feat(lsp): show snippet preview if completeopt=popup #32553

Problem:
LSP completion does not show snippet preview.

Solution:
Show snippet preview if 'completeopt' includes popup.

runtime/lua/vim/lsp/completion.lua

@@ -243,6 +243,18 @@ end
 ---@param item lsp.CompletionItem
 ---@return string
 local function get_doc(item)
+  if
+    vim.o.completeopt:find('popup')
+    and item.insertTextFormat == protocol.InsertTextFormat.Snippet
+    and #(item.documentation or '') == 0
+    and vim.bo.filetype ~= ''
+    and (item.textEdit or (item.insertText and item.insertText ~= ''))
+  then
+    -- Shows snippet preview in doc popup if completeopt=popup.
+    local text = parse_snippet(item.insertText or item.textEdit.newText)
+    return ('```%s\n%s\n```'):format(vim.bo.filetype, text)
+  end
+
   local doc = item.documentation
   if not doc then
     return ''

test/functional/plugin/lsp/completion_spec.lua

@@ -750,6 +750,28 @@ describe('vim.lsp.completion: item conversion', function()
     eq(1, #result.items)
     eq('foobar', result.items[1].user_data.nvim.lsp.completion_item.textEdit.newText)
   end)
+
+  it('shows snippet source in doc popup if completeopt include popup', function()
+    exec_lua([[
+      vim.opt.completeopt:append('popup')
+      vim.bo.filetype = 'lua'
+    ]])
+    local completion_list = {
+      isIncomplete = false,
+      items = {
+        {
+          insertText = 'for ${1:index}, ${2:value} in ipairs(${3:t}) do\n\t$0\nend',
+          insertTextFormat = 2,
+          kind = 15,
+          label = 'for .. ipairs',
+          sortText = '0001',
+        },
+      },
+    }
+    local result = complete('|', completion_list)
+    eq('for .. ipairs', result.items[1].word)
+    eq('```lua\nfor index, value in ipairs(t) do\n\t\nend\n```', result.items[1].info)
+  end)
 end)
 
 --- @param name string