Optional Mix deps being fetched with rebar3 plugins?

Questions & Help Questions
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3

Would an optional field need to be added here: https://github.com/erlang/rebar3/blob/master/src/rebar_app_info.erl#L79
then checked in maybe_fetch here: https://github.com/erlang/rebar3/blob/master/src/rebar_prv_install_deps.erl#L330 ?
Optional would be set to false if the dep is a top-level dep in the current list?

Looks like hex returns the metadata with the Fetch a Release endpoint according to their docs:

...
              "dependencies": {
                "cowboy": {
                  "requirement": "~> 1.0",
                  "optional": true,
                  "app": "cowboy"
                }
              }