Include `do/end` completion when prefix is `d|`

[zachallaun]

Currently it only appears as a completion when the prefix is specifically a do keyword, but this doesn't work for editors (vscode) that request all their completions after one character.

Originally reported Discord.

[scohen]

I swear we used to have this, it was special cased in completions, and we would check for a trailing d that wasn't part of do and also wasn't the end of another word.

[zachallaun]

We did and still do have do/end completions, but they are only emitted when the prefix is the entire :do operator -- not when the prefix is the single character d. Additionally, it currently overrides all other completions, instead of adding to the list of available completions that largely comes from elixir_sense.

To fix this, we need to modify the current behavior to just include a do/end completion if it's appropriate. The new completion function should look something like:

  defp completions(%Project{} = project, %Env{} = env, %Completion.Context{} = context) do
    prefix_tokens = Env.prefix_tokens(env, 1)

    cond do
      prefix_tokens == [] or not should_emit_completions?(env) ->
        []

      Env.in_context?(env, :struct_field_key) ->
        project
        |> RemoteControl.Api.complete_struct_fields(env.document, env.position)
        |> Enum.map(&Translatable.translate(&1, Builder, env))

      true ->
        {stripped, position} = Builder.strip_struct_operator_for_elixir_sense(env)

        project
        |> RemoteControl.Api.complete(stripped, position)
        |> to_completion_items(project, env, context)

        # HANDLE DO/END SNIPPETS HERE
        |> maybe_add_do_end_snippet(env)
    end
  end

[scohen]

Yeah, I see that code.

[scohen]

@Moosieus should we close this?

[Moosieus]

@scohen Yep, solved with #642!