navigator.lua/lua/navigator/foldlsp.lua

local log = require"navigator.util".log
local mk_handler = require"navigator.util".mk_handler

local lsp = vim.lsp
local api = vim.api

local M = {}

-- TODO: per-buffer fold table?
M.current_buf_folds = {}

-- Informative table keeping track of language servers that implement textDocument/foldingRange.
-- Not used at runtime (capability is resolved dynamically)
M.servers_supporting_folding = {
  pylsp = true,
  pyright = false,
  sumneko_lua = true,
  texlab = true,
  clangd = false,
  gopls = true,
  julials = false
}

M.active_folding_clients = {}

function M.on_attach()
  M.setup_plugin()
  M.update_folds()
end

function M.setup_plugin()
  api.nvim_command("augroup FoldingCommand")
  api.nvim_command("autocmd! * <buffer>")
  api.nvim_command("autocmd BufEnter <buffer> lua require'navigator.foldlsp'.update_folds()")
  api.nvim_command("autocmd BufWritePost <buffer> lua require'navigator.foldlsp'.update_folds()")
  api.nvim_command("augroup end")

  -- vim.cmd([[
  --
  --   function! folding_nvim#foldexpr()
  --   return luaeval(printf('require"navigator.foldlsp".get_fold_indic(%d)', v:lnum))
  -- endfunction
  --
  --   ]])

  local clients = vim.lsp.buf_get_clients()

  for _, client in pairs(clients) do
    local client_id = client['id']
    if M.active_folding_clients[client_id] == nil then
      local server_supports_folding = client['server_capabilities']['foldingRangeProvider'] or false
      -- if not server_supports_folding then
      --   api.nvim_command(string.format('echom "lsp-folding: %s does not provide folding requests"',
      --                                  client['name']))
      -- end

      M.active_folding_clients[client_id] = server_supports_folding
    end
  end
  -- print(vim.inspect(M.active_folding_clients))
end

function M.update_folds()
  local current_window = api.nvim_get_current_win()
  local in_diff_mode = api.nvim_win_get_option(current_window, 'diff')
  if in_diff_mode then
    -- In diff mode, use diff folding.
    api.nvim_win_set_option(current_window, 'foldmethod', 'diff')
  else
    local clients = lsp.buf_get_clients(0)
    for client_id, client in pairs(clients) do
      if M.active_folding_clients[client_id] then
        -- XXX: better to pass callback in this method or add it directly in the config?
        -- client.config.callbacks['textDocument/foldingRange'] = M.fold_handler
        local current_bufnr = api.nvim_get_current_buf()
        local params = {uri = vim.uri_from_bufnr(current_bufnr)}
        client.request('textDocument/foldingRange', {textDocument = params}, M.fold_handler,
                       current_bufnr)
      end
    end
  end
end

function M.debug_folds()
  for _, table in ipairs(M.current_buf_folds) do
    local start_line = table['startLine']
    local end_line = table['endLine']
    log('startline', start_line, 'endline', end_line)
  end
end

M.fold_handler = mk_handler(function(err, result, ctx, config)
  -- params: err, method, result, client_id, bufnr
  -- XXX: handle err?
  if err or result == nil or #result == 0 then
    print(err, ctx.method, ctx.client_id)
    return
  end
  M.debug_folds()
  local current_bufnr = api.nvim_get_current_buf()
  -- Discard the folding result if buffer focus has changed since the request was
  -- done.
  if current_bufnr == ctx.bufnr then
    for _, fold in ipairs(result) do
      fold['startLine'] = M.adjust_foldstart(fold['startLine'])
      fold['endLine'] = M.adjust_foldend(fold['endLine'])
    end
    table.sort(result, function(a, b)
      return a['startLine'] < b['startLine']
    end)
    M.current_buf_folds = result
    local current_window = api.nvim_get_current_win()
    api.nvim_win_set_option(current_window, 'foldmethod', 'expr')
    api.nvim_win_set_option(current_window, 'foldexpr', 'foldlsp#foldexpr()')
  end
end)

function M.adjust_foldstart(line_no)
  return line_no + 1
end

function M.adjust_foldend(line_no)
  local bufnr = api.nvim_get_current_buf()
  local filetype = api.nvim_buf_get_option(bufnr, 'filetype')
  if filetype == 'lua' then
    return line_no + 2
  else
    return line_no + 1
  end
end

function M.get_fold_indic(lnum)
  local fold_level = 0
  local is_foldstart = false
  local is_foldend = false

  for _, table in ipairs(M.current_buf_folds) do
    local start_line = table['startLine']
    local end_line = table['endLine']

    -- can exit early b/c folds get pre-orderered manually
    if lnum < start_line then
      break
    end

    if lnum >= start_line and lnum <= end_line then
      fold_level = fold_level + 1
      if lnum == start_line then
        is_foldstart = true
      end
      if lnum == end_line then
        is_foldend = true
      end
    end
  end

  if is_foldend and is_foldstart then
    -- If line marks both start and end of folds (like ``else`` statement),
    -- merge the two folds into one by returning the current foldlevel
    -- without any marker.
    return fold_level
  elseif is_foldstart then
    return string.format(">%d", fold_level)
  elseif is_foldend then
    return string.format("<%d", fold_level)
  else
    return fold_level
  end

end

return M