Fixed sbt bootstrap startup

bin/compile

@@ -13,7 +13,8 @@ OPT_DIR=$BP_DIR/opt
 APP_BUILD_DIR=$(cd $1; pwd)
 CACHE_DIR=$2
 
-BUILD_DIR="/tmp/build_dir"
+# Move app to a static build dir to keep paths the same between builds
+BUILD_DIR="/tmp/scala_buildpack_build_dir"
 mv $APP_BUILD_DIR $BUILD_DIR
 
 curl --silent --location http://heroku-jvm-common.s3.amazonaws.com/jvm-buildpack-common.tar.gz | tar xz
@@ -47,7 +48,7 @@ SBT_BINDIR="$SBT_USER_HOME"/bin
 cd $BUILD_DIR
 
 # unpack cache
-CACHED_DIRS="$SBT_USER_HOME/.ivy2 $SBT_BINDIR target project/target"
+CACHED_DIRS="$SBT_USER_HOME/.ivy2 $SBT_BINDIR target project/target project/boot"
 for DIR in $CACHED_DIRS; do
   cache_copy $DIR $CACHE_DIR $BUILD_DIR
 done
@@ -87,8 +88,9 @@ if [ ! -f "$SBT_BINDIR"/"$SBT_JAR" ]; then
   ## clean up any old versions
   /bin/rm -f sbt sbt-launch-*.jar || true
 
-  echo "-----> Building app with sbt"
+  echo -n "-----> Downloading SBT..."
   curl --silent --max-time 60 -O --location $SBT_URL --fail || error "Failed to download $SBT_JAR"
+  echo "done"
 
   echo "#!/usr/bin/env bash" > sbt
   echo "/usr/bin/java -Dsbt.boot.properties=/app/.sbt_home/bin/sbt.boot.properties  -Duser.home=/app/.sbt_home -Divy.default.ivy.user.dir=/app/.sbt_home/.ivy2 -jar /app/.sbt_home/bin/$SBT_JAR \"\$@\"" >> sbt
@@ -111,7 +113,7 @@ cp -p $OPT_DIR/$HEROKU_PLUGIN $SBT_USER_HOME/.sbt/plugins/$HEROKU_PLUGIN
 # build app
 echo "-----> Running: sbt $SBT_TASKS"
 test -e "$SBT_BINDIR"/sbt.boot.properties && PROPS_OPTION="-Dsbt.boot.properties=$SBT_BINDIR/sbt.boot.properties"
-HOME="$SBT_USER_HOME_ABSOLUTE" java -Xms768M -Xmx1024M -XX:MaxPermSize=512M -XX:+CMSClassUnloadingEnabled -Dfile.encoding=UTF8 -Duser.home="$SBT_USER_HOME_ABSOLUTE" -Dsbt.log.noformat=true -Divy.default.ivy.user.dir="$SBT_USER_HOME_ABSOLUTE/.ivy2" -Dsbt.global.base=$SBT_USER_HOME_ABSOLUTE $PROPS_OPTION -jar "$SBT_BINDIR"/$SBT_JAR compile 2>&1 | sed -u 's/^/       /'
+HOME="$SBT_USER_HOME_ABSOLUTE" java -Xms768M -Xmx1024M -XX:MaxPermSize=512M -XX:+CMSClassUnloadingEnabled -Dfile.encoding=UTF8 -Duser.home="$SBT_USER_HOME_ABSOLUTE" -Dsbt.log.noformat=true -Divy.default.ivy.user.dir="$SBT_USER_HOME_ABSOLUTE/.ivy2" -Dsbt.global.base="$SBT_USER_HOME_ABSOLUTE" $PROPS_OPTION -jar "$SBT_BINDIR"/$SBT_JAR $SBT_TASKS 2>&1 | sed -u 's/^/       /'
 if [ "${PIPESTATUS[*]}" != "0 0" ]; then
   echo " !     Failed to build app with sbt"
   exit 1
@@ -145,4 +147,5 @@ if is_play $BUILD_DIR ; then
   fi
 fi
 
+# Move compiled app back to where Heroku expects it
 mv $BUILD_DIR $APP_BUILD_DIR