Vim - add one line above the fold to the folding

Question

When I am coding in vim, I use set foldmethod=syntax which folds my code. It looks something like this then:

How can I add the line above the { to the fold? So that it would look something like this:

So the idea is that it (always) takes the line above the fold into the fold. How can I make this happen?

Answer 1

This needs a custom fold expression (h fold-expr) indenpendently from:

1. foldtext <- you want to fold one more line
2. foldignore <- you still want to fold { and } whatever the indent

In your vimrc:

" Callback: Fold level <- next line indent
function! FoldMethod(lnum)
    let l:indent = max([indent(a:lnum+1), indent(a:lnum)])
    return l:indent / &shiftwidth
endfunction

set foldmethod=expr
set foldexpr=FoldMethod(v:lnum)