defining spec for an array with maps with exactly 1 key fails to validate

Hi, I possibly discovered a bug (or I am missing something). Here the scenario:

Basically there is this message I want to validate using Speck:

{
  "type": "type",
  "data": {
    "devices": [
      {
        "name": "a name"
      }
    ]
  }
}

Then I define the spec according to the docs like this:

struct App.TheSpec

name "the_spec"

attribute :type, :string,    values: ["type"]
attribute :data do

  attribute [:devices] do
    attribute :name,  :string
  end
end

Running my tests results in this error message:

** (ArgumentError) cannot convert the given list to a string.

     To be converted to a string, a list must either be empty or only
     contain the following elements:

       * strings
       * integers representing Unicode code points
       * a list containing one of these three elements

     Please check the given list or call inspect/1 to get the list representation, got:

     [:devices]

Oddly I found out (a workaround) which made it work, by just adding a dummy attribute to the devices array, like this:

struct App.TheSpec

name "the_spec"

attribute :type, :string,    values: ["type"]
attribute :data do

  attribute [:devices] do
    attribute :dummy, :string, optional: true
    attribute :name,  :string
  end
end

So it seems like that Speck has an issue with validating the payload if there are arrays of maps, which only have one key: value pair. As soon as it are at least 2+ key: value pairs, it works.

Is this a legit bug, or am I using it wrong? Thanks for the help.

[amclain]

@robdembitel thanks for the thorough bug report, that was incredibly helpful! This has been fixed and released in v1.0.1.