[Nix-dev] JAVA_HOME and other environment variables

[Svein Ove Aas]

Context: https://github.com/NixOS/nixpkgs/issues/13653

There are a few packages which can't be considered properly installed (and
usable) without setting environment variables, this example being the Java
development kit.

Some Java-based tools need to know where to find the JDK. The way they do
this is by looking at the JAVA_HOME environment variable. That is...
currently, it isn't set at all, unless you use nix-shell or an equivalent
mechanism.

I've thought of a couple of solutions, but would welcome other suggestions.
In no particular order...

(The problem is not restricted to just JAVA_HOME.)

- Wrapping the the JDK binaries with makeWrapper.
  This is a non-starter, as it's common to use JAVA_HOME in scripts.

- JAVA_HOME is set in the JDK's setup-hook. We can source that file on
shell startup.
  This works well for nix-shell, and is the approach I've chosen to take
globally for a temporary fix. Unfortunately, it is in a sense even worse
than the status quo. Since this produces a pointer into /nix/store, the
value of JAVA_HOME in a running shell can become invalid because the JDK in
question is GC'd (!), or superseded by a newer one *without* being deleted
(!!).

- Adding another directory under /run, containing symlinks that we can
mutate.
  Has the obvious problem of impurity, but we're talking about system (or
user) profiles; they're already impure, in the same sense. I don't see any
technical issues here, but that doesn't mean there aren't any. I'm not sure
how to implement it, or even whether I should.
  We'd have "JAVA_HOME=/run/env/JAVA_HOME", or so.

One further concern...

- Right now, the only way to install Java system-wide is to put it in
environment.systemPackages. Or using nix-env. Either way, JAVA_HOME
wouldn't get set; this is true even with that PR. I've been trying to think
of ways to fix this, but I have no idea how. Send help!
  As a result, even if I add programs.java to NixOS, it doesn't help anyone
who's got the problem right now.

....

I'd like to implement a general solution for all such situations, ideally
one that would get merged. Rant over, though. Thoughts?
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://lists.science.uu.nl/pipermail/nix-dev/attachments/20160305/1cda5e5d/attachment.html