Merge pull request #6310 from eed3si9n/wip/warn_version_scheme

Warn on missing versionScheme

main/src/main/scala/sbt/Defaults.scala

@@ -3045,6 +3045,14 @@ object Classpaths {
       )
     },
     publishConfiguration := {
+      val s = streams.value
+      val vs = versionScheme.value
+      if (vs.isEmpty)
+        s.log.warn(
+          s"""versionScheme setting is empty; set `ThisBuild / versionScheme := Some("early-semver")` or `Some("pvp")`
+             |so tooling can use it for evction errors etc - https://www.scala-sbt.org/1.x/docs/Publishing.html""".stripMargin
+        )
+      else ()
       publishConfig(
         publishMavenStyle.value,
         deliverPattern(crossTarget.value),