Themes with highlight groups using "links" to other groups do not propagate colors to SwiftUI properly

I think I figured out why another bug where some themes do not propagate their theme colors to VimR, such as dracula.

I noticed color changes are propagated from
In NvimView+Resize.swift, line 129

autocmd ColorScheme * call rpcnotify(\(channel), 'autocommand', 'colorscheme', get(nvim_get_hl(0, {'id': hlID('Normal')}), 'fg', -1), get(nvim_get_hl(0, {'id': hlID('Normal')}), 'bg', -1), get(nvim_get_hl(0, {'id': hlID('Visual')}), 'fg', -1), get(nvim_get_hl(0, {'id': hlID('Visual')}), 'bg', -1), get(nvim_get_hl(0, {'id': hlID('Directory')}), 'fg', -1), get(nvim_get_hl(0, {'id': hlID('TablineSel')}), 'bg', -1), get(nvim_get_hl(0, {'id': hlID('TablineSel')}), 'fg', -1))

But when I try to get those specific groups in neovim:

echo get(nvim_get_hl(0, {'id': hIID('TablineSel')}, 'fg') 
['bold': vitrue, 'cterm': {'bold': vitrue}, 'link': 'Normal'})

echo get(nvim_get_hl(0, {'id': hIID('TablineFill')}, 'fg') 
({'link': 'DraculaBgDark'})

Because some themes define highlight groups that pull their values from other groups ("link" to other groups), when using the existing code, get(nvim_get_hl(0, {'id': hlID('TablineFill')}), 'bg', -1), the result with these highlight groups is always -1.

Reading up on highlight groups in the neovim docs, they suggest using something more like synIDattr(synIDtrans(hlID('TablineFill')),'bg').

Trying it in my clients, I get:

echo synIDattr(synIDtrans(hlID('TablineFill')),'bg')
#21222c

echo synIDattr(synIDtrans(hlID('TablineFill')),'fg')

This is a lot better, returning with hex color codes starting with #, but it results in empty strings when there is no value set, which could affect how existing code handles missing color codes.

I'm working on a pull-request that changes how the colors are grabbed, without changing how their error handling ( value of -1 ) works; but I wanted to also have this issue to explain the problem.

Start in NvimView+Resize.swift around line 129 and inspect how the ColorScheme autocmd reads the TablineFill and TablineSel highlight groups. Compare linked and directly defined groups in Neovim, then verify that linked colors propagate while missing values retain the existing -1 handling.