attributes_for(:factory, some_association: foo) returns nil for :some_association

I have searched the issue list for something similar, but I have not found the exact same issue.

The problem is that, given these two models:

factory :employee do
  # various attributes
end

factory :job do
  association :employee, strategy: :build
end

attributes_for ignores any explicit employee assignments:

attributes_for(:job, employee: some_other_employee)[:employee] # this is nil!

build and create do not suffer from this problem. Removing the association annotation from the second factory solves the problem, but then I can't have a default association for create.

The following spec fails on current master:

  it "allows specifying association values" do
    sub = attributes_for(:post, user: User.new)
    expect(sub[:user]).not_to eq nil
  end

Note that the following does work:

  it "allows overriding association keys" do
    sub = attributes_for(:post, user_id: 5)
    expect(sub[:user_id]).to eq 5
  end

Start at the attributes_for entry point and reproduce the failing spec described in the issue with an explicit association value such as User.new. Trace how the association declaration affects the returned attributes, then verify that explicit association values are preserved while the existing association default still works for build or create.