Add Scala3 support - and copy over some code as proof (#234)

Related => will-molloy/java-template#246
GitOrigin-RevId: 3ee4f8dae33f7065d3d911814574ef6296496542

Author: will-molloy

build.gradle.kts

@@ -5,14 +5,12 @@ import com.github.spotbugs.snom.SpotBugsExtension
 import com.github.spotbugs.snom.SpotBugsTask
 import org.gradle.api.tasks.testing.logging.TestExceptionFormat
 import org.gradle.api.tasks.testing.logging.TestLogEvent
-import org.jetbrains.kotlin.gradle.dsl.KotlinJvmProjectExtension
 
 logger.quiet("Java version: ${JavaVersion.current()}")
 logger.quiet("Gradle version: ${gradle.gradleVersion}")
 
 plugins {
   id("java-library")
-  kotlin("jvm") version libs.versions.kotlin
   alias(libs.plugins.spotless)
   alias(libs.plugins.spotbugs)
   alias(libs.plugins.buildtimetracker)
@@ -30,11 +28,6 @@ allprojects {
     targetCompatibility = JavaVersion.VERSION_21
   }
 
-  apply(plugin = "kotlin")
-  configure<KotlinJvmProjectExtension> {
-    jvmToolchain(21)
-  }
-
   apply(plugin = "com.diffplug.spotless")
   configure<SpotlessExtension> {
     // https://github.com/diffplug/spotless/tree/main/plugin-gradle#java
@@ -45,9 +38,6 @@ allprojects {
       endWithNewline()
     }
     // https://github.com/diffplug/spotless/tree/main/plugin-gradle#kotlin
-    // Compared to ktlint, it seems ktfmt is better for actual Kotlin code (more deterministic/consistent output).
-    // Furthermore, spotless is more for formatting than linting.
-    // However, it has some weird output with Gradle scripts, so using ktlint for that.
     kotlin {
       ktfmt().googleStyle()
       trimTrailingWhitespace()
@@ -58,9 +48,15 @@ allprojects {
       trimTrailingWhitespace()
       endWithNewline()
     }
+    // https://github.com/diffplug/spotless/tree/main/plugin-gradle#scala
+    scala {
+      scalafmt().configFile("$rootDir/scalafmt.conf")
+      trimTrailingWhitespace()
+      endWithNewline()
+    }
   }
 
-  // TODO Kotlin alternative?
+  // TODO Kotlin/Scala alternative?
   apply(plugin = "checkstyle")
   configure<CheckstyleExtension> {
     toolVersion = "10.12.0"
@@ -114,17 +110,6 @@ allprojects {
     }
   }
 
-  val previewFeatures = emptyList<String>()
-  tasks.withType<JavaCompile> {
-    options.compilerArgs = previewFeatures
-  }
-  tasks.withType<Test> {
-    jvmArgs = previewFeatures
-  }
-  tasks.withType<JavaExec> {
-    jvmArgs = previewFeatures
-  }
-
   dependencies {
     implementation(rootProject.libs.spotbugs.annotations)
 

gradle/libs.versions.toml

@@ -4,16 +4,18 @@ spotbugs = { id = "com.github.spotbugs", version = "6.0.27" }
 buildtimetracker = { id = "com.asarkar.gradle.build-time-tracker", version = "4.3.0" }
 
 [versions]
-kotlin = "2.1.0"
-log4j = "2.24.3"
 spotbugs = "4.8.6"
 guava = "33.4.0-jre"
+log4j = "2.24.3"
 commons-lang = "3.17.0"
 jackson = "2.18.2"
 # test libs
 junit = "5.11.4"
 truth = "1.4.4"
 mockito = "5.14.2"
+# langs
+scala = "3.6.2"
+kotlin = "2.1.0"
 
 [libraries]
 spotbugs-annotations = { module = "com.github.spotbugs:spotbugs-annotations", version.ref = "spotbugs" }
@@ -29,3 +31,5 @@ truth = { module = "com.google.truth:truth", version.ref = "truth" }
 mockito-core = { module = "org.mockito:mockito-core", version.ref = "mockito" }
 mockito-junit = { module = "org.mockito:mockito-junit-jupiter", version.ref = "mockito" }
 guava-testlib = { module = "com.google.guava:guava-testlib", version.ref = "guava" }
+# scala
+scala-library = { module = "org.scala-lang:scala3-library_3", version.ref = "scala" }

scalafmt.conf

@@ -0,0 +1,4 @@
+version = "3.7.3"
+runner.dialect = scala3
+maxColumn = 100
+docstrings.style = Asterisk

spotbugs-exclude.xml

@@ -1,7 +1,3 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <FindBugsFilter>
-<Match>
-  <!-- kotlin -->
-  <Bug pattern="BC_BAD_CAST_TO_ABSTRACT_COLLECTION"/>
-</Match>
 </FindBugsFilter>