Merge pull request erlang-ls#1178 from gomoripeti/parse_trailing_comment

Fix parsing trailing comments in modules

apps/els_lsp/src/els_parser.erl

@@ -99,12 +99,17 @@ parse_form(Form) ->
 scan_text(Text, StartLoc) ->
  PaddedText = pad_text(Text, StartLoc),
  {ok, Tokens, _Comments, _Cont} = erlfmt_scan:string_node(PaddedText),
- ensure_dot(Tokens).
+ case Tokens of
+ [] -> [];
+ _ -> ensure_dot(Tokens)
+ end.
 
 -spec parse_incomplete_tokens([erlfmt_scan:token()])
  -> {ok, erlfmt_parse:abstract_node()} | error.
 parse_incomplete_tokens([{dot, _}]) ->
  error;
+parse_incomplete_tokens([]) ->
+ error;
 parse_incomplete_tokens(Tokens) ->
  case erlfmt_parse:parse_node(Tokens) of
  {ok, Form} ->
@@ -139,7 +144,7 @@ pad_text(Text, {StartLine, StartColumn}) ->
  ++ lists:duplicate(StartColumn - 1, $\s)
  ++ Text.
 
--spec ensure_dot([erlfmt_scan:token()]) -> [erlfmt_scan:token()].
+-spec ensure_dot([erlfmt_scan:token(), ...]) -> [erlfmt_scan:token(), ...].
 ensure_dot(Tokens) ->
  case lists:last(Tokens) of
  {dot, _} ->

apps/els_lsp/test/els_parser_SUITE.erl

@@ -11,6 +11,7 @@
  , parse_invalid_code/1
  , parse_incomplete_function/1
  , parse_incomplete_spec/1
+ , parse_no_tokens/1
  , underscore_macro/1
  , specs_with_record/1
  , types_with_record/1
@@ -104,6 +105,28 @@ parse_incomplete_spec(_Config) ->
  ?assertMatch([#{id := aa}], parse_find_pois(Text, atom)),
  ok.
 
+%% Issue #1171
+parse_no_tokens(_Config) ->
+ %% scanning text containing only whitespaces returns an empty list of tokens,
+ %% which used to crash els_parser
+ Text1 = " \n ",
+ {ok, []} = els_parser:parse(Text1),
+ %% `els_parser:parse' actually catches the exception and only prints a warning
+ %% log. In order to make sure there is no crash, we need to call an internal
+ %% debug function that would really crash and make the test case fail
+ error = els_parser:parse_incomplete_text(Text1, {1, 1}),
+
+ %% same for text only containing comments
+ Text2 = "%% only a comment",
+ {ok, []} = els_parser:parse(Text2),
+ error = els_parser:parse_incomplete_text(Text2, {1, 1}),
+
+ %% trailing comment, also used to crash els_parser
+ Text3 =
+ "-module(m).\n"
+ "%% trailing comment",
+ {ok, [#{id := m, kind := module}]} = els_parser:parse(Text3).
+
 -spec underscore_macro(config()) -> ok.
 underscore_macro(_Config) ->
  ?assertMatch({ok, [#{id := {'_', 1}, kind := define} | _]},