1 files changed, 77 insertions, 0 deletions
diff --git a/runtime/lua/vim/async/_future.lua b/runtime/lua/vim/async/_future.lua
new file mode 100644
index 0000000000..46b036b88c
--- /dev/null
+++ b/runtime/lua/vim/async/_future.lua
@@ -0,0 +1,77 @@
+-- LuaLS cannot model the generic annotations used by this vendored implementation.
+---@diagnostic disable: no-unknown, undefined-doc-name, luadoc-miss-symbol, missing-return, missing-return-value, param-type-mismatch, return-type-mismatch, redundant-return-value, undefined-field, need-check-nil, await-in-sync
+
+local F = vim.F
+local util = require('vim._core.util')
+
+local Future = {}
+Future.__index = Future
+
+function Future:completed()
+  return self._err ~= nil or self._result ~= nil
+end
+
+function Future:result()
+  if not self:completed() then
+    error('Future has not completed', 2)
+  end
+  if self._err ~= nil then
+    return false, self._err
+  else
+    return true, F.unpack_len(self._result)
+  end
+end
+
+function Future:on_complete(callback)
+  if self:completed() then
+    -- Already completed or closed
+    if self._err ~= nil then
+      callback(self._err)
+    else
+      callback(nil, F.unpack_len(self._result))
+    end
+    return function() end
+  end
+
+  local id = self._callback_pos
+  self._callback_pos = id + 1
+  self._callbacks[id] = callback
+
+  return function()
+    self._callbacks[id] = nil
+  end
+end
+
+function Future:complete(err, ...)
+  if self:completed() then
+    error('Future is already completed', 2)
+  end
+
+  if err ~= nil then
+    self._err = err
+  else
+    self._result = F.pack_len(...)
+  end
+
+  local callbacks = self._callbacks
+  self._callbacks = {}
+
+  local errs = {} -- Need to use pairs to avoid gaps caused by removed callbacks
+  for _, cb in pairs(callbacks) do
+    local ok, cb_err = pcall(cb, err, ...)
+    if not ok then
+      errs[#errs + 1] = util._stringify_error(util._normalize_error(cb_err))
+    end
+  end
+
+  if #errs > 0 then
+    error(table.concat(errs, '\n'), 0)
+  end
+end
+
+return function()
+  return setmetatable({
+    _callbacks = {},
+    _callback_pos = 1,
+  }, Future)
+end