Elixir: Cryptic error message when using reserved keyword in pattern match

[JackShannon]

Environment

• Elixir & Erlang/OTP versions (elixir --version): Elixir 1.9.1 (compiled with Erlang/OTP 21)
• Operating system: Ubuntu 18.04

Current behavior

iex(1)> %{after: a} = %{after: 5}
%{after: 5}
iex(2)> %{after: after} = %{after: 5}
** (SyntaxError) iex:2: syntax error before: 'after'

Expected behavior

An error message saying that 'after' is a reserved keyword.

[josevalim]

Good call. We can explicitly check for keywords in syntax error before and add a special note. Thanks for the report!