Documentation claims Bazel requires JDK8

[katre]

Currently the install documents (at https://docs.bazel.build/versions/master/install-compile-source.html#bootstrap-unix-prereq) claim that Bazel works with JDK8, but this is no longer accurate. We need to update the docs to correctly explain the required JDK versions.

[cushon]

@lberki

It depends what "works with" means (--server_javabase, --host_javabase, or --javabase)? Have we decided which JDK versions are supported yet?

Those docs are talking about bootstrapping, and JDK 8 is probably still a fine choice for that. The issue in #6550 only affects the binaries without an embedded JDK.

[meisterT]

@katre I just followed the steps in a docker container and it produced a working bazel binary.

[katre]

@meisterT Was that comment supposed to be on a different issue?

[meisterT]

No, the comment was meant to be on this issue. However, in the meantime I was made aware that while the bootstrap succeeds and the resulting binary can build C++, it cannot build Java.

Assigning to @lberki to clarify supported Java version before we spend any time here.

cc @iirina

[lberki]

Regrettably, bootstrapping does not work with JDK 9, at least on Ubuntu 16.04 and Bazel 0.18 (I just checked). So the instructions are indeed accurate.

[lberki]

My bad -- actually, it does, except with 16.04 has a bug that makes openjdk-9-jdk not install correctly :(

[baryluk]

In bootstraping doc, I also found that it uses openjdk-8-jdk package as an example, but I think it is better to use default-jdk-headless (Debian/Ubuntu) , and if needed it will install newer JDK. User will still need to verify it is at least JDK 8 or 9.

[ash2k]

Contributing to Bazel page also needs to mention which JDK is needed. I had version 11 installed and tests were failing. I assumed that JDK is needed because Bazel prints that it couldn't find any JDK matching 1.8 requirement or something like that and tried it. It also didn't work. I gave up. Then I have accidentally discovered that JDK 9 is what is needed to test/build bazel and it worked. Very confusing experience. It was my very first bazel PR.

[Flamefire]

Related issue: #6035

So:

It depends what "works with" means

The docu states clearly "JDK 8. You must install version 8 of the JDK. Versions other than 8 are not supported." but #6035 states that "--host_javabase= won't work anymore."

Especially building Bazel on Power9 is a PITA due to the Java dependency.

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