Produce clearer messages for syntax errors before a sigil

Closes #3130

Signed-off-by: José Valim <jose.valim@plataformatec.com.br>

Author: oneeman

lib/elixir/src/elixir_errors.erl

@@ -55,6 +55,13 @@ parse_error(Line, File, Error, <<>>) ->
 parse_error(Line, File, <<"syntax error before: ">>, <<"'end'">>) ->
   do_raise(Line, File, 'Elixir.SyntaxError', <<"unexpected token: end">>);
 
+%% Produce a human-readable message for errors before a sigil
+parse_error(Line, File, <<"syntax error before: ">>, <<"{sigil,", _Rest/binary>> = Full) ->
+  {ok, Tokens, _} = erl_scan:string(binary_to_list(Full)),
+  {ok, {sigil, _, Sigil, [Content], _}} = erl_parse:parse_term(Tokens ++ [{dot, 1}]),
+  Message = <<"syntax error before: sigil ~", Sigil," with content '", Content/binary, "'">>,
+  do_raise(Line, File, 'Elixir.SyntaxError', Message);
+
 %% Aliases are wrapped in ['']
 parse_error(Line, File, Error, <<"['", Token/binary>>) when is_binary(Error) ->
   Rest =

lib/elixir/test/elixir/kernel/errors_test.exs

@@ -89,6 +89,12 @@ defmodule Kernel.ErrorsTest do
       '+.foo'
   end
 
+  test :syntax_error_before_sigil do
+    assert_compile_fail SyntaxError,
+      "nofile:1: syntax error before: sigil ~s with content 'bar baz'",
+      '~s(foo) ~s(bar baz)'
+  end
+
   test :compile_error_on_op_ambiguity do
     msg = "nofile:1: \"a -1\" looks like a function call but there is a variable named \"a\", " <>
           "please use explicit parenthesis or even spaces"