3 files changed, 122 insertions, 3 deletions
diff --git a/runtime/lua/vim/lsp/semantic_tokens.lua b/runtime/lua/vim/lsp/semantic_tokens.lua
index b1bc48dac6..a9d3d0cbd6 100644
--- a/runtime/lua/vim/lsp/semantic_tokens.lua
+++ b/runtime/lua/vim/lsp/semantic_tokens.lua
@@ -330,7 +330,7 @@ function STHighlighter:process_response(response, client, version)
     end
     vim.list_extend(tokens, old_tokens, idx)
   else
-    tokens = response.data
+    tokens = response.data or {}
   end
 
   -- Update the state with the new results
@@ -378,7 +378,7 @@ function STHighlighter:on_win(topline, botline)
       --
       -- Instead, we have to use normal extmarks that can attach to locations
       -- in the buffer and are persisted between redraws.
-      local highlights = current_result.highlights
+      local highlights = current_result.highlights or {}
       local idx = binary_search(highlights, topline)
 
       for i = idx, #highlights do
@@ -612,7 +612,7 @@ function M.get_at_pos(bufnr, row, col)
 
   local tokens = {}
   for client_id, client in pairs(highlighter.client_state) do
-    local highlights = client.current_result.highlights
+    local highlights = client.current_result.highlights or {}
     if highlights then
       local idx = binary_search(highlights, row)
       for i = idx, #highlights do
diff --git a/runtime/lua/vim/usermark.lua b/runtime/lua/vim/usermark.lua
new file mode 100644
index 0000000000..0d1ec0ae0f
--- /dev/null
+++ b/runtime/lua/vim/usermark.lua
@@ -0,0 +1,68 @@
+-- Defualt implementation of the usermarkfunc. This default implementation is
+-- extensible and allows other plugins to register handlers for different
+-- registers.
+--
+-- The default handler behaves just as a normal register would.
+
+local vim = assert(vim)
+local usermark = {}
+
+-- Returns a "default handler" which behaves like normal global marks. When a
+-- call to set() is made, it stores the current line and col of the cursor and
+-- the filename of the current file.
+function usermark._default_handler()
+  local d = {}
+
+  -- Called when a mark is recalled using the "'" command. Just returns what was
+  -- stored before or nothing if it was never set before.
+  function d.get(self, mark)
+    return self.content or {}
+  end
+
+  -- Called when a mark is set using the "m" command. Stores the current cursor
+  -- position to be recalled at a later time.
+  function d.set(self, mark)
+    local r,c = unpack(vim.api.nvim_win_get_cursor(0))
+    local file = vim.fn.expand("%:p")
+
+    self.content = {
+      line = r;
+      col = c;
+    }
+
+    if file ~= '' then
+      self.content.file = file
+    end
+  end
+
+  return d
+end
+
+-- The store for register default handler
+usermark._marktable = {}
+
+-- Function for the 'usermarkfunc'. Will defer to the handler associated with
+-- the provided mark.
+--
+-- If not handler is registered to a given mark, the default handler is used,
+-- which is a re-implementation of standard mark behavior.
+function usermark.fn(action, mark)
+  if not usermark._marktable[mark] then
+    usermark._marktable[mark] = usermark._default_handler()
+  end
+
+  if action == "get" then
+    return usermark._marktable[mark]:get(mark)
+  else 
+    usermark._marktable[mark]:set(mark)
+    return nil
+  end
+end
+
+-- Registers a handler with a mark. Gets and sets will then defer to this
+-- handler when determining the mark's behavior.
+function usermark.register_handler(mark, handler) 
+  usermark._marktable[mark] = handler
+end
+
+return usermark
diff --git a/runtime/lua/vim/userreg.lua b/runtime/lua/vim/userreg.lua
new file mode 100644
index 0000000000..5abcff0407
--- /dev/null
+++ b/runtime/lua/vim/userreg.lua
@@ -0,0 +1,51 @@
+-- Defualt implementation of the userregfunc. This default implementation is
+-- extensible and allows other plugins to register handlers for different
+-- registers.
+--
+-- The default handler behaves just as a normal register would.
+
+local userreg = {}
+
+-- Returns a "default handler" which behaves exactly like the builtin registers
+-- in Vim. Simply stores whatever was yanked and returns the last thing that was
+-- yanked.
+function userreg._default_handler()
+  local d = {}
+
+  function d.do_yank(self, content)
+    self.content = content
+  end
+
+  function d.do_put(self)
+    return self.content or {}
+  end
+
+  return d
+end
+
+-- The store for registers default handler
+userreg._regtable = {}
+
+-- Function for the userreg. This function will defer to the handler registered
+-- to the given register. If no handler is registered to the given register, the
+-- default handler is used.
+function userreg.fn(action, register, content)
+  if not userreg._regtable[register] then
+    userreg._regtable[register] = userreg._default_handler()
+  end
+
+  if action == "yank" then
+    userreg._regtable[register]:do_yank(content)
+    return nil
+  else 
+    return userreg._regtable[register]:do_put()
+  end
+end
+
+-- Registers a handler with a register. Future yanks and puts will defer to the
+-- handler when determining the content to put/yank.
+function userreg.register_handler(register, handler) 
+  userreg._regtable[register] = handler
+end
+
+return userreg