redo how crossScalaVersions works

.travis.yml

@@ -2,10 +2,9 @@ language: scala
 
 env:
   global:
-    - PUBLISH_JDK=openjdk8 # admin/build.sh only publishes when running on this jdk
-# Don't commit sensitive files, instead commit a version encrypted with $SECRET,
-# this environment variable is encrypted with this repo's private key and stored below:
-# (See http://docs.travis-ci.com/user/environment-variables/#Secure-Variables.)
+      # Don't commit sensitive files, instead commit a version encrypted with $SECRET,
+      # this environment variable is encrypted with this repo's private key and stored below:
+      # (See http://docs.travis-ci.com/user/environment-variables/#Secure-Variables.)
     - secure: "apmuVagS7WgWzg9HeDLCcX4INxazi50qukOfPkvluJjm58RCJsDwaZseXrQGqyPzRKuBnAetJ4NDWbZMRkm6QpTiH8grPwDl6iNUSVivvzOZGl3Iy8LvNxUv6CYoQBG+R7d8dW//1xcoHtT2zYo3dYEFpSelfNMMLADNUKXSQmI="
 
 before_install:
@@ -14,16 +13,9 @@ before_install:
   - sudo mv /tmp/hosts /etc/hosts
 script:
   - admin/build.sh
-scala:
-  - 2.11.8
-  - 2.12.0-RC1
 jdk:
   - openjdk6
   - oraclejdk8
-matrix:
-  exclude:
-    - scala: 2.12.0-RC1
-      jdk: openjdk6
 notifications:
   email:
     - [email protected]

admin/build.sh

@@ -5,16 +5,16 @@
 # git on travis does not fetch tags, but we have TRAVIS_TAG
 # headTag=$(git describe --exact-match ||:)
 
-if [ "$TRAVIS_JDK_VERSION" == "$PUBLISH_JDK" ] && [[ "$TRAVIS_TAG" =~ ^v[0-9]+\.[0-9]+\.[0-9]+(-[A-Za-z0-9-]+)? ]]; then
+if [[ "$TRAVIS_TAG" =~ ^v[0-9]+\.[0-9]+\.[0-9]+(-[A-Za-z0-9-]+)? ]]; then
   echo "Going to release from tag $TRAVIS_TAG!"
   myVer=$(echo $TRAVIS_TAG | sed -e s/^v//)
   publishVersion='set every version := "'$myVer'"'
-  extraTarget="publish-signed"
+  extraTarget="+publish-signed"
 
   cat admin/gpg.sbt >> project/plugins.sbt
   admin/decrypt.sh sensitive.sbt
   (cd admin/ && ./decrypt.sh secring.asc)
 fi
 
 # the concurrentRestrictions should prevent spurious test failures, see https://github.com/spray/spray/pull/233
-sbt ++$TRAVIS_SCALA_VERSION 'set concurrentRestrictions in Global += Tags.limit(Tags.Test, 1)' "$publishVersion" clean update compile test $extraTarget
+sbt "$publishVersion" clean update +compile +test +publishLocal $extraTarget

build.sbt

@@ -8,8 +8,16 @@ lazy val commonSettings = scalaModuleSettings ++ Seq(
   repoName                   := "scala-continuations",
   organization               := "org.scala-lang.plugins",
   version                    := "1.0.3-SNAPSHOT",
-  scalaVersion               := "2.11.8",
-  crossScalaVersions         := Seq("2.11.8", "2.12.0-RC1"),
+  scalaVersion               := crossScalaVersions.value.head,
+  crossScalaVersions         := {
+    val java = System.getProperty("java.version")
+    if (java.startsWith("1.6.") || java.startsWith("1.7."))
+      Seq("2.11.8")
+    else if (java.startsWith("1.8.") || java.startsWith("1.9."))
+      Seq("2.12.0-RC1")
+    else
+      sys.error(s"don't know what Scala versions to build on $java")
+  },
   snapshotScalaBinaryVersion := "2.11.8",
   scalacOptions ++= Seq(
     "-deprecation",