Inconsistent namespacing when using modules in Main vs other modules

[jrevels]

This might be intentional, I'm not sure (please close if so):

julia> using BaseBenchmarks # BaseBenchmarks loads BenchmarkTools via `using`

julia> BenchmarkTools # BenchmarkTools is available in Main
BenchmarkTools

julia> module A 
           using BaseBenchmarks
           println(BenchmarkTools)
       end
ERROR: UndefVarError: BenchmarkTools not defined

Alternatively, with a fresh REPL:

julia> module A
           using BaseBenchmarks
       end
A

julia> BaseBenchmarks
BaseBenchmarks

I would expect an UnderVarError to be thrown in all cases. I guess the required packages' modules are all getting loaded into Main when the package is loaded, which is why they're all visible?

[yuyichao]

Dup of #17997