use JULIA_DEPOT_PATH as default install path

[Roger-luo]

fix #238

[MilesCranmer]

Quick comments:

1. Should use DEPOT_PATH rather than ENV[JULIA_DEPOT_PATH]. The global variable DEPOT_PATH is automatically populated in Julia and always exists.
2. Note that DEPOT_PATH is a vector of directories. I think it should go through them until it finds one that is writeable.

[Roger-luo]

Note that DEPOT_PATH is a vector of directories. I think it should go through them until it finds one that is writeable.

I'm not sure how to check if it's writable, it seems there is a filemode function but I didn't find any way of checking path permissions unless we want to do a shell call

[codecov]

Codecov Report

Patch coverage: 100.00% and no project coverage change.

Comparison is base (b3520ed) 82.84% compared to head (1c3089d) 82.84%.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #240   +/-   ##
=======================================
  Coverage   82.84%   82.84%           
=======================================
  Files          21       21           
  Lines        1586     1586           
=======================================
  Hits         1314     1314           
  Misses        272      272           

Impacted Files	Coverage Δ
src/configs.jl	76.92% <100.00%> (ø)

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[MilesCranmer]

I think first(DEPOT_PATH) as you wrote it is a good default strategy.

A more robust option, in case people have populated their JULIA_DEPOT_PATH with non-writeable directories (such as system-wide package registries), is to have path::Union{String,Nothing}=nothing. Then, if it's still nothing at the install step, you could loop through DEPOT_PATH, and wrap the writing in a try-catch. Once it succeeds writing you can exit the loop.

[Roger-luo]

Thanks I'm gonna do the simple fix.