Generate changelog during release

Author: muuki88

build.sbt

@@ -74,6 +74,8 @@ releaseProcess := Seq[ReleaseStep](
   setReleaseVersion,
   commitReleaseVersion,
   tagRelease,
+  generateReleaseChangelog,
+  commitChangelog,
   releaseStepCommandAndRemaining("^ publishSigned"),
   setNextVersion,
   commitNextVersion,

project/ChangelogPlugin.scala

@@ -0,0 +1,145 @@
+import sbt._
+import sbt.Keys._
+import sbt.complete._
+import sbt.complete.DefaultParsers._
+import sbtrelease.ReleasePlugin.autoImport._
+import sbtrelease.{ReleasePlugin, Vcs}
+
+import scala.sys.process._
+
+/**
+  * == Changelog Plugin ==
+  *
+  * This plugins manages the `CHANGELOG.md` file via the `github_changelog_generator` tool.
+  * Make sure to follow the instructions on the project page and `github_changelog_generator`
+  * is available.
+  *
+  * You will also need a Github token during the release process. `github_changelog_generator`
+  * supports environment files or username/password combinations, but at this point the ChangelogPlugin
+  * doesn't support them. The plugin also relies on the sensible defaults from `github_changelog_generator`,
+  * which means
+  * - the project name and organization are picked up automatically
+  * - the output file is named CHANGELOG.md
+  * - the changelog file includes everything (issues, pull requests)
+  * - generated for all available version tasks
+  * - runs in verbose mode
+  *
+  * @see [[https://github.com/skywinder/github-changelog-generator]]
+  * @see [[https://github.com/skywinder/github-changelog-generator/wiki/Advanced-change-log-generation-examples]]
+  */
+object ChangelogPlugin extends AutoPlugin {
+
+  override def requires: Plugins = ReleasePlugin
+
+  override def trigger = AllRequirements
+
+  object autoImport {
+
+    /**
+      * Generates the changelog during a release
+      */
+    val generateReleaseChangelog = ReleaseStep(generateChangelogStep)
+
+    /**
+      * Commits the generated changelog.
+      */
+    val commitChangelog = ReleaseStep(commitChangelogStep)
+
+    /**
+      * Task that executes the `github_changelog_generator`.
+      */
+    val generateChangelog: InputKey[Unit] =
+      inputKey[Unit]("executes the github_changelog_generator to update the CHANGELOG.MD")
+
+    /**
+      * Github token used for the changelog generation
+      */
+    val generateChangelogToken: SettingKey[Option[String]] =
+      settingKey[Option[String]]("github token used for the changelog generation")
+  }
+
+  import autoImport._
+
+  private case class GithubChangeLogParameters(token: String)
+
+  private val githubChangeLogParser: Parser[GithubChangeLogParameters] = {
+    (Space ~ token("--token") ~ Space ~> StringBasic).map(GithubChangeLogParameters)
+  }
+
+  override def projectSettings: Seq[Setting[_]] =
+    Seq(generateChangelogToken := None, generateChangelog := {
+      val log = streams.value.log
+      val parameters = githubChangeLogParser.parsed
+      Seq("github_changelog_generator", "--token", parameters.token) ! log match {
+        case 0 => log.success("CHANGELOG.md updated successfully")
+        case n => sys.error(s"Failed updating CHANGELOG.md. Process existed with status code $n")
+      }
+    })
+
+  private def generateChangelogStep(state: State): State = {
+    val extracted = Project.extract(state)
+    val predefinedToken = extracted.get(generateChangelogToken)
+
+    val githubToken = readToken(predefinedToken)
+
+    val (newState, _) = extracted.runInputTask(generateChangelog, s" --token $githubToken", state)
+    newState
+  }
+
+  private def commitChangelogStep(state: State): State = {
+    val log = toProcessLogger(state)
+    val base = vcs(state).baseDir
+    val sign = Project.extract(state).get(releaseVcsSign)
+    val changelogFile = base / "CHANGELOG.md"
+
+    val relativePath = IO
+      .relativize(base, changelogFile)
+      .getOrElse(
+        "Version file [%s] is outside of this VCS repository with base directory [%s]!" format (changelogFile, base)
+      )
+
+    vcs(state).add(relativePath) !! log
+    val vcsAddOutput = (vcs(state).status !!).trim
+    if (vcsAddOutput.isEmpty) {
+      state.log.info("CHANGELOG.md hasn't been changed.")
+    } else {
+      vcs(state).commit("Update changelog", sign) ! log
+    }
+
+    state
+  }
+
+  /**
+    * Extracts the used vcs.
+    *
+    * Copied from the sbt-release plugin.
+    * @param state sbt state
+    * @return vcs implementation
+    */
+  private def vcs(state: State): Vcs =
+    Project
+      .extract(state)
+      .get(releaseVcs)
+      .getOrElse(sys.error("Aborting release. Working directory is not a repository of a recognized VCS."))
+
+  /**
+    * Creates a ProcessLogger from the current sbt state.
+    *
+    * Copied from the sbt-release plugin.
+    * @param state
+    * @return a process logger
+    */
+  private def toProcessLogger(state: State): ProcessLogger = new ProcessLogger {
+    override def err(s: => String): Unit = state.log.info(s)
+    override def out(s: => String): Unit = state.log.info(s)
+    override def buffer[T](f: => T): T = state.log.buffer(f)
+  }
+
+  private def readToken(predefinedToken: Option[String]): String =
+    predefinedToken.getOrElse(SimpleReader.readLine("Github token: ") match {
+      case Some(input) if input.trim.isEmpty => sys.error("No token provided")
+      case Some(input)                       => input
+      case None                              => sys.error("No token provided")
+    })
+
+}