Support completeopt=longest

[Julian]

Feature Description

Hey.

I like the behavior of completeopt=longest generally, namely that if I have:

ford
foobar
foobaz

and I type

foo<tab>

I want to see foob with the pum staying open and ready for me to decide if I want foobar or foobaz by again triggering completion.

I haven't been able to get that behavior, though apologies if I've missed this somewhere.

(My config FWIW at the moment is:

local has_words_before = function()
  local _, col = unpack(vim.api.nvim_win_get_cursor(0))
  local line = vim.api.nvim_get_current_line()
  return col ~= 0 and not line:sub(col, col):match '%s'
end

return {
  {
    'saghen/blink.cmp',
    version = 'v0.*',

    lazy = false,

    ---@module 'blink.cmp'
    ---@type blink.cmp.Config
    opts = {
      keymap = {
        ['<C-space>'] = { 'show', 'show_documentation', 'hide_documentation' },
        ['<C-e>'] = { 'hide', 'fallback' },

        ['<C-p>'] = { 'show', 'select_prev', 'fallback' },
        ['<C-n>'] = { 'show', 'select_next', 'fallback' },

        ['<C-b>'] = { 'scroll_documentation_up', 'fallback' },
        ['<C-f>'] = { 'scroll_documentation_down', 'fallback' },

        ['<Tab>'] = {
          function(cmp)
            if not has_words_before() then
              return
            end
            return cmp.select_and_accept()
          end,
          'snippet_forward',
          'fallback'
        },
        ['<S-Tab>'] = { 'snippet_backward', 'fallback' },
      },
      highlight = { use_nvim_cmp_as_default = true },
      trigger = { signature_help = { enabled = true } },
      documentation = { auto_show = true },
      sources = {
        completion = {
          enabled_providers = { "lsp", "path", "snippets", "buffer", "lazydev" },
        },
        providers = {
          lsp = { fallback_for = { "lazydev" } },
          lazydev = { name = "LazyDev", module = "lazydev.integrations.blink" },
        },
      },
    },
  },
}

And thanks for the plugin!