DeepcopyModules

"You can't really copy what I do because I don't do anything." – David Bailey

A library that provides a function to deepcopy julia Modules, including deep-copying all their contained functions and variables.

(Note that this is essentially a replacement for Base.deepcopy(m::Module), but of course we don't add a method to that function because, arrrr, this package is not a type pirate! ☠️)

Motivation

The goal of this package was to support arbitrary non-intrusive mock-testing, but one can imagine some other uses for this including debugging and interpreting.

See the original proposal here: https://discourse.julialang.org/t/deepcopy-module-and-mocking-for-tests/24214

Usage

deepcopy_module(m::Module)

Returns a newly constructed Module (m2) that is a complete deep-copy of module m, containing deep-copies of all the names in m.

All functions contained in m are deep-copied, so that the returned module m2 contains new generic function objects that have all the same methods as the functions from m, and all code in the new methods will have been modified so that any references to names in m will now be references to names in m2.

julia> module M;  x = 1;  f() = (global x += 1);  end
Main.M

julia> M2 = deepcopy_module(M)
Main.M

julia> M2.f()  # This only modifies the copy of `x` in M2.
2

julia> M2.x, M.x
(2, 1)

julia> nameof(M2)  # Inside M2, it still believes it's module M
:M

Example Usage: Mocking.jl

The file examples/mocking.jl contains an example of using this package to implement a mock-testing framework:

macro mock_test(_module, setup, test)
    quote
        m2 = $DeepcopyModules.deepcopy_module($(esc(_module)))
        @eval m2 eval($(Expr(:quote, setup)))
        @eval m2 eval($(Expr(:quote, test)))
    end
end

Which can then be used as follows:

julia> @mock_test(
           AppMain,
           begin
               using Test
               run_app_was_triggerred = fill(false)
               AppMain.run_app() = run_app_was_triggerred[] = true
           end,
           @testset "run_app" begin
               AppMain.main(["run"])
               @test run_app_was_triggerred[]
           end)
Test Summary: | Pass  Total
run_app       |    1      1
Test.DefaultTestSet("run_app", Any[], 1, false)