lsp: fix textDocument/completion handling

fix: #11826
Some lanuguage servers return complementary candidates whose prefixes do not match are also returned.
So we exclude completion candidates whose prefix does not match.
ex) Microsoft python-language-server, rust-analyzer

runtime/lua/vim/lsp.lua

@@ -945,12 +945,14 @@ function lsp.omnifunc(findstart, base)
 
   -- Get the start position of the current keyword
   local textMatch = vim.fn.match(line_to_cursor, '\\k*$')
+  local prefix = line_to_cursor:sub(textMatch+1)
+
   local params = util.make_position_params()
 
   local items = {}
   lsp.buf_request(bufnr, 'textDocument/completion', params, function(err, _, result)
     if err or not result then return end
-    local matches = util.text_document_completion_list_to_complete_items(result)
+    local matches = util.text_document_completion_list_to_complete_items(result, prefix)
     -- TODO(ashkan): is this the best way to do this?
     vim.list_extend(items, matches)
     vim.fn.complete(textMatch+1, items)

runtime/lua/vim/lsp/callbacks.lua

@@ -63,8 +63,9 @@ M['textDocument/completion'] = function(_, _, result)
   local line = assert(api.nvim_buf_get_lines(0, row-1, row, false)[1])
   local line_to_cursor = line:sub(col+1)
   local textMatch = vim.fn.match(line_to_cursor, '\\k*$')
+  local prefix = line_to_cursor:sub(textMatch+1)
 
-  local matches = util.text_document_completion_list_to_complete_items(result)
+  local matches = util.text_document_completion_list_to_complete_items(result, prefix)
   vim.fn.complete(textMatch+1, matches)
 end
 

runtime/lua/vim/lsp/util.lua

@@ -129,6 +129,19 @@ function M.extract_completion_items(result)
   end
 end
 
+-- Some lanuguage servers return complementary candidates whose prefixes do not match are also returned.
+-- So we exclude completion candidates whose prefix does not match.
+function M.remove_unmatch_completion_items(items, prefix)
+  local matched_items = {}
+  for _, item in ipairs(items) do
+    local word = item.insertText or item.label
+    if vim.startswith(word, prefix) then
+      table.insert(matched_items, item)
+    end
+  end
+  return matched_items
+end
+
 --- Apply the TextDocumentEdit response.
 -- @params TextDocumentEdit [table] see https://microsoft.github.io/language-server-protocol/specification
 function M.apply_text_document_edit(text_document_edit)
@@ -151,12 +164,14 @@ end
 --- Getting vim complete-items with incomplete flag.
 -- @params CompletionItem[], CompletionList or nil (https://microsoft.github.io/language-server-protocol/specification#textDocument_completion)
 -- @return { matches = complete-items table, incomplete = boolean  }
-function M.text_document_completion_list_to_complete_items(result)
+function M.text_document_completion_list_to_complete_items(result, prefix)
   local items = M.extract_completion_items(result)
   if vim.tbl_isempty(items) then
     return {}
   end
 
+  items = M.remove_unmatch_completion_items(items, prefix)
+
   local matches = {}
 
   for _, completion_item in ipairs(items) do