[feat] extregisters

Implements "extended registers"

Extended registers provide access to a separate namespace of registers
backed by custom lua callback functions.

A new special register ("~) is introduced, which prompts the user for
the name of an extregistr to yank or paste from.

This enables file-backed or cloud-synced or other arbitrary register
behavior.

One can now use:

`"~file_extreg<cr>yy`

to yank into the "file_extreg" register.

AI-assisted: Qwen3-Coder

1 files changed, 69 insertions, 0 deletions

diff --git a/runtime/lua/vim/_extregs.lua b/runtime/lua/vim/_extregs.lua
new file mode 100644
index 0000000000..c03e8fda23
--- /dev/null
+++ b/runtime/lua/vim/_extregs.lua
@@ -0,0 +1,69 @@
+-- vim._extregs: Extended Register system API
+-- Internal Lua bindings for the extregister C API
+
+local M = {}
+
+--- Register a new extregister provider
+---@param name string Provider name
+---@param text_yanked_cb? fun(content:table) Callback for yank operations
+---@param text_put_cb? fun():table Callback for put operations
+---@return integer Provider ID on success, 0 on failure
+function M.register(name, text_yanked_cb, text_put_cb)
+  local ty_ref = text_yanked_cb and nlua_push_lref(global_lstate, text_yanked_cb, true) or LUA_NOREF
+  local tp_ref = text_put_cb and nlua_push_lref(global_lstate, text_put_cb, true) or LUA_NOREF
+  return vim._C._extregs.register(name, ty_ref, tp_ref)
+end
+
+--- Unregister an extregister provider
+---@param name string Provider name to unregister
+---@return boolean true on success, false if not found
+function M.unregister(name)
+  return vim._C._extregs.unregister(name)
+end
+
+--- Bind a character to an extregister provider
+---@param alias string Character to bind (e.g., "@")
+---@param provider_name string Name of provider to bind to
+---@return boolean true on success, false on failure
+function M.bind(alias, provider_name)
+  return vim._C._extregs.bind(alias, provider_name)
+end
+
+--- Unbind a character from an extregister provider
+---@param alias string Character to unbind
+---@return boolean true on success, false if not bound
+function M.unbind(alias)
+  return vim._C._extregs.unbind(alias)
+end
+
+--- Check if a character is bound to an extregister
+---@param alias string Character to check
+---@return boolean true if bound, false otherwise
+function M.is_alias(alias)
+  return vim._C._extregs.is_alias(alias)
+end
+
+--- Get provider ID for an alias
+---@param alias string Bound character
+---@return integer Provider ID on success, 0 if not bound
+function M.get_provider_id(alias)
+  return vim._C._extregs.get_provider_id(alias)
+end
+
+--- Get provider by ID
+---@param id integer Provider ID (1-based index)
+---@return any? Provider on success, nil if not found
+function M.get_provider_by_id(id)
+  local prov = vim._C._extregs.get_provider_by_id(id)
+  return prov or nil
+end
+
+--- Get provider by name
+---@param name string Provider name
+---@return any? Provider on success, nil if not found
+function M.get_provider(name)
+  local prov = vim._C._extregs.get_provider(name)
+  return prov or nil
+end
+
+return M