*gettext macros fail with string sigils

[whatyouhide]

import MyApp.Gettext
gettext ~s(foo)

fails with ** (ArgumentError) msgid must be a string literal.

[josevalim]

Weird, I thought we macro expanded them?

[whatyouhide]

We do, I'm not sure why this happens. I'll investigate!

[whatyouhide]

@josevalim ok it's because

Macro.expand (quote do: ~s(foo)), __ENV__
#=> {:<<>>, [], ["foo"]}

but we check for is_binary(msgid) after expanding. I can manually check for the {:<<>>, _, [binary]} pattern.

[josevalim]

Yes, we need to check for :<<>> as long as all entries are binaries. I will update sigil_s to return a binary if such is guaranteed.

[whatyouhide]

Closed by 2f183e3! /cc @josevalim