Recursive type definiton throws `UndefVarError` in v1.12 (works on v1.10 and v1.11)

[nickrobinson251]

The following code works in versions 1.10 and v1.11 but throws an error in 1.12.0-DEV.1882

struct ConstantTypeImpl
    value::Any
    function ConstantTypeImpl(c::Any)
        return new(c)
    end
end

struct WrappedTypeImpl
    value::Type
    function WrappedTypeImpl(value::Type)
        new(value)
    end
end

struct _ParamPackedTypeImpl{T}
    value::Vector{T}
end

let
    var"#7#types" = Dict(:_constant => ConstantTypeImpl, :_wrapped => WrappedTypeImpl)

    var"#8#unboxed" = [var"#11#f" for (var"#11#f", var"#9#T") = var"#7#types" if isbitstype(var"#9#T")]

    var"#10#size" = maximum((sizeof(var"#7#types"[var"#11#f"]) for var"#11#f" = var"#8#unboxed"), init=0)

    var"#12#P"() = begin
            Union{Nothing, if :_constant in var"#8#unboxed"
                    Union{}
                else
                    ConstantTypeImpl
                end, if :_wrapped in var"#8#unboxed"
                    Union{}
                else
                    WrappedTypeImpl
                end, if :_packed in var"#8#unboxed"
                    Union{}
                else
                    _ParamPackedTypeImpl{DBType}
                end}
        end

    struct DBType <: Any
        tag::UInt8
        bits::NTuple{var"#10#size", UInt8}
        ptrs::var"#12#P"()
    end
end

julia> include("repro.jl")
ERROR: LoadError: UndefVarError: `DBType` not defined in `Main`
Suggestion: add an appropriate import or assignment. This global was declared but not assigned.
Stacktrace:
 [1] (::var"#10#11"{Vector{Symbol}})()
   @ Main ~/repro.jl:38
 [2] top-level scope
   @ ~/repro.jl:42
 [3] include(mapexpr::Function, mod::Module, _path::String)
   @ Base ./Base.jl:301
 [4] top-level scope
   @ REPL[1]:1
in expression starting at /Users/nickr/repro.jl:19

git bisect points to 435516d / #56497 (cc @Keno)

[Keno]

The change is intentional. The point at which names get published to the global bindings table was ill-defined and it was possible for other users to observe partially-defined data as a result. It also interfered with the 1.12 bindings redesign. To fix this, pass the construction-local reference to the type into the function:

var"#12#P"(DBType=DBType) = ...

and then

ptrs::var"#12#P"(DBType)

(or moral equivalent).

[d-netto]

Applied the fix described above to our codebase.

Code compiles fine now.

CC: @nickrobinson251, @NHDaly.

[nickrobinson251]

Thanks for the explanation, Keno!