[Nix-dev] JAVA_HOME and other environment variables

[zimbatm]

What if the JRE(s) also included a `java-env.sh` that can be sourced ? Then
it's easy to build wrappers that source it dynamically.

On Sat, 5 Mar 2016 at 17:34 Svein Ove Aas <sveina at gmail.com> wrote:

> 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 question is GC'd (!), or superseded by a newer one *without* being deleted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?
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