nvim/lua/plugins/null-ls.lua

local null_ls = require("null-ls")

null_ls.setup({
 --[[ on_attach = function(client, bufnr)
    if client.resolved_capabilities.document_formatting then
      vim.cmd("nnoremap <silent><buffer> <Leader>f :lua vim.lsp.buf.formatting()<CR>")
      -- format on save
      vim.cmd("autocmd BufWritePost <buffer> lua vim.lsp.buf.formatting()")
    end
    if client.resolved_capabilities.document_range_formatting then
      vim.cmd("xnoremap <silent><buffer> <Leader>f :lua vim.lsp.buf.range_formatting({})<CR>")
    end 
  end,--]]
  sources = {
    null_ls.builtins.completion.spell,
    null_ls.builtins.diagnostics.codespell,
    null_ls.builtins.diagnostics.markdownlint.with({ extra_args = { "--disable", "MD013", "--" }
  ,}),
    null_ls.builtins.diagnostics.pycodestyle.with({ extra_args = { "--max-line-length=150" }}),
    null_ls.builtins.formatting.black.with({ extra_args = { "--fast" }}),
  },
})