Failed to parse warning when a function matches on a field not in the passed map

Precheck

Take a look at the open issues and be sure that your issue is not already covered.
Be sure your versions of Dialyxir and Erlex are up to date.

Environment

Elixir & Erlang/OTP versions (elixir --version): Erlang/OTP 21 [erts-10.3.1] [source] [64-bit] [smp:4:4] [ds:4:4:10] [async-threads:1] [hipe]

Elixir 1.7.4 (compiled with Erlang/OTP 20)

Which version of Dialyxir are you using? (cat mix.lock | grep dialyxir): "dialyxir": {:hex, :dialyxir, "1.1.0", "c5aab0d6e71e5522e77beff7ba9e08f8e02bad90dfbeffae60eaf0cb47e29488", [:mix], [{:erlex, ">= 0.2.6", [hex: :erlex, repo: "hexpm", optional: false]}], "hexpm", "07ea8e49c45f15264ebe6d5b93799d4dd56a44036cf42d0ad9c960bc266c0b9a"},

Current behavior

Describe current behavior. Include errors, stack traces, and any additional information that might be important here. Error requesting that I report this. Source module:

defmodule FieldMismatch do
def main() do
sub(%{my_type: "set"})
end
defp sub(%{type: "set"}), do: :ok
defp sub(_), do: :error
end

Error:


Please file a bug in https://github.com/jeremyjh/dialyxir/issues with this message.

Failed to parse warning: [{:"#", 1}, {:"{", 1}, {:atom_full, 1, '\'type\''}, {:":=", 1}, {:<, 1}, {:<, 1}, {:int, 1, 115}, {:":", 1}, {:int, 1, 8}, {:atom_part, 1, '/'}, {:atom_part, 1, 'i'}, {:atom_part, 1, 'n'}, {:atom_part, 1, 't'}, {:atom_part, 1, 'e'}, {:atom_part, 1, 'g'}, {:atom_part, 1, 'e'}, {:atom_part, 1, 'r'}, {:atom_part, 1, '-'}, {:atom_part, 1, 'u'}, {:atom_part, 1, 'n'}, {:atom_part, 1, 'i'}, {:atom_part, 1, 't'}, {:":", 1}, {:int, 1, 1}, {:",", 1}, {:int, 1, 101}, {:":", 1}, {:int, 1, 8}, {:atom_part, 1, '/'}, {:atom_part, 1, 'i'}, {:atom_part, 1, 'n'}, {:atom_part, 1, 't'}, {:atom_part, 1, 'e'}, {:atom_part, 1, 'g'}, {:atom_part, 1, 'e'}, {:atom_part, 1, 'r'}, {:atom_part, 1, '-'}, {:atom_part, 1, 'u'}, {:atom_part, 1, 'n'}, {:atom_part, 1, 'i'}, {:atom_part, 1, 't'}, {:":", 1}, {:int, 1, 1}, {:",", 1}, {:int, 1, 116}, {:":", 1}, {:int, 1, 8}, {:atom_part, 1, ...}, {:atom_part, ...}, {...}, ...]

Legacy warning: lib/field_mismatch.ex:5: The pattern #{'type':=<<115:8/integer-unit:1,101:8/integer-unit:1,116:8/integer-unit:1>>} can never match the type #{'mytype':=<<:24>>}



Warning, the error looks a little different if you give a name to the map in the header e.g. `%{type: "set"} = _my_map` or `= my_map`.
(Don't blame me for the _my_map instead of deleting the thing, my colleague did that!)

### Expected behavior
* A short description of the expected behavior.
No errors in the tool (because all of my code is perfect so yours should be too! ;-) )

I did some digging. The dialyxir code uses Erlex to pretty_print the string, which ends up calling :parser.parse which returns {:error, {1, :parser, ['syntax error before: ', '\':\'']}}.

My conclusion is that either dialyzer is printing something that it shouldn't (like the actual character values in the parameter string instead of just <<_:24>>, or maybe the :1 after integer-unit), or that :parser.parse needs to learn a new syntax, either of which you are probably going to have push onto the Erlang folks, but I'm going to leave you to do that since I haven't a clue how or where to do that.

If you can get this fixed in Erlang I would bet you would be able to close a bunch of issues, if only you had sample code for them.

jeremyjh / dialyxir