Improve error message on oversized atom (#6612)

Author: arcz

lib/elixir/src/elixir_tokenizer.erl

@@ -670,7 +670,7 @@ eol(Line, Column, Tokens) -> [{eol, {Line, Column, Column + 1}} | Tokens].
 unsafe_to_atom(Part, Line, #elixir_tokenizer{}) when
     is_binary(Part) andalso size(Part) > 255;
     is_list(Part) andalso length(Part) > 255 ->
-  {error, {Line, "atom length must be less than system limit", ":"}};
+  {error, {Line, "atom length must be less than system limit: ", [$: | Part]}};
 unsafe_to_atom(Binary, _Line, #elixir_tokenizer{existing_atoms_only=true}) when is_binary(Binary) ->
   {ok, binary_to_existing_atom(Binary, utf8)};
 unsafe_to_atom(Binary, _Line, #elixir_tokenizer{}) when is_binary(Binary) ->

lib/elixir/test/erlang/tokenizer_test.erl

@@ -53,7 +53,7 @@ quoted_atom_test() ->
 
 oversized_atom_test() ->
   OversizedAtom = [$: | string:copies("a", 256)],
-  {1, "atom length must be less than system limit", ":"} = tokenize_error(OversizedAtom).
+  {1, "atom length must be less than system limit: ", OversizedAtom} = tokenize_error(OversizedAtom).
 
 op_atom_test() ->
   [{atom, {1, 1, 6}, f0_1}] = tokenize(":f0_1").