fix(lsp): handle non-string documentation in completion items #38291

Problem: `get_doc` throws error with "attempt to get length of a userdata
value" when `item.documentation` is truthy but not a string (e.g. vim.NIL
from a JSON null).

Solution: Check `type(item.documentation)` before taking its length.

runtime/lua/vim/lsp/completion.lua

@@ -261,7 +261,7 @@ local function get_doc(item)
   if
     has_completeopt('popup')
     and item.insertTextFormat == protocol.InsertTextFormat.Snippet
-    and #(item.documentation or '') == 0
+    and (type(item.documentation) ~= 'string' or #item.documentation == 0)
     and vim.bo.filetype ~= ''
     and (item.textEdit or (item.insertText and item.insertText ~= ''))
   then

test/functional/plugin/lsp/completion_spec.lua

@@ -767,11 +767,21 @@ describe('vim.lsp.completion: item conversion', function()
           label = 'for .. ipairs',
           sortText = '0001',
         },
+        {
+          insertText = 'for ${1:i}, ${2:v} in ipairs(${3:t}) do\n\t$0\nend',
+          insertTextFormat = 2,
+          kind = 15,
+          label = 'for .. ipairs 2',
+          sortText = '0002',
+          documentation = vim.NIL,
+        },
       },
     }
     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)
+    eq('for .. ipairs 2', result.items[2].word)
+    eq('```lua\nfor i, v in ipairs(t) do\n\t\nend\n```', result.items[2].info)
   end)
 end)