Implement back publishing support

**Problem**
For plugin code, like sbt plugins and Scala compiler plugin,
and even normal libraries, it's common for the maintainers to
want to back publish the current code base against a new version
of Scala (or sbt, Scala Nave etc) instead of bumping the version.

The current "bump the version" approach effectively pushes the work
of figuring out the correct patch version number to the end users.
In addition, if the plugin or the library does not cross publish
all variants, then the end user might need to figure out different
patch version to use effectively the same code.

**Solution**
This implements a mini DSL for tag `version[@command|@3.3.4][#comment]`,
which allows plugin authors to back publish a code base.

build.sbt

@@ -40,6 +40,7 @@ lazy val plugin = project
         case _      => "2.0.0-M2"
       }
     },
+    libraryDependencies += "org.scalameta" %% "munit" % "0.7.29" % Test,
     addSbtPlugin("com.github.sbt" % "sbt-dynver" % "5.1.0"),
     addSbtPlugin("com.github.sbt" % "sbt-git" % "2.1.0"),
     addSbtPlugin("com.github.sbt" % "sbt-pgp" % "2.3.0"),

plugin/src/main/scala/com/geirsson/CiReleasePlugin.scala

@@ -106,6 +106,8 @@ object CiReleasePlugin extends AutoPlugin {
       Some(s"scm:git:[email protected]:$user/$repo.git")
     )
 
+  lazy val cireleasePublishCommand = settingKey[String]("")
+
   override lazy val buildSettings: Seq[Def.Setting[_]] = List(
     dynverSonatypeSnapshots := true,
     scmInfo ~= {
@@ -128,15 +130,29 @@ object CiReleasePlugin extends AutoPlugin {
         } catch {
           case NonFatal(_) => None
         }
-    }
+    },
+    cireleasePublishCommand := {
+      val gitDescribe = dynverGitDescribeOutput.value
+      val v = gitDescribe.getVersion(
+        dynverCurrentDate.value,
+        dynverSeparator.value,
+        dynverSonatypeSnapshots.value
+      )
+      sys.env.get("CI_RELEASE") match {
+        case Some(cmd) => cmd
+        case None      => backPubVersionToCommand(v)
+      }
+    },
+    version ~= dropBackPubCommand,
   )
 
   override lazy val globalSettings: Seq[Def.Setting[_]] = List(
     (Test / publishArtifact) := false,
     publishMavenStyle := true,
     commands += Command.command("ci-release") { currentState =>
       val shouldDeployToSonatypeCentral = isDeploySetToSonatypeCentral(currentState)
-      val isSnapshot = isSnapshotVersion(currentState)
+      val version = getVersion(currentState)
+      val isSnapshot = isSnapshotVersion(version)
       if (!isSecure) {
         println("No access to secret variables, doing nothing")
         currentState
@@ -150,6 +166,8 @@ object CiReleasePlugin extends AutoPlugin {
         val reloadKeyFiles =
           "; set pgpSecretRing := pgpSecretRing.value; set pgpPublicRing := pgpPublicRing.value"
 
+        val publishCommand = getPublishCommand(currentState)
+
         if (shouldDeployToSonatypeCentral) {
           if (isSnapshot) {
             println(s"Sonatype Central does not accept snapshots, only official releases. Aborting release.")
@@ -161,7 +179,7 @@ object CiReleasePlugin extends AutoPlugin {
             println("Tag push detected, publishing a stable release")
             reloadKeyFiles ::
               sys.env.getOrElse("CI_CLEAN", "; clean ; sonatypeBundleClean") ::
-              sys.env.getOrElse("CI_RELEASE", "+publishSigned") ::
+              publishCommand ::
               sys.env.getOrElse("CI_SONATYPE_RELEASE", "sonatypeCentralRelease") ::
               currentState
           }
@@ -184,7 +202,7 @@ object CiReleasePlugin extends AutoPlugin {
             println("Tag push detected, publishing a stable release")
             reloadKeyFiles ::
               sys.env.getOrElse("CI_CLEAN", "; clean ; sonatypeBundleClean") ::
-              sys.env.getOrElse("CI_RELEASE", "+publishSigned") ::
+              publishCommand ::
               sys.env.getOrElse("CI_SONATYPE_RELEASE", "sonatypeBundleRelease") ::
               currentState
           }
@@ -210,10 +228,39 @@ object CiReleasePlugin extends AutoPlugin {
     }
   }
 
-  def isSnapshotVersion(state: State): Boolean = {
+  def getVersion(state: State): String =
     (ThisBuild / version).get(Project.extract(state).structure.data) match {
-      case Some(v) => v.endsWith("-SNAPSHOT")
+      case Some(v) => v
       case None    => throw new NoSuchFieldError("version")
     }
+
+  def getPublishCommand(state: State): String =
+    (ThisBuild / cireleasePublishCommand).get(Project.extract(state).structure.data) match {
+      case Some(v) => v
+      case None    => throw new NoSuchFieldError("cireleasePublishCommand")
+    }
+
+  def isSnapshotVersion(v: String): Boolean = v.endsWith("-SNAPSHOT")
+
+  def backPubVersionToCommand(ver: String): String =
+    if (ver.contains("@")) {
+      val afterAt = ver.split("@").drop(1).mkString("@")
+      val cmd =
+        if (afterAt.contains("#")) afterAt.split("#").head
+        else afterAt
+      if (cmd.isEmpty) sys.error(s"Invalid back-publish version: $ver")
+      else {
+        if (!cmd.head.isDigit) cmd
+        else if (cmd.contains(".x")) s";++${cmd};publishSigned"
+        else s";++${cmd}!;publishSigned"
+      }
+    } else "+publishSigned"
+
+  def dropBackPubCommand(ver: String): String = {
+    val nonComment =
+      if (ver.contains("#")) ver.split("#").head
+      else ver
+    if (nonComment.contains("@")) nonComment.split("@").head
+    else nonComment
   }
 }

plugin/src/test/scala/com/geirsson/CiReleaseTest.scala

@@ -0,0 +1,39 @@
+package com.geirsson
+
+import CiReleasePlugin.{ backPubVersionToCommand, dropBackPubCommand }
+
+class CiReleaseTest extends munit.FunSuite {
+  val expectedVer = "1.1.0"
+
+  test("Normal version default") {
+    assertEquals(backPubVersionToCommand("1.1.0"), "+publishSigned")
+    assertEquals(dropBackPubCommand("1.1.0"), expectedVer)
+  }
+
+  test("Command starting with number is assumed to be a cross version") {
+    assertEquals(backPubVersionToCommand("[email protected]"), ";++2.12.20!;publishSigned")
+    assertEquals(dropBackPubCommand("[email protected]"), expectedVer)
+
+    assertEquals(backPubVersionToCommand("[email protected]"), ";++3.x;publishSigned")
+    assertEquals(dropBackPubCommand("[email protected]"), expectedVer)
+  }
+
+  test("Non-number is treated as an alternative publish command") {
+    assertEquals(backPubVersionToCommand("1.1.0@foo/publishSigned"), "foo/publishSigned")
+    assertEquals(dropBackPubCommand("1.1.0@foo/publishSigned"), expectedVer)
+
+    assertEquals(backPubVersionToCommand("1.1.0@+foo/publishSigned"), "+foo/publishSigned")
+    assertEquals(dropBackPubCommand("1.1.0@+foo/publishSigned"), expectedVer)
+  }
+
+  test("Treat # as comments") {
+    assertEquals(backPubVersionToCommand("1.1.0#comment"), "+publishSigned")
+    assertEquals(dropBackPubCommand("1.1.0#comment"), expectedVer)
+
+    assertEquals(backPubVersionToCommand("[email protected]#comment"), ";++2.12.20!;publishSigned")
+    assertEquals(dropBackPubCommand("[email protected]#comment"), expectedVer)
+
+    assertEquals(backPubVersionToCommand("[email protected]#comment"), ";++3.x;publishSigned")
+    assertEquals(dropBackPubCommand("[email protected]#comment"), expectedVer)
+  }
+}