add nvim-ufo for improved folding

lua/custom/plugins/folding.lua

@@ -0,0 +1,61 @@
+-- local foldIcon = ''
+-- local hlgroup = 'NonText'
+-- local function foldTextFormatter(virtText, lnum, endLnum, width, truncate)
+--   local newVirtText = {}
+--   local suffix = '  ' .. foldIcon .. '  ' .. tostring(endLnum - lnum)
+--   local sufWidth = vim.fn.strdisplaywidth(suffix)
+--   local targetWidth = width - sufWidth
+--   local curWidth = 0
+--   for _, chunk in ipairs(virtText) do
+--     local chunkText = chunk[1]
+--     local chunkWidth = vim.fn.strdisplaywidth(chunkText)
+--     if targetWidth > curWidth + chunkWidth then
+--       table.insert(newVirtText, chunk)
+--     else
+--       chunkText = truncate(chunkText, targetWidth - curWidth)
+--       local hlGroup = chunk[2]
+--       table.insert(newVirtText, { chunkText, hlGroup })
+--       chunkWidth = vim.fn.strdisplaywidth(chunkText)
+--       if curWidth + chunkWidth < targetWidth then
+--         suffix = suffix .. (' '):rep(targetWidth - curWidth - chunkWidth)
+--       end
+--       break
+--     end
+--     curWidth = curWidth + chunkWidth
+--   end
+--   table.insert(newVirtText, { suffix, hlgroup })
+--   return newVirtText
+-- end
+
+return {
+  'kevinhwang91/nvim-ufo',
+  dependencies = 'kevinhwang91/promise-async',
+  event = 'BufReadPost',
+  init = function()
+    -- INFO fold commands usually change the foldlevel, which fixes folds, e.g.
+    -- auto-closing them after leaving insert mode, however ufo does not seem to
+    -- have equivalents for zr and zm because there is no saved fold level.
+    -- Consequently, the vim-internal fold levels need to be disabled by setting
+    -- them to 99
+    vim.opt.foldlevel = 99
+    vim.opt.foldlevelstart = 99
+    vim.opt.foldcolumn = 'auto'
+  end,
+  opts = {
+    provider_selector = function(_, ft, _)
+      local lspWithOutFolding = { 'markdown' }
+      if vim.tbl_contains(lspWithOutFolding, ft) then
+        return { 'treesitter', 'indent' }
+      elseif ft == 'html' then
+        return { 'indent' } -- lsp & treesitter do not provide folds
+      else
+        return { 'lsp', 'indent' }
+      end
+    end,
+    -- open opening the buffer, close these fold kinds
+    -- use `:UfoInspect` to get available fold kinds from the LSP
+    close_fold_kinds = { 'imports' },
+    open_fold_hl_timeout = 500,
+    -- fold_virt_text_handler = foldTextFormatter,
+  },
+}