`mix do blog.build, compile --force` does not perform compile step

Questions / Help
,
1

I have a custom mix task blog.build that converts markdown files to html files and updates a file current_release in the project root folder with some info about the generated files.

# Mix.Tasks.Blog.Build
def run(_) do
  # ..convert pages, do things..
  # The content of some_info contains a timestamp, so it's different every time
  File.write! "current_release", some_info
  # Mix.Task.reenable "compile" # doesn't change things
end

I also have a Plug.Router that, with some metaprogramming, builds routes from that same current_release file (may not be the best idea but hey):

defmodule MyRouter do
  use Plug.Router

  plug :match
  plug :dispatch
  
  @external_resource release_file = "current_release"

  for {title, file} <- (File.read!(release_file) |> Jason.decode!) do
    # ..define a matcher for every blog post..
  end

  # ..catch all route..
  match(_), do: send_resp(conn, 404, "not found")
end

When I run mix do blog.build, compile on the command line, the compile task is not performed. Same thing when I change the command to mix do blog.build, compile --force.

What also baffles me is that the application is only compiled (before running the tasks) once in every two mix invocations:

$ mix compile                                     # to make sure the application is compiled here
$ mix do blog.build, compile --force              # 1st run
 first-post -> static/1552225911/first-post.html  # output from blog.build
 Current release file updated                     # the @external_resource file (in the router) is updated
                                                  # so that on compile time, the router is marked to be recompiled
                                                  # I expected to see log info from the compiler here,
                                                  # we even forced it to run but it keeps silent.
$ mix do blog.build, compile --force              # 2nd run
 Compiling 2 files (.ex)                          # Before the first task is executed the app is recompiled.
                                                  # That is not unexpected because current_release has changed.
 first-post -> static/1552225914/first-post.html
 Current release file updated
                                                  # Still no compiler action here
$ mix do blog.build, compile --force              # 3rd run
                                                  # NO compilation this time like in the 2nd run?!
 first-post -> static/1552225916/first-post.html
 Current release file updated
                                                  # Still no compiler action here
$ mix do blog.build, compile --force              # 4th run
 Compiling 2 files (.ex)                          # Now its compiling again before running the tasks
 first-post -> static/1552225917/first-post.html
 Current release file updated
                                                  # Still no compiler action here

So my questions are:

  • Why does the compile task never (looks like to) get executed when running mix do blog.build, compile --force?
  • Why does changing the contents of the @external_resource file only triggers a compile every other time?

I’ve already tried to Mix.Task.reenable "compile" in blog.build but that didn’t change things.

Erlang/OTP 21 [erts-10.2.3] [source] [64-bit] [smp:4:4] [ds:4:4:10] [async-threads:1]
Elixir 1.8.1 (compiled with Erlang/OTP 20)
2

Bump. Question summary:

When running mix do mystask, compile --force, the compiler task does not run, while the code has a dependency on an @external_resource that has changed due too mytask.

3

Late to the party, but in case someone lands here later like I did today…

When I run mix do blog.build, compile on the command line, the compile task is not performed.

The reason is that, by design, many Mix tasks are only executed once per invocation, which is the case of compile.

In that case, one solution is to simply call mix twice instead of using mix do, like:

mix blog.build && mix compile

See: