Title: Spark Overlay Revival
Author: Yuan Liao <liaoyuan@gmail.com>
Posted: 2021-08-01
Revision: 3
News-Item-Format: 2.0

Most of the ebuilds in ::spark-overlay have now been restored to a
working state after a batch of Java package clean-ups in ::gentoo
throughout the past months that had removed various dependencies of
packages in this overlay.  In particular, the Apache Spark core package,
dev-java/spark-core, can be installed on systems with a recent copy of
::gentoo again.

In addition, ::spark-overlay now houses a new experimental
infrastructure supporting the Kotlin programming language on Gentoo.  It
offers:

- Kotlin core library packages that can be built from source
  (dev-java/kotlin-stdlib, dev-java/kotlin-stdlib-jdk8,
  dev-java/kotlin-test-junit, dev-java/kotlin-reflect, etc.)

- Newer versions of the Kotlin compiler that can be installed in
  parallel with each other (dev-lang/kotlin-bin:1.4,
  dev-lang/kotlin-bin:1.5)

- An eselect module for choosing the Kotlin compiler version to use
  (app-eselect/eselect-kotlin)

- A set of eclasses useful for creating Kotlin packages (kotlin.eclass,
  kotlin-utils.eclass)

Users who have already installed dev-java/spark-core on their system
from an old copy of ::spark-overlay should be able to upgrade packages
in this overlay without uninstalling them.  However, due to the new
Kotlin support infrastructure, packages in this overlay that use Kotlin
(dev-java/okhttp, dev-java/okio and dev-java/reactor-core) require
installation of the new Kotlin packages for Kotlin 1.4 before they can
be upgraded.

The following command can be used to install Kotlin 1.4, and it is
applicable to both old and new users of ::spark-overlay:

    emerge -a dev-lang/kotlin-bin:1.4

This is sufficient for a Kotlin 1.4 installation based on the binary
JARs built and provided by the upstream for kotlin-stdlib and
kotlin-reflect.  Users who wish to build these libraries from source
should run an additional command after those ones above:

    emerge -a1 dev-java/kotlin-{stdlib,reflect}:1.4

Before this batch of updates to ebuilds in ::spark-overlay, some
packages in this overlay required their 'binary' USE flag to be
explicitly enabled.  This is no longer the case: many of those packages
can now be built from source, and the remaining packages that still
cannot be compiled from source are having their 'binary' USE flag
enabled by default.  This means that users of this overlay do not need
to add the USE flag settings in pkgs-need-binary.txt under the root of
this overlay's tree to /etc/portage/package.use anymore.

For more information about the new Kotlin packages, please consult a
relevant page on Gentoo Wiki:

    https://wiki.gentoo.org/wiki/Kotlin

Should any issue that prevents the packages from being upgraded arise,
please uninstall all packages from ::spark-overlay and then reinstall
them.