1 files changed, 64 insertions, 0 deletions
diff --git a/runtime/lua/vim/userregs.lua b/runtime/lua/vim/userregs.lua
new file mode 100644
index 0000000000..d87dcfefa9
--- /dev/null
+++ b/runtime/lua/vim/userregs.lua
@@ -0,0 +1,64 @@
+local M = {}
+
+-- Table mapping register names (strings) to handler objects
+-- Each handler must implement `yank(regname, contents)` and/or `put(regname)`
+M.handlers = {}
+
+-- Default handler: stores register content in memory
+local default_handler = {
+  registers = {}
+}
+
+--- Called when a register is yanked into (i.e., written)
+---@param regname string
+---@param contents table
+function default_handler.yank(regname, contents)
+  default_handler.registers[regname] = contents
+end
+
+--- Called when a register is put from (i.e., read)
+---@param regname string
+---@return string|table
+function default_handler.put(regname)
+  return default_handler.registers[regname] or ""
+end
+
+--- Register a handler function for one or more register names.
+--- @param register_names string|string[] A register or list of registers
+--- @param handler table A table with `yank()` and/or `put()` methods
+function M.register_handler(register_names, handler)
+  if type(register_names) == "string" then
+    M.handlers[register_names] = handler
+  elseif type(register_names) == "table" then
+    for _, reg in ipairs(register_names) do
+      M.handlers[reg] = handler
+    end
+  else
+    error("register_names must be a string or table of strings")
+  end
+end
+
+--- This is the function Neovim will call via 'userregfunc'.
+--- It dispatches based on the action and register name.
+---@param action string "yank" or "put"
+---@param regname string
+---@param contents any Only passed when action is "yank"
+---@return any Only returned when action is "put"
+function M.fn(action, regname, contents)
+  local handler = M.handlers[regname] or default_handler
+  if action == "yank" and handler.yank then
+    handler.yank(regname, contents)
+  elseif action == "put" and handler.put then
+    return handler.put(regname)
+  else
+    vim.notify(
+      ("[userregs] No valid handler for action %q on register %q"):format(action, regname),
+      vim.log.levels.WARN
+    )
+  end
+end
+
+-- Expose the function to Neovim via 'set userregfunc=v:lua.def_userreg_func'
+_G.def_userreg_func = M.fn
+
+return M