Function complete_fn_param 

pub(crate) fn complete_fn_param(
    acc: &mut Completions,
    ctx: &CompletionContext<'_>,
    pattern_ctx: &PatternContext,
) -> Option<()>

Complete repeated parameters, both name and type. For example, if all functions in a file have a spam: &mut Spam parameter, a completion with spam: &mut Spam insert text/label will be suggested.

Also complete parameters for closure or local functions from the surrounding defined locals.