Why does worker throw error when importing local package on master process?

General Usage
1

If I add processes after importing a local package, things work as expected:

julia> using Pkg
julia> Pkg.activate(".")
  Activating environment at `~/MyPackage/Project.toml`
julia> using Distributed
julia>
julia> using MyPackage # must import MyPackage first
julia> addprocs(1)
1-element Vector{Int64}:
 2

If I import after adding processes, then I get an unexpected error:

julia> using Pkg
julia> Pkg.activate(".")
  Activating environment at `~/MyPackage/Project.toml`
julia> using Distributed
julia>
julia> addprocs(1)
julia> using MyPackage
**ERROR:** On worker 2:
ArgumentError: Package QuantumCircuits [01625e0c-f410-4aff-9d33-8c5e8b164a60] is required but does not seem to be installed:
 - Run `Pkg.instantiate()` to install all recorded dependencies.

Why is worker 2 throwing an error? I haven’t imported MyPackage on worker 2. I’d expect to be able to activate the project environment before trying to import on the worker.

julia> versioninfo()
Julia Version 1.6.1
Commit 6aaedecc44 (2021-04-23 05:59 UTC)
Platform Info:
  OS: macOS (x86_64-apple-darwin18.7.0)
  CPU: Apple M1
  WORD_SIZE: 64
  LIBM: libopenlibm
  LLVM: libLLVM-11.0.1 (ORCJIT, westmere)
2

Packages are loaded (but not brought into scope) on all workers.

3

Perhaps it has to go like this:

julia> using Distributed

julia> addprocs(2)
2-element Vector{Int64}:
 2
 3

julia> @everywhere using Pkg

julia> @everywhere Pkg.activate(".")
  Activating  Activating  Activating   new environment at `C:\WINDOWS\system32\Project.toml`new environment at `C:\WINDOWS\system32\Project.toml`
new environment at `C:\WINDOWS\system32\Project.toml`

Can you check if

@everywhere using MyPackage

now works?

4

Hm why? This might make sense if the workers shared the same environment as the master process, but they don’t.