Xtext LSP Content Assist not showing types with Fragments

Hi,

While using fragments in my grammar, I noticed the types were not showing with the LSP content assist. With the state machine example, I changed the grammar from this:

Transition: event=[Event] '=>' state=[State] ;

to this

fragment StateTransition *: '=>' state=[State] ; Transition: event=[Event] StateTransition ;

And in a unit test that checks the content assist, the "states" are not displayed:

@Test
public void testCompletion()
{
  testCompletion((TestCompletionConfiguration it) -> {
    final var model = "events\n"
              + "    event1 abc\n"
              + "    event2 def\n"
              + "end\n"
              + "\n"
              + "commands\n"
              + "    command1 commandA\n"
              + "    command2 commandB\n"
              + "end\n"
              + "\n"
              + "state initialState\n"
              + "    actions { command1 }\n"
              + "    event1 => nextState\n"
              + "    event2 => finalState\n"
              + "end\n"
              + "\n"
              + "state nextState\n"
              + "    actions { command2 }\n"
              + "    event2 => finalState\n"
              + "end\n"
              + "\n"
              + "state finalState\n"
              + "end\n"
              + "";
      it.setModel(model);
      it.setLine(12);
      it.setColumn(14); // The cursor points after the arrow of "event1" in "initialState"

        final var expected = "finalState (State) -> finalState [[12, 14] .. [12, 14]]\n"
                + "initialState (State) -> initialState [[12, 14] .. [12, 14]]\n"
                + "nextState (State) -> nextState [[12, 14] .. [12, 14]]\n"
                + "";

      it.setExpectedCompletionItems(expected); // actual --> blank
    });
  }

Workaround:

• Customize "IdeContentProposalProvider" and override the _createProposals(CrossReference, ...) method.

• Get the content of the parent method and add the following line if "type" is null: type = context.getCurrentModel().eClass();
  Full method here.

Start by reproducing the unit test's testCompletion case with the grammar fragment and inspect IdeContentProposalProvider, especially createProposals(CrossReference, ...). Compare the completion context and expected items in the example; done means the three State references appear with their State labels and ranges instead of a blank result.