enable deprecated warnings, minimum neovim version 0.9, harden support for greater versions

[alex-courtis]

API changed many times during the 0.10 dev cycle. Many users are using various versions of 0.10 pre-release. We must ensure that the correct functions are being used. Resolves issues such as #2781 (comment)

We can use a lazily loaded cache of supported API. Requires minimum nvim version of 0.9

Testing :h api-level

local log = require "amc.log"

local api_info = vim.fn.api_info()

log.line("version %s", vim.inspect(api_info.version))
log.line("ui_options %s", vim.inspect(api_info.ui_options))

for _, v in ipairs(api_info.functions) do
  if v.deprecated_since and v.deprecated_since ~= 1 then
    log.line("%s %s %s", v.name, vim.inspect(v.since), vim.inspect(v.deprecated_since))
  end
end

0.9.5

version {
  api_compatible = 0,
  api_level = 11,
  api_prerelease = false,
  major = 0,
  minor = 9,
  patch = 5,
  prerelease = false
}

nvim_exec 7 11
nvim_command_output 1 7
nvim_execute_lua 3 7
nvim_buf_get_number 1 2
nvim_buf_clear_highlight 1 7
nvim_buf_set_virtual_text 5 8
nvim_get_hl_by_id 3 9
nvim_get_hl_by_name 3 9

0.10.0

version {
  api_compatible = 0,
  api_level = 12,
  api_prerelease = vim.NIL,
  build = vim.NIL,
  major = 0,
  minor = 10,
  patch = 0,
  prerelease = true
}
nvim_exec 7 11
nvim_command_output 1 7
nvim_execute_lua 3 7
nvim_buf_get_number 1 2
nvim_buf_clear_highlight 1 7
nvim_buf_set_virtual_text 5 8
nvim_get_hl_by_id 3 9
nvim_get_hl_by_name 3 9
nvim_get_option_info 7 11
nvim_set_option 1 11
nvim_get_option 1 11
nvim_buf_get_option 1 11
nvim_buf_set_option 1 11
nvim_win_get_option 1 11
nvim_win_set_option 1 11
nvim_call_atomic 1 12

[gegoune]

We shouldn't be concerned about development versions prior to 0.10. We should support:

• latest release (0.10)
• previous release (0.9)
• current nightly versions (relatively new, 0.11-dev, without many (any?) guarantees)

[alex-courtis]

That works for me. We can continue to use the simple vim.fn test and keep the code clean.

The only issue is users on 0.10 dev versions (debian!), which do break. Could we just show a startup warning like "...proceed at your own risk..." ?

[alex-courtis]

We shouldn't be concerned about development versions prior to 0.10. We should support:

• latest release (0.10)
• previous release (0.9)
• current nightly versions (relatively new, 0.11-dev, without many (any?) guarantees)

I couldn't find a reliable way to detect dev versions; 0.9 is now the minimum and it's up to the user to deal with issues with dev versions.

I did put off that diagnostic breakage until 0.11 as more users will likely raise issues. https://github.com/nvim-tree/nvim-tree.lua/pull/2788/files#diff-b4d683774fedaa8bdc2f7107576331513b01888c09ab2fcfd44468ef976c1b08