move scala and cross publish settings into plugins 🚀

Author: mcanlas

build.sbt

@@ -1,29 +1,18 @@
-val commonSettings = Seq(
-  organization       := "com.htmlism",
-  scalaVersion       := "2.13.18",
-  crossScalaVersions := Seq("2.13.18"),
-  scalacOptions += "-Xsource:3"
-)
-
 lazy val core = Project("spawning-pool-core", file("spawning-pool-core"))
-  .settings(commonSettings*)
   .settings(specs2*)
   .settings(betterConsole)
 
 lazy val coreAlpha =
   Project("spawning-pool-core-alpha", file("spawning-pool-core-alpha"))
-    .settings(commonSettings*)
     .settings(fs2*)
     .settings(specs2*)
     .settings(betterConsole)
 
 lazy val coreCats =
   Project("spawning-pool-scalaz", file("spawning-pool-scalaz"))
-    .settings(commonSettings*)
     .dependsOn(coreAlpha)
 
 lazy val benchmark = project
-  .settings(commonSettings*)
   .dependsOn(core)
 
 lazy val storage =
@@ -33,7 +22,6 @@ lazy val storage =
     .withYaml
 
 lazy val root = Project("spawning-pool", file("."))
-  .settings(commonSettings*)
   .aggregate(core, benchmark, coreAlpha, storage)
 
 publishArtifact := false

project/CrossPublish2And3Plugin.scala

@@ -0,0 +1,17 @@
+import sbt.Keys.*
+import sbt.*
+
+/**
+  * Automatically enriches projects with the following settings (despite the word "override").
+  */
+object CrossPublish2And3Plugin extends AutoPlugin {
+
+  /**
+    * Thus plug-in will automatically be enabled; it has no requirements.
+    */
+  override def trigger: PluginTrigger = AllRequirements
+
+  override val buildSettings: Seq[Setting[?]] = Seq(
+    crossScalaVersions := Seq("2.13.18")
+  )
+}

project/ProjectPlugin.scala

@@ -16,6 +16,10 @@ object ProjectPlugin extends AutoPlugin {
     */
   override def trigger: PluginTrigger = AllRequirements
 
+  override val buildSettings: Seq[Setting[?]] = Seq(
+    organization := "com.htmlism"
+  )
+
   object ThingsToAutoImport {
     private def jarName(s: String) =
       "spawning-pool-" + s

project/Scala2Plugin.scala

@@ -0,0 +1,31 @@
+import sbt.Keys.*
+import sbt.*
+
+/**
+  * Automatically enriches projects with the following settings (despite the word "override").
+  */
+object Scala2Plugin extends AutoPlugin {
+
+  /**
+    * Thus plug-in will automatically be enabled; it has no requirements.
+    */
+  override def trigger: PluginTrigger = AllRequirements
+
+  override val buildSettings: Seq[Setting[?]] = Seq(
+    scalaVersion := "2.13.18"
+  )
+
+  // putting into project settings helps with late binding for properly detecting scala3 cross build
+  override val projectSettings: Seq[Setting[?]] = Seq(
+    scalacOptions ++= scala3Syntax(scalaVersion.value)
+  )
+
+  private def scala3Syntax(s: String) =
+    CrossVersion.partialVersion(s) match {
+      case Some((2, _)) =>
+        Seq("-Xsource:3")
+
+      case _ =>
+        Nil
+    }
+}