[Nix-dev] JAVA_HOME and other environment variables

[Svein Ove Aas]

That's effectively what happens already, if you use nix-shell.

I'm concerned mostly about users who don't know to do that. Someone trying
to run a script from a different brand of unix, for example.

In theory, if there is a java binary on the PATH, there should also be a
JAVA_HOME. That's Oracle's take on this, but... well, I prefer Nix to have
as few surprises as possible.

On Sun, Mar 6, 2016 at 8:12 PM zimbatm <zimbatm at zimbatm.com> wrote:

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 question is GC'd (!), or superseded by a newer one *without* being deleted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