Fix incorrect moduledoc for :extras

[unnawut]

Sorry for the consecutive PR. Just found another spot where the example in the @moduledoc is not working. The CONTRIBUTING.md part below is not a valid keyword.

["README.md", "CONTRIBUTING.md": [filename: "contributing", title: "Contributing"]]

This PR changes it to:

["README.md", {"CONTRIBUTING.md", [filename: "contributing", title: "Contributing"]}]

I made sure to finish my work with ex_doc before submitting this PR. So this should be the last one for now.

[wojtekmach]

["a.md": []] is valid syntax, it evaluates to [{:"a.md", []}]. I tested above configuration on local project using ex_doc and it worked as expected - did you run into any issues?

[unnawut]

According to the existing doc, my config would look like this:

extras: [
  "README.md": [filename: "introduction", title: "Introduction"],
  "docs/document.md"
],

And yes it is returning a syntax error:

** (SyntaxError) mix.exs:15: syntax error before: "docs/document.md"
   (elixir) lib/code.ex:334: Code.load_file/2
   (mix) lib/mix/cli.ex:26: Mix.CLI.proceed/1
   (elixir) lib/code.ex:376: Code.require_file/2

Writing this way works fine:

extras: [
  {"README.md", [filename: "introduction", title: "Introduction"]},
  "docs/document.md"
],

Actually... I tried swapping the two extras I have, now this works:

extras: [
  "docs/document.md",
  "README.md": [filename: "introduction", title: "Introduction"]
],

Maybe I'm not familiar with the keyword syntax enough, but the Keyword docs state that "A keyword is a list of two-element tuples where the first element of the tuple is an atom and the second element can be any value". This config allows mainly a list of strings and/or tuples with {"string", []}, so I'm not sure if the keyword syntax can strictly apply here?

But regardless of that, not sure if the sequence of the config values should cause a syntax error here.

[josevalim]

Similar to function calls, you can use the keyword syntax only at the end of the data structure. :) So the example is correct. Thanks for the PR in any case!

[unnawut]

This syntax caveat isn't documented in Keyword. Are you keen to have a PR to the documentation there?

[josevalim]

Good catch. I will change it accordingly! thanks!