World age warning for `<Module>.#Unitful_basefactors`

[sostock]

The following warning appears when running the tests in Julia 1.12:

WARNING: Detected access to binding `Main.#Unitful_basefactors` in a world prior to its definition world.
  Julia 1.12 has introduced more strict world age semantics for global bindings.
  !!! This code may malfunction under Revise.
  !!! This code will error in future versions of Julia.
Hint: Add an appropriate `invokelatest` around the access to this binding.
To make this warning an error, and hence obtain a stack trace, use `julia --depwarn=error`.

[giordano]

As the warning message suggests, sprinkling invokelatest should help, but you have to figure out where.

[quachpas]

I am testing on the beta release. I think there is something weird with the unit macro when defining factors of tens before basefactors is defined in the module. The below error does not happen when setting tf to false.

The macro correctly expands to a _basefactors(Main) call, but strangely, manages to get past isdefined(Main, basefactors_name), and that results in an UndefVarError.

My best guess is that this is an upstream bug. It looks like julia is pre-emptively defining the symbol too early such that isdefined returns true when it shouldn't.

UndefVarError stacktrace

❯ julia +beta --depwarn=error --project=@temp
               _
   _       _ _(_)_     |  Documentation: https://docs.julialang.org
  (_)     | (_) (_)    |
   _ _   _| |_  __ _   |  Type "?" for help, "]?" for Pkg help.
  | | | | | | |/ _` |  |
  | | |_| | | | (_| |  |  Version 1.12.0-beta3 (2025-05-12)
 _/ |\__'_|_|_|\__'_|  |  Official https://julialang.org release
|__/                   |

In [1]: using Unitful

In [1]: Unitful.@unit mi "mi" Mile (201168//125)*Unitful.m true
ERROR: LoadError: UndefVarError: `#Unitful_basefactors` not defined in `Main`
Suggestion: define the const at top-level before running function that uses it (stricter Julia v1.12+ rule).
Stacktrace:
 [1] getproperty
   @ ./Base_compiler.jl:47 [inlined]
 [2] _basefactors(m::Module)
   @ Unitful ~/.julia/packages/Unitful/HTQlp/src/Unitful.jl:46
 [3] basefactors_expr(m::Module, n::Expr, basefactor::Expr)
   @ Unitful ~/.julia/packages/Unitful/HTQlp/src/user.jl:305
 [4]
   @ Unitful ~/.julia/packages/Unitful/HTQlp/src/user.jl:346
 [5] top-level scope
   @ ~/.julia/juliaup/julia-1.12.0-beta3+0.x64.linux.gnu/share/julia/stdlib/v1.12/REPL/src/REPL.jl:1848
in expression starting at /home/quachpas/.julia/packages/Unitful/HTQlp/src/user.jl:265
Some type information was truncated. Use `show(err)` to see complete types.

Hence, on the current beta, you get a warning about accessing Main.#Unitful_basefactors before its definition world.

Access to binding before its world age definition

In [1]: using Unitful

In [2]: Unitful.@unit mi "mi" Mile (201168//125)*Unitful.m true
WARNING: Detected access to binding `Main.#Unitful_basefactors` in a world prior to its definition world.
  Julia 1.12 has introduced more strict world age semantics for global bindings.
  !!! This code may malfunction under Revise.
  !!! This code will error in future versions of Julia.
Hint: Add an appropriate `invokelatest` around the access to this binding.
To make this warning an error, and hence obtain a stack trace, use `julia --depwarn=error`.
Out[2]: mi

EDIT: for now, just calling Unitful._basefactors on the module (Main, or others) prior to extensions prevents that issue from happening, e.g.,

Unitful._basefactors(@__MODULE__) # Initialize basefactors
[...] # Units/Dimensions
const localpromotion = copy(Unitful.promotion)
function __init__()
    Unitful.register(YourModule)
    merge!(Unitful.promotion, localpromotion)
end