Markdown support for Vim

I write a lot of Markdown in work, so it’s worth configuring vim to support it well.

" Recognise ```shell as a block with sh syntax.
let g:vim_markdown_fenced_languages = ['shell=sh']
" Don't indent new lines in lists.
let g:vim_markdown_new_list_item_indent = 0
" Disable mappings; I don't use them, and they conflict with diff mappings
" (e.g. " [c, ]c).
let g:vim_markdown_no_default_key_mappings = 1
" Highlight various types of front matter as used by Hugo.
let g:vim_markdown_frontmatter = 1
let g:vim_markdown_toml_frontmatter = 1
let g:vim_markdown_json_frontmatter = 1
" Support strikethrough.
let g:vim_markdown_strikethrough = 1
" Disable the plugin's folding because it randomly folds and unfolds when
" editing; autocmds will use my simple folding instead.
let g:vim_markdown_folding_disabled = 1

" Load here so the settings above
" take effect when the plugin is loaded.

" Recognise bulleted lists starting with ^\*, so that line wrapping doesn't
" destroy bulleted lists.
autocmd FileType markdown setlocal formatoptions+=n
  \ formatlistpat=^\\s*\\([-*]\\\|[0-9]\\.\\)\\s\\+
" Automatically wrap text at textwidth.
autocmd FileType markdown setlocal formatoptions+=t formatoptions-=l
" Interpret blockquotes (lines starting with '>') as comments, so that line
" wrapping doesn't mangle the blockquote markers.
autocmd FileType markdown setlocal comments=n:>
" Turn on spell checking.
autocmd FileType markdown setlocal spell
" Enable simple folding.
autocmd FileType markdown setlocal foldmethod=expr
  \ foldexpr=MarkdownFolding(v:lnum)

" Configure autoformat on write.
Glaive codefmt plugin[mappings]
augroup autoformat_settings
  autocmd FileType markdown AutoFormatBuffer prettier
augroup END

if ! exists('g:MarkdownMinimumHeaderFoldingLevel')
  let g:MarkdownMinimumHeaderFoldingLevel = 2
function! MarkdownFolding(lnum)
  let l:line = getline(a:lnum)
  let l:matches = matchlist(l:line, '^\(#\+\)')
  if len(l:matches) == 0
    return '='
  let l:length = strlen(l:matches[1])
  if l:length <= 1
    return '='
  return '>' . (l:length - (g:MarkdownMinimumHeaderFoldingLevel - 1))