4 files changed, 57 insertions, 3 deletions
diff --git a/runtime/lua/vim/lsp.lua b/runtime/lua/vim/lsp.lua
index 94f0d62d8d..bc0da25ae5 100644
--- a/runtime/lua/vim/lsp.lua
+++ b/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)
diff --git a/runtime/lua/vim/lsp/callbacks.lua b/runtime/lua/vim/lsp/callbacks.lua
index 794140ee2e..e76e07ca96 100644
--- a/runtime/lua/vim/lsp/callbacks.lua
+++ b/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
 
diff --git a/runtime/lua/vim/lsp/util.lua b/runtime/lua/vim/lsp/util.lua
index 428874f2b7..6b12b37ec2 100644
--- a/runtime/lua/vim/lsp/util.lua
+++ b/runtime/lua/vim/lsp/util.lua
@@ -148,15 +148,36 @@ function M.get_current_line_to_cursor()
   return line:sub(pos[2]+1)
 end
 
+-- Sort by CompletionItem.sortText
+-- https://microsoft.github.io/language-server-protocol/specifications/specification-current/#textDocument_completion
+local function sort_completion_items(items)
+  if items[1] and items[1].sortText then
+    table.sort(items, function(a, b) return a.sortText < b.sortText
+    end)
+  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.
+local function remove_unmatch_completion_items(items, prefix)
+  return vim.tbl_filter(function(item)
+    local word = item.insertText or item.label
+    return vim.startswith(word, prefix)
+  end, items)
+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 = remove_unmatch_completion_items(items, prefix)
+  sort_completion_items(items)
+
   local matches = {}
 
   for _, completion_item in ipairs(items) do
diff --git a/runtime/lua/vim/shared.lua b/runtime/lua/vim/shared.lua
index 6eb7a970e4..498992aa2e 100644
--- a/runtime/lua/vim/shared.lua
+++ b/runtime/lua/vim/shared.lua
@@ -135,6 +135,36 @@ function vim.tbl_values(t)
   return values
 end
 
+--- Apply a function to all values of a table.
+---
+--@param func function or callable table
+--@param t table
+function vim.tbl_map(func, t)
+  vim.validate{func={func,'c'},t={t,'t'}}
+
+  local rettab = {}
+  for k, v in pairs(t) do
+    rettab[k] = func(v)
+  end
+  return rettab
+end
+
+--- Filter a table using a predicate function
+---
+--@param func function or callable table
+--@param t table
+function vim.tbl_filter(func, t)
+  vim.validate{func={func,'c'},t={t,'t'}}
+
+  local rettab = {}
+  for _, entry in pairs(t) do
+    if func(entry) then
+      table.insert(rettab, entry)
+    end
+  end
+  return rettab
+end
+
 --- Checks if a list-like (vector) table contains `value`.
 ---
 --@param t Table to check