Support plug: &fun/1

[wojtekmach]

There was a clause:

plug_fn when is_function(plug_fn) -> {plug_fn, []}

which supported any function but in reality it only allowed 2-arity functions.

This patch adds support for 1-arity functions too. This matches Plug.run/3:

iex> conn = Plug.Test.conn(:get, "/")
iex> plug = fn conn -> Plug.Conn.send_resp(conn, 200, "hi") end
iex> Plug.run(conn, [plug]).resp_body
"hi"

as well as projects along the lines of:

Bypass.stub(bypass, "GET", "/", fn conn -> ... end)

(wink wink)

[mtrudel]

The Plug spec specifically says arity 2 only; is there also a gap in Plug's docs in this respect?

[wojtekmach]

I think that’s a gap yeah, I’ll send docs update and check back here.

[wojtekmach]

I don't think the docs update in that spot would be useful because I believe the vast majority of Plug usage is in the form of:

plug Mod
plug :fun
plug :fun, opts

and these need to be 2-arity.

As mentioned above, &fun/1 is supported by Plug.run so I think this is legit, however mentioning it in that spot would just confuse things IMO.

I understand if you'd rather not pursue this, I'm fine doing fn conn, _ -> or the fn conn, _ -> f.(conn) end trick in my own code.

[wojtekmach]

FWIW I opened elixir-plug/plug#1201.

[mtrudel]

Yep, looks like this all got squared away correctly. Thanks for the effort!