Precompiled module loading issue

[martinholters]

Given a package

__precompile__()
module Foo
using ProgressMeter
using DataStructures
end

I see

julia> using Foo
┌ Warning: Replacing module `Compat`
└ @ Base loading.jl:350

once Foo has been precompiled (but in a fresh Julia session). I don't think this is specific to PorgressMeter and DataStructures, they just happen to both depend on the same package (Compat) and be loadable on current master. However, it does look like the packages have to be registered.

While this is more or less just an annoyance, I guess the same underlying problem is responsible for something more severe. Consider the package (which unfortunately depends on some patches to FFTW to make it loadable):

__precompile__()
module Foo
using AbstractFFTs
using FFTW
foo() = fft([1])
end

Loading this for the first time, I get

julia> using Foo
[ Info: Recompiling stale cache file /tmp/julia/lib/v0.7/Foo.ji for module Foo

julia> Foo.foo()
# a bunch of deprecation warnings
1-element Array{Complex{Float64},1}:
 1.0 + 0.0im

Repeating (in a fresh session), I get

julia> using Foo
┌ Warning: Replacing module `Compat`
└ @ Base loading.jl:350
┌ Warning: Replacing module `AbstractFFTs`
└ @ Base loading.jl:350

julia> Foo.foo()
WARNING: both AbstractFFTs and FFTW export "fft"; uses of it in module Foo must be qualified
ERROR: UndefVarError: fft not defined
Stacktrace:
 [1] foo() at /tmp/julia/Foo/src/Foo.jl:5
 [2] top-level scope

(Note that FFTW imports AbstractFFTs.fft.)

[martinholters]

Bisection points to f532093, CC @vtjnash

[StefanKarpinski]

I've been seeing this too on #25455 but I thought that it was some change on that branch.