defined in gradle/libs.versions.toml. Look for entries prefixed with scala- in the [versions], [libraries], and [bundles] sections.

Source code is organized into version-specific directories. Shared code goes in the common scala directory, while version-specific code goes in the appropriate directory:

src/main/
├── scala/          # Shared code (all Scala versions)
├── scala-2/        # Scala 2 only (2.11, 2.12 and 2.13)
├── scala-2.13/     # Scala 2.13 only
├── scala-2.13-/    # Scala 2.12 & 2.11
├── scala-3/        # Scala 3 only

Test code also supports the same directory structure. The source sets for each Scala version are configured in buildSrc/src/main/kotlin/project/scala.gradle.kts. When adding new code, place it in the most general directory that applies. Only use a version-specific directory when the code requires syntax or APIs unique to that version.

Spotless defaults to Scala 2.13 formatting rules for all code apart from Scala 3 code.

For Scala 3 specific code, the bson-scala/build.gradle.kts shows how to configure Spotless to use a Scala 3 scalafmt config. It targets only files in **/scala-3/** and uses a separate config/scala/scalafmt-3.conf:

if (scalaVersion.equals("3")) {
    spotless {
        scala {
            clearSteps()
            target("**/scala-3/**")
            scalafmt("3.10.7").configFile(rootProject.file("config/scala/scalafmt-3.conf"))
        }
    }
}

Use this pattern in other build.gradle.kts files if they also contain Scala 3 specific code.

By default, tests run against Scala 2.13. To test against a specific Scala version, pass the -PscalaVersion flag:

# Test driver-scala with Scala 3
./gradlew :driver-scala:scalaCheck -PscalaVersion=3

# Test driver-scala with Scala 2.12
./gradlew :driver-scala:scalaCheck -PscalaVersion=2.12

# Test driver-scala with the default (2.13) against Java 8
./gradlew :driver-scala:scalaCheck -PjavaVersion=8