Propagate package environment to local workers

[fredrikekre]

Propagate package environment to local workers, fixes #28781, closes #42089.

[fonsp]

About the NEWS.md update, it looks like the ENV variables JULIA_LOAD_PATH and JULIA_DEPOT_PATH were already propagated in previous Julia versions:

Tests on Julia 1.8

LOAD_PATH

➜  Downloads JULIA_LOAD_PATH="$(pwd)/hello:$JULIA_LOAD_PATH" julia 
               _
   _       _ _(_)_     |  Documentation: https://docs.julialang.org
  (_)     | (_) (_)    |
   _ _   _| |_  __ _   |  Type "?" for help, "]?" for Pkg help.
  | | | | | | |/ _` |  |
  | | |_| | | | (_| |  |  Version 1.8.3 (2022-11-14)
 _/ |\__'_|_|_|\__'_|  |  Official https://julialang.org/ release
|__/                   |

julia> LOAD_PATH
4-element Vector{String}:
 "/Users/fons/Downloads/hello"
 "@"
 "@v#.#"
 "@stdlib"

julia> import Distributed

julia> Distributed.addprocs(1)
1-element Vector{Int64}:
 2

julia> Distributed.remotecall_eval(Main, 2, :LOAD_PATH)
4-element Vector{String}:
 "/Users/fons/Downloads/hello"
 "@"
 "@v#.#"
 "@stdlib"

DEPOT_PATH

➜  Downloads JULIA_DEPOT_PATH="$(pwd)/hello" julia
               _
   _       _ _(_)_     |  Documentation: https://docs.julialang.org
  (_)     | (_) (_)    |
   _ _   _| |_  __ _   |  Type "?" for help, "]?" for Pkg help.
  | | | | | | |/ _` |  |
  | | |_| | | | (_| |  |  Version 1.8.3 (2022-11-14)
 _/ |\__'_|_|_|\__'_|  |  Official https://julialang.org/ release
|__/                   |

(@v1.8) pkg> st
  Installing known registries into `~/Downloads/hello`
Status `~/Downloads/hello/environments/v1.8/Project.toml` (empty project)

julia> import Distributed

julia> Distributed.addprocs(1)
1-element Vector{Int64}:
 2

julia> Distributed.remotecall_eval(Main, 2, :DEPOT_PATH)
1-element Vector{String}:
 "/Users/fons/Downloads/hello"

I believe this is because the entire ENV is propagated:

julia> Distributed.remotecall_eval(Main, 2, :ENV) == ENV
true

Perhaps the news entry can be reworded? The change is that the active project from the parent process is propagated, independently of how it was set (ENV variable, Pkg.activate, --project, ...). The DEPOT_PATH was already being propagated.

Suggested change: #48301