Typesafe (sorta) templating

For most languages on the beam typing is handled via the positive typing system included with the beam called Dialyzer. Elixir has a fantastic library that makes it so easy to use (it’s not otherwise terribly simple) called Dialyxir.

And yes, it works on templates as well since templates get compiled to normal code.

I just gave it a shot and it did not catch my (contrived) template errors. Is there a configuration that I’m missing?

Hmm, sounds like a bug if so… Let me try a highly simplified test. Given this file:

defmodule EexDialyzeTest do
  @doc """

      iex> EexDialyzeTest.blah()
      Result: 42

  """
  def blah() do
    unquote(EEx.compile_string("Result: <%= 2+thingy() %>"))
  end

  def thingy() do
    :an_atom
  end
end

And the failing test:

  1) doctest EexDialyzeTest.blah/0 (1) (EexDialyzeTestTest)
     test/eex_dialyze_test_test.exs:3
     Doctest failed: got ArithmeticError with message "bad argument in arithmetic expression"
     code: EexDialyzeTest.blah()
     stacktrace:
       (eex_dialyze_test) lib/eex_dialyze_test.ex:1: EexDialyzeTest.blah/0
       (for doctest at) lib/eex_dialyze_test.ex:4: (test)

Then dialyzer ‘should’ catch that, let’s try…

╰─➤  mix dialyzer
Finding suitable PLTs
Checking PLT...
[:compiler, :crypto, :dialyxir, :dialyzer, :elixir, :hipe, :kernel, :logger, :mix, :stdlib, :wx]
PLT is up to date!
Starting Dialyzer
[
  check_plt: false,
  init_plt: '/home/overminddl1/tmp/eex_dialyze_test/_build/dev/dialyxir_erlang-21.0.1_elixir-1.7.0-rc.0_deps-dev.plt',
  files_rec: ['/home/overminddl1/tmp/eex_dialyze_test/_build/dev/lib/eex_dialyze_test/ebin'],
  warnings: [:unknown]
]
Total errors: 2, Skipped: 0
done in 0m2.58s
lib/eex_dialyze_test.ex:1:call
The call:
:erlang.+(2, :an_atom)

will never return since it differs in arguments with
positions 2 from the success typing arguments:

(number(), number())
________________________________________________________________________________
lib/eex_dialyze_test.ex:8:no_return
Function blah/0 has no local return.
________________________________________________________________________________
done (warnings were emitted)

It looks like it caught it just fine? Do you have a reproduceable test case?