Adding Colorscheme to Neovim conditionally?

Question

I'm trying to create a status line and get the color scheme correctly. I have the function

function GetDiagnosticErrorCount()
  local errorCount = #vim.diagnostic.get(0, { severity = vim.diagnostic.severity.ERROR })
  if (errorCount > 0) then
    return '  ' .. errorCount .. ''
  end
  return ''
end

and would like it to have a colorscheme. My current solution today is to add colorscheme before in the definition of the statusline.

%#StatusLineError#%{luaeval('GetDiagnosticErrorCount()')}%

However, this becomes bad because I don't want the space before the error count to get the highlight, and I don't want the space to be there unless it's needed. The ideal solution would be to be able to add the colorscheme directly in the returned string:

function GetDiagnosticErrorCount()
  local errorCount = #vim.diagnostic.get(0, { severity = vim.diagnostic.severity.ERROR })
  if (errorCount > 0) then
    return ' %#StatusLineError#% ' .. errorCount .. '%'
  end
  return ''
end

But this doesn't work.

Answer 1

As D. Ben Knoble suggested, you can wrap it in %{% ... %} and then it will be evaluated as a statusline string!