Update readme during relaese

build.sbt

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

project/ReadmeReleasePlugin.scala

@@ -0,0 +1,105 @@
+import sbt._
+import sbt.Keys._
+import sbt.complete._
+import sbt.complete.DefaultParsers._
+import sbtrelease.ReleasePlugin.autoImport._
+import sbtrelease.{ReleasePlugin, Vcs}
+
+import scala.sys.process._
+
+/**
+  * == ReadmeRelease Plugin ==
+  * 
+  * Changes the version in the README.md during a release.
+  * 
+  */
+object ReadmeReleasePlugin extends AutoPlugin {
+
+  override def requires: Plugins = ReleasePlugin
+
+  override def trigger = AllRequirements
+
+  object autoImport {
+
+    /**
+      * Update the readme file during a release
+      */
+    val updateReadme = ReleaseStep(updateReadmeStep)
+
+    /**
+      * Commits the readme changes.
+      */
+    val commitReadme = ReleaseStep(commitReadmeStep)
+
+  }
+
+
+  private def updateReadmeStep(state: State): State = {
+    val extracted = Project.extract(state)
+    val releaseVersion = extracted.get(version)
+    val base = extracted.get(baseDirectory)
+    val readmeFile = base / "README.md"
+
+    val versionRegex = """(\d{1,2}\.\d{1,2}\.\d{1,2})""".r
+    val updatedReadmeContent = versionRegex.replaceAllIn(
+      IO.read(readmeFile),
+      releaseVersion
+    )
+
+    IO.write(readmeFile, updatedReadmeContent)
+
+
+    state
+  }
+
+  private def commitReadmeStep(state: State): State = {
+    val log = toProcessLogger(state)
+    val base = vcs(state).baseDir
+    val sign = Project.extract(state).get(releaseVcsSign)
+    val readmeFile = base / "README.md"
+
+    val relativePath = IO
+      .relativize(base, readmeFile)
+      .getOrElse(
+        "Version file [%s] is outside of this VCS repository with base directory [%s]!" format (readmeFile, base)
+      )
+
+    vcs(state).add(relativePath) !! log
+    val vcsAddOutput = (vcs(state).status !!).trim
+    if (vcsAddOutput.isEmpty) {
+      state.log.info("README.md hasn't been changed.")
+    } else {
+      vcs(state).commit("Update release version in readme", 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)
+  }
+
+
+}