Symbol is Base.isexported but not Base.isbindingresolved?

Internals & Design
1

Working on Group import hints by ajwheeler · Pull Request #56753 · JuliaLang/julia · GitHub, I was surprised to see that there are cases of symbols s and modules m for which Base.isbindingresolved(m, s) is false, but Base.isexported(m, s) is true. How does this occur?

2

Welcome! It’s a little funny, but you can export but not define a symbol:

julia> module M
           export foo
       end
Main.M

julia> Base.isbindingresolved(M, :foo)
false

julia> Base.isexported(M, :foo)
true
3

Thanks! Interesting. What is the reason you would do this?

4

It’s typically a bug. It’s not immediately an error because we support writing export statements before the definition — and it’s not uncommon for Packages to do this.

5

Just to add, Aqua.jl can detect this, so it can be used in the tests to prevent merging PRs with undefined exports: Undefined exports · Aqua.jl