Extensions do not load properly with --compiled-modules=no

[KristofferC]

Run julia with --compiled-modules=no and run:

julia> using Pkg; Pkg.activate(; temp=true); Pkg.add(["PGFPlotsX", "Colors"]); using PGFPlotsX; using Colors
 Activating new project at `/tmp/jl_SycxIQ`
    Updating registry at `~/.julia/registries/General`
    Updating git-repo `https://github.com/JuliaRegistries/General`
   Resolving package versions...
   Installed PGFPlotsX ─ v1.5.2
    Updating `/tmp/jl_SycxIQ/Project.toml`
  [5ae59095] + Colors v0.12.10
  [8314cec4] + PGFPlotsX v1.5.2
    Updating `/tmp/jl_SycxIQ/Manifest.toml`
  [dce04be8] + ArgCheck v2.3.0
...
┌ Error: Error during loading of extension
│   exception =
│    1-element ExceptionStack:
│    LoadError: UndefVarError: `Colorant` not defined
│    Stacktrace:
│      [1] getproperty(x::Module, f::Symbol)
│        @ Base ./Base.jl:31
│      [2] top-level scope
│        @ ~/.julia/packages/PGFPlotsX/MBXhp/ext/ColorsExt.jl:7
│      [3] include
│        @ ./Base.jl:451 [inlined]
│      [4] _require(pkg::Base.PkgId, env::Nothing)
│        @ Base ./loading.jl:1657
│      [5] _require_prelocked(uuidkey::Base.PkgId, env::Nothing)
│        @ Base ./loading.jl:1482
│      [6] _require_prelocked(uuidkey::Base.PkgId)
│        @ Base ./loading.jl:1480
│      [7] macro expansion
│        @ ./lock.jl:267 [inlined]
│      [8] require(uuidkey::Base.PkgId)
│        @ Base ./loading.jl:1477

The failure occurs at https://github.com/KristofferC/PGFPlotsX.jl/blob/640377b9c6a9a3f96702e6d34259337aa23828b1/ext/ColorsExt.jl#L7.

It seems we are trying to load the extension too early, before Colors have been fully loaded and has had its symbols populated.

@vtjnash, I might need some help here. If I do e.g. using Colors, then it will start loading its dependencies which triggers checking of extensions. I use Base.loaded_modules to check if a package is loaded but that is apparently not correct since Colors is in that dictionary before it has been properly loaded. Is there a check I can do on a package module to see if it has actually finished loading?