Insert version in the right place in add-version workflow

Author: kubukoz

.github/workflows/add-version.yml

@@ -69,7 +69,7 @@ jobs:
       - name: Commit new version support
         run: |
           gpg --list-keys
-          echo "${{inputs.scala_version}}" >> scala-versions
+          sbt "addVersion ${{inputs.scala_version}}"
           sbt "generateAll;++${{inputs.scala_version}} test"
           git add --all
           git commit -m "Add ${{inputs.scala_version}} support"

build.sbt

@@ -99,3 +99,4 @@ val betterToString =
     .aggregate(plugin, tests)
     .enablePlugins(NoPublishPlugin)
     .enablePlugins(ReadmePlugin)
+    .enablePlugins(AddVersionPlugin)

project/AddVersionPlugin.scala

@@ -0,0 +1,60 @@
+import sbt.AutoPlugin
+
+import sbt.Def
+import sbt._
+
+object AddVersionPlugin extends AutoPlugin {
+
+  val addVersion = inputKey[Unit]("Write the given version to scala-versions")
+
+  case class ParsedVersion(mainPart: String, rcPart: Option[String]) {
+
+    def render: String =
+      rcPart match {
+        case Some(rc) => s"$mainPart-$rc"
+        case None     => mainPart
+      }
+
+  }
+
+  object ParsedVersion {
+
+    // if mainPart is the same, RCs go first
+    implicit val ordering: Ordering[ParsedVersion] = Ordering.by { v =>
+      (
+        v.mainPart,
+        v.rcPart match {
+          case Some(rc) => s"0$rc" // prepend 0 to RCs to sort them before non-RCs
+          case None     => "1" // non-RCs come after RCs
+        }
+      )
+    }
+
+    def parse(version: String): ParsedVersion = {
+      val parts = version.split("-")
+      val mainPart = parts.head
+      val rcPart = if (parts.length > 1) Some(parts(1)) else None
+      ParsedVersion(mainPart, rcPart)
+    }
+
+  }
+
+  override def projectSettings: Seq[Def.Setting[_]] = Seq(
+    addVersion := {
+      // Read the version from the input
+      val version = Def.spaceDelimited("<version>").parsed.mkString(" ")
+
+      val path = file("scala-versions")
+      val currentVersions = IO
+        .read(path)
+        .split("\n")
+        .map(_.trim)
+        .filterNot(_.isEmpty)
+        .toSet
+
+      val newVersions = (currentVersions + version).toSeq.map(ParsedVersion.parse).sorted.map(_.render)
+      IO.write(path, newVersions.mkString("\n") + "\n")
+    }
+  )
+
+}