Improvide diagnostics on lexer exceptions (#12670)

lib/elixir/src/elixir_errors.erl

@@ -8,6 +8,7 @@
 -export([function_error/4, module_error/4, file_error/4]).
 -export([erl_warn/3, file_warn/4]).
 -export([print_diagnostic/1, emit_diagnostic/5]).
+-export([format_snippet/4, format_snippet/5]).
 -export([print_warning/1, print_warning/3]).
 -include("elixir.hrl").
 -type location() :: non_neg_integer() | {non_neg_integer(), non_neg_integer()}.
@@ -27,7 +28,10 @@ print_diagnostic(#{severity := Severity, message := Message, stacktrace := Stack
     case (Stacktrace =:= []) orelse elixir_config:is_bootstrap() of
       true ->
         #{position := Position, file := File} = Diagnostic,
-        file_format(Position, File);
+        case File of 
+          nil -> [];
+          File -> ["\n  ", file_format(Position, File)]
+        end;
 
       false ->
         [["\n  ", 'Elixir.Exception':format_stacktrace_entry(E)] || E <- Stacktrace]
@@ -57,6 +61,82 @@ emit_diagnostic(Severity, Position, File, Message, Stacktrace) ->
 
   ok.
 
+%% Format snippets
+
+format_snippet(File, LineNumber, Column, Description, Snippet) ->
+  #{content := Content, offset := Offset} = Snippet,
+  LineDigits = get_line_number_digits(LineNumber, 1),
+  Spacing = n_spaces(LineDigits + 1),
+  {FormattedSnippet, ColumnsTrimmed} = format_line(Content),
+
+  Formatted = io_lib:format(
+    " ~ts┌─ ~ts~ts\n"
+    " ~ts│\n"
+    " ~p │ ~ts\n"
+    " ~ts│ ~ts\n"
+    " ~ts│\n"
+    " ~ts~ts",
+    [
+     Spacing, prefix(error), file_format({LineNumber, Column}, File),
+     Spacing,
+     LineNumber, FormattedSnippet,
+     Spacing, highlight_below_line(Offset - ColumnsTrimmed, error),
+     Spacing,
+     Spacing, format_message(Description, LineDigits)
+    ]),
+
+  unicode:characters_to_binary(Formatted).
+
+format_snippet(File, LineNumber, Column, Message) ->
+   Formatted = no_line_diagnostic({LineNumber, Column}, File, Message, error),
+   % Left pad so we stay aligned with "** (Exception)" banner
+   Padded = ["   ", string:replace(Formatted, "\n", "\n   ")],
+   unicode:characters_to_binary(Padded).
+
+no_line_diagnostic(Position, File, Message, Severity) -> 
+  io_lib:format(
+    " ┌─ ~ts~ts\n"
+    " ~ts",
+    [
+     prefix(Severity), file_format(Position, File),
+     Message
+    ]
+   ).
+
+format_line(Line) -> 
+  {ok, Re} = re:compile("\s*"),
+  {match, [{_Start, SpacesMatched}]} = re:run(Line, Re, [{capture, all, index}]),
+  case SpacesMatched >= 27 of
+    true ->
+      {Trimmed, _} = trim_line(Line),
+      ColumnsTrimmed = SpacesMatched - 22,
+      {["...", n_spaces(19), Trimmed], ColumnsTrimmed};
+    false ->
+      {Line, 0}
+  end.
+
+trim_line(Line) -> 
+  Trimmed = string:trim(Line, leading),
+  {Trimmed, string:length(Line) - string:length(Trimmed) + 1}.
+
+format_message(Message, NDigits) ->
+  Padding = list_to_binary(["\n  ", n_spaces(NDigits)]),
+  Bin = unicode:characters_to_binary(Message),
+  binary:replace(Bin, <<"\n">>, Padding, [global]).
+
+highlight_below_line(Column, Severity) ->
+  ErrorLength = 1,
+  case Severity of
+    warning ->  highlight([n_spaces(Column), lists:duplicate(ErrorLength, $~)], warning);
+    error -> highlight([n_spaces(Column), lists:duplicate(ErrorLength, $^)], error)
+  end.
+
+get_line_number_digits(Number, Acc) when Number < 10 -> Acc;
+get_line_number_digits(Number, Acc) -> 
+  get_line_number_digits(Number div 10, Acc + 1).
+
+n_spaces(N) -> lists:duplicate(N, " ").
+
 %% Compilation error/warn handling.
 
 %% Low-level warning, should be used only from Erlang passes.
@@ -240,17 +320,19 @@ snippet(InputString, Location, StartLine, StartColumn) ->
 
 %% Helpers
 
-prefix(warning) ->
-  case application:get_env(elixir, ansi_enabled, false) of
-    true -> <<"\e[33mwarning: \e[0m">>;
-    false -> <<"warning: ">>
-  end;
-prefix(error) ->
-  case application:get_env(elixir, ansi_enabled, false) of
-    true -> <<"\e[31merror: \e[0m">>;
-    false -> <<"error: ">>
+prefix(warning) -> highlight(<<"warning: ">>, warning);
+prefix(error) -> highlight(<<"error: ">>, error).
+
+highlight(Message, Severity) ->
+  case {Severity, application:get_env(elixir, ansi_enabled, false)} of
+    {warning, true} -> yellow(Message);
+    {error, true} -> red(Message);
+    _ -> Message
   end.
 
+yellow(Msg) -> io_lib:format("\e[33m~ts\e[0m", [Msg]).
+red(Msg) -> io_lib:format("\e[31m~ts\e[0m", [Msg]).
+
 env_format(Meta, #{file := EnvFile} = E) ->
   {File, Position} = meta_location(Meta, EnvFile),
   Line = ?line(Position),
@@ -273,13 +355,15 @@ env_format(Meta, #{file := EnvFile} = E) ->
 file_format(_, nil) ->
   "";
 file_format({0, _Column}, File) ->
-  ["\n  ", elixir_utils:relative_to_cwd(File)];
+  elixir_utils:relative_to_cwd(File);
+file_format({Line, nil}, File) ->
+  file_format(Line, File);
 file_format({Line, Column}, File) ->
-  io_lib:format("\n  ~ts:~w:~w", [elixir_utils:relative_to_cwd(File), Line, Column]);
+  io_lib:format("~ts:~w:~w", [elixir_utils:relative_to_cwd(File), Line, Column]);
 file_format(0, File) ->
-  ["\n  ", elixir_utils:relative_to_cwd(File)];
+  elixir_utils:relative_to_cwd(File);
 file_format(Line, File) ->
-  io_lib:format("\n  ~ts:~w", [elixir_utils:relative_to_cwd(File), Line]).
+  io_lib:format("~ts:~w", [elixir_utils:relative_to_cwd(File), Line]).
 
 meta_location(Meta, File) ->
   case elixir_utils:meta_keep(Meta) of