Hi,

I’m experimenting with macros to create a framework for defining a sort of tests.
I’m trying to figure out how to create a graph of function calls between these macros at compile-time but I’m unsure how to do it.

I have a macro defined as follows.

defmodule MyMacro do
  defmacro test(name, do: body) do
    quote do
      def unquote(name) do
        unquote(name)
      end
    end
  end
end

defmodule MyModule do
  require MyMacro
  import MyMacro

  test first() do
    :first
  end

  test second() do
    x = first()
    y = third()
  end

  test third() do
    :third
  end

What I would like to know, at compile-time, is which test definitions invoke which other test definitions.

So, the result would be that I can inject some module attributes that allow me to determine which test will call which test. In the example above this should be something like: invokes({MyModule, :second}) == [{MyModule, :first}, {MyModule, :third}]`.

Attempt using postwalk

What I have tried so far is using Macro.postwalk to traverse the AST in defmacro test, but in that context you only have access to the __CALLER__ env, and the AST of that particular test definition. With this information I can only determine which functions from other modules are imported and called, and which qualified functions are called. The issue I have here is that I don’t know when an unqualified invocation is actually another function in the module, or something else.

For example, the AST of the second() definition above looks as follows.

{:__block__, [],
 [
   {:=, [line: 10, column: 7],
    [{:x, [line: 10, column: 5], nil}, {:first, [line: 10, column: 9], []}]},
   {:=, [line: 11, column: 7],
    [{:y, [line: 11, column: 5], nil}, {:third, [line: 11, column: 9], []}]}
 ]}

__CALLER__ during macro expansion does not contain the other definitions in the module, so I cannot determine whether they are defined in this module or not.

Ideas

Another idea I had was to use the __after_compile__ callback to then do manual analysis on the module. In the __after_compile__ body you have access the an env that contains which module this invocation is about. Since the module is already compiled, I also have access to __info__(:functions) for that module.

Using this information, I can do a Macro.postwalk on the entire module definition and determine the calls inside each test.

The limitation here is that it’s no longer possible to inject code/module attributes in the module itself. So I don’t really know where to put the result of the analysis at this point.

defmodule MyMacro do
  defmacro __using__(_options) do
    quote do
      import unquote(__MODULE__)

      # module attribute that holds all the examples
      Module.register_attribute(__MODULE__, :test, accumulate: true)

      @after_compile unquote(__MODULE__)
    end
  end

  def __after_compile__(env, _bytecode) do
    module =
      env.module.__info__(:functions)
      |> IO.inspect(label: "functions in #{inspect(env.module)}")

    # analyze the compiled module to build a dependency graph
    analyze_module_here_using_the_env(env.module)

    IO.inspect(env)
  end

  defmacro test(name, do: body) do
    quote do
      # @test {unquote(name), unquote(body)}
      def unquote(name) do
        unquote(name)
      end
    end
  end
end

So in brief, how could I solve this in an elegant way? I’d like to not do these calculations at runtime, but have the information ready at compile-time.