Add support for -spec attribute completion

apps/els_lsp/src/els_completion_provider.erl

@@ -195,9 +195,9 @@ find_completions(
 find_completions(
     _Prefix,
     ?COMPLETION_TRIGGER_KIND_CHARACTER,
-    #{trigger := <<"-">>, document := Document, column := 1}
+    #{trigger := <<"-">>, document := Document, column := 1, line := Line}
 ) ->
-    attributes(Document);
+    attributes(Document, Line);
 find_completions(
     _Prefix,
     ?COMPLETION_TRIGGER_KIND_CHARACTER,
@@ -304,7 +304,7 @@ find_completions(
             variables(Document);
         %% Check for "-anything"
         [{atom, _, _}, {'-', _}] ->
-            attributes(Document);
+            attributes(Document, Line);
         %% Check for "-export(["
         [{'[', _}, {'(', _}, {atom, _, export}, {'-', _}] ->
             unexported_definitions(Document, function);
@@ -379,6 +379,25 @@ find_completions(
 find_completions(_Prefix, _TriggerKind, _Opts) ->
     [].
 
+-spec try_to_parse_next_function(binary(), line(), line()) ->
+    {ok, els_poi:poi()} | error.
+try_to_parse_next_function(Text, FromL, ToL) when ToL - FromL < 50 ->
+    try els_text:range(Text, {FromL, 1}, {ToL, 1}) of
+        Str ->
+            {ok, POIs} = els_parser:parse(Str),
+            case [P || #{kind := function} = P <- POIs] of
+                [POI | _] ->
+                    {ok, POI};
+                _ ->
+                    try_to_parse_next_function(Text, FromL, ToL + 1)
+            end
+    catch
+        _:_ ->
+            error
+    end;
+try_to_parse_next_function(_, _, _) ->
+    error.
+
 -spec complete_record_field(map(), list()) -> items().
 complete_record_field(_Opts, [{atom, _, _}, {'=', _} | _]) ->
     [];
@@ -458,8 +477,8 @@ complete_type_definition(Document, Name, ItemFormat) ->
 %%=============================================================================
 %% Attributes
 %%=============================================================================
--spec attributes(els_dt_document:item()) -> items().
-attributes(Document) ->
+-spec attributes(els_dt_document:item(), line()) -> items().
+attributes(Document, Line) ->
     [
         snippet(attribute_behaviour),
         snippet(attribute_callback),
@@ -481,7 +500,7 @@ attributes(Document) ->
         snippet(attribute_type),
         snippet(attribute_vsn),
         attribute_module(Document)
-    ] ++ docs_attributes().
+    ] ++ docs_attributes() ++ attribute_spec(Document, Line).
 
 -spec attribute_module(els_dt_document:item()) -> item().
 attribute_module(#{id := Id}) ->
@@ -509,6 +528,26 @@ docs_attributes() ->
     [].
 -endif.
 
+-spec attribute_spec(Document :: els_dt_document:item(), line()) -> items().
+attribute_spec(#{text := Text}, Line) ->
+    case try_to_parse_next_function(Text, Line + 1, Line + 2) of
+        {ok, #{id := {Id, Arity}}} ->
+            Args = [els_arg:new(I, "_") || I <- lists:seq(1, Arity)],
+            SnippetSupport = snippet_support(),
+            FunBin = format_function(Id, Args, SnippetSupport, spec),
+            RetBin =
+                case SnippetSupport of
+                    false ->
+                        <<" -> _.">>;
+                    true ->
+                        N = integer_to_binary(Arity + 1),
+                        <<" -> ${", N/binary, ":_}.">>
+                end,
+            [snippet(<<"-spec">>, <<"spec ", FunBin/binary, RetBin/binary>>)];
+        error ->
+            []
+    end.
+
 %%=============================================================================
 %% Include paths
 %%=============================================================================

apps/els_lsp/test/els_completion_SUITE.erl

@@ -225,6 +225,12 @@ attributes(Config) ->
                 insertTextFormat => ?INSERT_TEXT_FORMAT_SNIPPET,
                 kind => ?COMPLETION_ITEM_KIND_SNIPPET,
                 label => <<"-module(completion_attributes).">>
+            },
+            #{
+                insertText => <<"spec exported_function() -> ${1:_}.">>,
+                insertTextFormat => ?INSERT_TEXT_FORMAT_SNIPPET,
+                kind => ?COMPLETION_ITEM_KIND_SNIPPET,
+                label => <<"-spec">>
             }
         ] ++ docs_attributes(),
     #{result := Completions} =