Lua Async Await

This is basically ms-jpq/lua-async-await but with Promise like error handling

Refer the original repository for more comprehensive documentation on how all this works

Why?

A Language Server command response contains two parameters. error & response. If the error is present then the error should be handled.

Ex:-

self.client.request('workspace/executeCommand', cmd_info, function(err, res)
  if err then
    log.error(command .. ' failed! arguments: ', arguments, ' error: ', err)
  else
    log.debug(command .. ' success! response: ', res)
  end
end, buffer)

Promises are fine but chaining is annoying specially when you don't have arrow function like syntactic sugar. Moreover, at the time of this is writing, Lua language server generics typing is so primitive and cannot handle Promise<Something> like types.

So I wanted Promise like error handling but without Promises.

How to use

Assume following is the asynchronous API

local function lsp_request(callback)
  local timer = vim.loop.new_timer()

  assert(timer)

  timer:start(2000, 0, function()
    -- First parameter is the error
    callback('something went wrong', nil)
  end)
end

When no error handler defined

This is how you can call this asynchronous API without a callback

local M = require('sync')

M.sync(function()
  local response = M.wait_handle_error(M.wrap(lsp_request)())
end).run()

Result:

Error executing luv callback:
test6.lua:43: unhandled error test6.lua:105: something went wrong
stack traceback:
  [C]: in function 'error'
  test6.lua:43: in function 'callback'
  test6.lua:130: in function <test6.lua:129>

When error handler is defined

local M = require('sync')

local main = M.sync(function()
  local response = M.wait_handle_error(M.wrap(lsp_request)())
end)
  .catch(function(err)
    print('error occurred ', err)
  end)
  .run()

Result:

error occured  test6.lua:105: something went wrong

When nested

local M = require('sync')

local nested = M.sync(function()
  local response = M.wait_handle_error(M.wrap(lsp_request)())
end)

M.sync(function()
  M.wait_handle_error(nested.run)
end)
  .catch(function(err)
    print('parent error handler ' .. err)
  end)
  .run()

Result:

parent error handler test6.lua:105: test6.lua:105: something went wrong