How to resolve: "resolving package versions" in Julia? - julia

Question

I am new to the programming language Julia. I ran a few mixed models using the MixedModels package. Then, i wanted to run some average marginal effects using the Effects package. However, i get an error (see below).
To solve this issue, i tried to update all packages by using Pkg.update(). Then, i tried to install a particular version of the Effects package by using Pkg.rm("Effects") Pkg.add("Effects", v"0.1.4"). However, none of these options solved the issue. Could someone point out to me please what am i doing wrong?
Pkg.add("Effects")
Resolving package versions...
Unsatisfiable requirements detected for package Effects [8f03c58b]:
Effects [8f03c58b] log:
├─possible versions are: 0.1.0-0.1.4 or uninstalled
├─restricted to versions * by an explicit requirement, leaving only versions 0.1.0-0.1.4
└─restricted by julia compatibility requirements to versions: uninstalled — no versions left
Stacktrace:
[1] propagate_constraints!(::Pkg.Resolve.Graph, ::Set{Int64}; log_events::Bool) at /Users/julia/buildbot/worker/package_macos64/build/usr/share/julia/stdlib/v1.5/Pkg/src/Resolve/graphtype.jl:1005
[2] propagate_constraints! at /Users/julia/buildbot/worker/package_macos64/build/usr/share/julia/stdlib/v1.5/Pkg/src/Resolve/graphtype.jl:946 [inlined] (repeats 2 times)
[3] simplify_graph!(::Pkg.Resolve.Graph, ::Set{Int64}; clean_graph::Bool) at /Users/julia/buildbot/worker/package_macos64/build/usr/share/julia/stdlib/v1.5/Pkg/src/Resolve/graphtype.jl:1460
[4] simplify_graph! at /Users/julia/buildbot/worker/package_macos64/build/usr/share/julia/stdlib/v1.5/Pkg/src/Resolve/graphtype.jl:1460 [inlined] (repeats 2 times)
[5] resolve_versions!(::Pkg.Types.Context, ::Array{Pkg.Types.PackageSpec,1}) at /Users/julia/buildbot/worker/package_macos64/build/usr/share/julia/stdlib/v1.5/Pkg/src/Operations.jl:375
[6] targeted_resolve at /Users/julia/buildbot/worker/package_macos64/build/usr/share/julia/stdlib/v1.5/Pkg/src/Operations.jl:1114 [inlined]
[7] tiered_resolve(::Pkg.Types.Context, ::Array{Pkg.Types.PackageSpec,1}) at /Users/julia/buildbot/worker/package_macos64/build/usr/share/julia/stdlib/v1.5/Pkg/src/Operations.jl:1100
[8] _resolve at /Users/julia/buildbot/worker/package_macos64/build/usr/share/julia/stdlib/v1.5/Pkg/src/Operations.jl:1120 [inlined]
[9] add(::Pkg.Types.Context, ::Array{Pkg.Types.PackageSpec,1}, ::Array{Base.UUID,1}; preserve::Pkg.Types.PreserveLevel, platform::Pkg.BinaryPlatforms.MacOS) at /Users/julia/buildbot/worker/package_macos64/build/usr/share/julia/stdlib/v1.5/Pkg/src/Operations.jl:1135
[10] add(::Pkg.Types.Context, ::Array{Pkg.Types.PackageSpec,1}; preserve::Pkg.Types.PreserveLevel, platform::Pkg.BinaryPlatforms.MacOS, kwargs::Base.Iterators.Pairs{Union{},Union{},Tuple{},NamedTuple{(),Tuple{}}}) at /Users/julia/buildbot/worker/package_macos64/build/usr/share/julia/stdlib/v1.5/Pkg/src/API.jl:188
[11] add(::Pkg.Types.Context, ::Array{Pkg.Types.PackageSpec,1}) at /Users/julia/buildbot/worker/package_macos64/build/usr/share/julia/stdlib/v1.5/Pkg/src/API.jl:139
[12] #add#21 at /Users/julia/buildbot/worker/package_macos64/build/usr/share/julia/stdlib/v1.5/Pkg/src/API.jl:67 [inlined]
[13] add at /Users/julia/buildbot/worker/package_macos64/build/usr/share/julia/stdlib/v1.5/Pkg/src/API.jl:67 [inlined]
[14] #add#20 at /Users/julia/buildbot/worker/package_macos64/build/usr/share/julia/stdlib/v1.5/Pkg/src/API.jl:66 [inlined]
[15] add at /Users/julia/buildbot/worker/package_macos64/build/usr/share/julia/stdlib/v1.5/Pkg/src/API.jl:66 [inlined]
[16] add(::String; kwargs::Base.Iterators.Pairs{Union{},Union{},Tuple{},NamedTuple{(),Tuple{}}}) at /Users/julia/buildbot/worker/package_macos64/build/usr/share/julia/stdlib/v1.5/Pkg/src/API.jl:65
[17] add(::String) at /Users/julia/buildbot/worker/package_macos64/build/usr/share/julia/stdlib/v1.5/Pkg/src/API.jl:65
[18] top-level scope at In[216]:1
[19] include_string(::Function, ::Module, ::String, ::String) at ./loading.jl:1091

Answer 1

It looks like you are using Julia version 1.5, but all existing versions of the Effects package require at least Julia version 1.6 (see Effects/Compat.toml). If you can, you should upgrade Julia to 1.6 since that is (at the time of writing) the supported stable version.
To explain the error message a bit:
Effects [8f03c58b] log:
├─possible versions are: 0.1.0-0.1.4 or uninstalled
├─restricted to versions * by an explicit requirement, leaving only versions 0.1.0-0.1.4
└─restricted by julia compatibility requirements to versions: uninstalled — no versions left
The resolver starts with all existing versions as options (0.1.0-0.1.4) including the option to not have the package installed at all (uninstalled).
The second line filters out the uninstalled option since you are requesting it to be installed (explicit requirement). * is a version wildcard which just means that you have not requested a specific version to be installed.
The third line is then causing the error, due to requirements on the Julia version all the remaining options are filtered out and you get no versions left, i.e. no more remaining options.