add plugin nvim-ufo

Currently there are display issues that needs to be addressed in nvim
core, see https://github.com/kevinhwang91/nvim-ufo/issues/4 .

core/options.vim

@@ -1,7 +1,7 @@
 scriptencoding utf-8
 
 " change fillchars for folding, vertical split, end of buffer, and message separator
-set fillchars=fold:\ ,vert:\│,eob:\ ,msgsep:‾
+set fillchars=fold:\ ,foldopen:,foldsep:\ ,foldclose:,vert:\│,eob:\ ,msgsep:‾
 
 " Paste mode toggle, it seems that Nvim's bracketed paste mode
 " does not work very well for nvim-qt, so we use good-old paste mode

lua/config/lsp.lua

@@ -79,6 +79,11 @@ local capabilities = lsp.protocol.make_client_capabilities()
 capabilities = require('cmp_nvim_lsp').update_capabilities(capabilities)
 capabilities.textDocument.completion.completionItem.snippetSupport = true
 
+capabilities.textDocument.foldingRange = {
+    dynamicRegistration = false,
+    lineFoldingOnly = true
+}
+
 local lspconfig = require("lspconfig")
 
 if utils.executable('pylsp') then

lua/config/nvim-ufo.lua

@@ -0,0 +1,41 @@
+vim.o.foldcolumn = '1'
+vim.o.foldlevel = 99 -- Using ufo provider need a large value, feel free to decrease the value
+vim.o.foldlevelstart = 99
+vim.o.foldenable = true
+
+-- Using ufo provider need remap `zR` and `zM`. If Neovim is 0.6.1, remap yourself
+vim.keymap.set('n', 'zR', require('ufo').openAllFolds)
+vim.keymap.set('n', 'zM', require('ufo').closeAllFolds)
+
+local handler = function(virtText, lnum, endLnum, width, truncate)
+    local newVirtText = {}
+    local suffix = ('  %d '):format(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)
+            -- str width returned from truncate() may less than 2nd argument, need padding
+            if curWidth + chunkWidth < targetWidth then
+                suffix = suffix .. (' '):rep(targetWidth - curWidth - chunkWidth)
+            end
+            break
+        end
+        curWidth = curWidth + chunkWidth
+    end
+    table.insert(newVirtText, {suffix, 'MoreMsg'})
+    return newVirtText
+end
+
+-- global handler
+require('ufo').setup({
+    fold_virt_text_handler = handler
+})

lua/plugins.lua

@@ -357,6 +357,11 @@ packer.startup({
     use { 'ii14/emmylua-nvim', ft = 'lua' }
 
     use { 'j-hui/fidget.nvim', after = 'nvim-lspconfig', config = [[require('config.fidget-nvim')]]}
+
+    -- quick fold
+    use {'kevinhwang91/nvim-ufo', after = 'nvim-lspconfig', config = [[require('config.nvim-ufo')]],
+      requires = 'kevinhwang91/promise-async'
+    }
   end,
   config = {
     max_jobs = 16,