feat(lua): add vim.system()

feat(lua): add vim.system()

Problem:

  Handling system commands in Lua is tedious and error-prone:
  - vim.fn.jobstart() is vimscript and comes with all limitations attached to typval.
  - vim.loop.spawn is too low level

Solution:

  Add vim.system().
  Partly inspired by Python's subprocess module
  Does not expose any libuv objects.

runtime/lua/vim/_system.lua

@@ -0,0 +1,342 @@
+local uv = vim.uv
+
+--- @class SystemOpts
+--- @field cmd string[]
+--- @field stdin string|string[]|true
+--- @field stdout fun(err:string, data: string)|false
+--- @field stderr fun(err:string, data: string)|false
+--- @field cwd? string
+--- @field env? table<string,string|number>
+--- @field clear_env? boolean
+--- @field text boolean?
+--- @field timeout? integer Timeout in ms
+--- @field detach? boolean
+
+--- @class SystemCompleted
+--- @field code integer
+--- @field signal integer
+--- @field stdout? string
+--- @field stderr? string
+
+--- @class SystemState
+--- @field handle uv_process_t
+--- @field timer uv_timer_t
+--- @field pid integer
+--- @field timeout? integer
+--- @field done boolean
+--- @field stdin uv_stream_t?
+--- @field stdout uv_stream_t?
+--- @field stderr uv_stream_t?
+--- @field cmd string[]
+--- @field result? SystemCompleted
+
+---@private
+---@param state SystemState
+local function close_handles(state)
+  for _, handle in pairs({ state.handle, state.stdin, state.stdout, state.stderr }) do
+    if not handle:is_closing() then
+      handle:close()
+    end
+  end
+end
+
+--- @param cmd string[]
+--- @return SystemCompleted
+local function timeout_result(cmd)
+  local cmd_str = table.concat(cmd, ' ')
+  local err = string.format("Command timed out: '%s'", cmd_str)
+  return { code = 0, signal = 2, stdout = '', stderr = err }
+end
+
+--- @class SystemObj
+--- @field pid integer
+--- @field private _state SystemState
+--- @field wait fun(self: SystemObj, timeout?: integer): SystemCompleted
+--- @field kill fun(self: SystemObj, signal: integer)
+--- @field write fun(self: SystemObj, data?: string|string[])
+--- @field is_closing fun(self: SystemObj): boolean?
+local SystemObj = {}
+
+--- @param state SystemState
+--- @return SystemObj
+local function new_systemobj(state)
+  return setmetatable({
+    pid = state.pid,
+    _state = state,
+  }, { __index = SystemObj })
+end
+
+--- @param signal integer
+function SystemObj:kill(signal)
+  local state = self._state
+  state.handle:kill(signal)
+  close_handles(state)
+end
+
+local MAX_TIMEOUT = 2 ^ 31
+
+--- @param timeout? integer
+--- @return SystemCompleted
+function SystemObj:wait(timeout)
+  local state = self._state
+
+  vim.wait(timeout or state.timeout or MAX_TIMEOUT, function()
+    return state.done
+  end)
+
+  if not state.done then
+    self:kill(6) -- 'sigint'
+    state.result = timeout_result(state.cmd)
+  end
+
+  return state.result
+end
+
+--- @param data string[]|string|nil
+function SystemObj:write(data)
+  local stdin = self._state.stdin
+
+  if not stdin then
+    error('stdin has not been opened on this object')
+  end
+
+  if type(data) == 'table' then
+    for _, v in ipairs(data) do
+      stdin:write(v)
+      stdin:write('\n')
+    end
+  elseif type(data) == 'string' then
+    stdin:write(data)
+  elseif data == nil then
+    -- Shutdown the write side of the duplex stream and then close the pipe.
+    -- Note shutdown will wait for all the pending write requests to complete
+    -- TODO(lewis6991): apparently shutdown doesn't behave this way.
+    -- (https://github.com/neovim/neovim/pull/17620#discussion_r820775616)
+    stdin:write('', function()
+      stdin:shutdown(function()
+        if stdin then
+          stdin:close()
+        end
+      end)
+    end)
+  end
+end
+
+--- @return boolean
+function SystemObj:is_closing()
+  local handle = self._state.handle
+  return handle == nil or handle:is_closing()
+end
+
+---@private
+---@param output function|'false'
+---@return uv_stream_t?
+---@return function? Handler
+local function setup_output(output)
+  if output == nil then
+    return assert(uv.new_pipe(false)), nil
+  end
+
+  if type(output) == 'function' then
+    return assert(uv.new_pipe(false)), output
+  end
+
+  assert(output == false)
+  return nil, nil
+end
+
+---@private
+---@param input string|string[]|true|nil
+---@return uv_stream_t?
+---@return string|string[]?
+local function setup_input(input)
+  if not input then
+    return
+  end
+
+  local towrite --- @type string|string[]?
+  if type(input) == 'string' or type(input) == 'table' then
+    towrite = input
+  end
+
+  return assert(uv.new_pipe(false)), towrite
+end
+
+--- @return table<string,string>
+local function base_env()
+  local env = vim.fn.environ()
+  env['NVIM'] = vim.v.servername
+  env['NVIM_LISTEN_ADDRESS'] = nil
+  return env
+end
+
+--- uv.spawn will completely overwrite the environment
+--- when we just want to modify the existing one, so
+--- make sure to prepopulate it with the current env.
+--- @param env? table<string,string|number>
+--- @param clear_env? boolean
+--- @return string[]?
+local function setup_env(env, clear_env)
+  if clear_env then
+    return env
+  end
+
+  --- @type table<string,string|number>
+  env = vim.tbl_extend('force', base_env(), env or {})
+
+  local renv = {} --- @type string[]
+  for k, v in pairs(env) do
+    renv[#renv + 1] = string.format('%s=%s', k, tostring(v))
+  end
+
+  return renv
+end
+
+--- @param stream uv_stream_t
+--- @param text? boolean
+--- @param bucket string[]
+--- @return fun(err: string?, data: string?)
+local function default_handler(stream, text, bucket)
+  return function(err, data)
+    if err then
+      error(err)
+    end
+    if data ~= nil then
+      if text then
+        bucket[#bucket + 1] = data:gsub('\r\n', '\n')
+      else
+        bucket[#bucket + 1] = data
+      end
+    else
+      stream:read_stop()
+      stream:close()
+    end
+  end
+end
+
+local M = {}
+
+--- @param cmd string
+--- @param opts uv.aliases.spawn_options
+--- @param on_exit fun(code: integer, signal: integer)
+--- @param on_error fun()
+--- @return uv_process_t, integer
+local function spawn(cmd, opts, on_exit, on_error)
+  local handle, pid_or_err = uv.spawn(cmd, opts, on_exit)
+  if not handle then
+    on_error()
+    error(pid_or_err)
+  end
+  return handle, pid_or_err --[[@as integer]]
+end
+
+--- Run a system command
+---
+--- @param cmd string[]
+--- @param opts? SystemOpts
+--- @param on_exit? fun(out: SystemCompleted)
+--- @return SystemObj
+function M.run(cmd, opts, on_exit)
+  vim.validate({
+    cmd = { cmd, 'table' },
+    opts = { opts, 'table', true },
+    on_exit = { on_exit, 'function', true },
+  })
+
+  opts = opts or {}
+
+  local stdout, stdout_handler = setup_output(opts.stdout)
+  local stderr, stderr_handler = setup_output(opts.stderr)
+  local stdin, towrite = setup_input(opts.stdin)
+
+  --- @type SystemState
+  local state = {
+    done = false,
+    cmd = cmd,
+    timeout = opts.timeout,
+    stdin = stdin,
+    stdout = stdout,
+    stderr = stderr,
+  }
+
+  -- Define data buckets as tables and concatenate the elements at the end as
+  -- one operation.
+  --- @type string[], string[]
+  local stdout_data, stderr_data
+
+  state.handle, state.pid = spawn(cmd[1], {
+    args = vim.list_slice(cmd, 2),
+    stdio = { stdin, stdout, stderr },
+    cwd = opts.cwd,
+    env = setup_env(opts.env, opts.clear_env),
+    detached = opts.detach,
+    hide = true,
+  }, function(code, signal)
+    close_handles(state)
+    if state.timer then
+      state.timer:stop()
+      state.timer:close()
+    end
+
+    local check = assert(uv.new_check())
+
+    check:start(function()
+      for _, pipe in pairs({ state.stdin, state.stdout, state.stderr }) do
+        if not pipe:is_closing() then
+          return
+        end
+      end
+      check:stop()
+
+      state.done = true
+      state.result = {
+        code = code,
+        signal = signal,
+        stdout = stdout_data and table.concat(stdout_data) or nil,
+        stderr = stderr_data and table.concat(stderr_data) or nil,
+      }
+
+      if on_exit then
+        on_exit(state.result)
+      end
+    end)
+  end, function()
+    close_handles(state)
+  end)
+
+  if stdout then
+    stdout_data = {}
+    stdout:read_start(stdout_handler or default_handler(stdout, opts.text, stdout_data))
+  end
+
+  if stderr then
+    stderr_data = {}
+    stderr:read_start(stderr_handler or default_handler(stderr, opts.text, stderr_data))
+  end
+
+  local obj = new_systemobj(state)
+
+  if towrite then
+    obj:write(towrite)
+    obj:write(nil) -- close the stream
+  end
+
+  if opts.timeout then
+    state.timer = assert(uv.new_timer())
+    state.timer:start(opts.timeout, 0, function()
+      state.timer:stop()
+      state.timer:close()
+      if state.handle and state.handle:is_active() then
+        obj:kill(6) --- 'sigint'
+        state.result = timeout_result(state.cmd)
+        if on_exit then
+          on_exit(state.result)
+        end
+      end
+    end)
+  end
+
+  return obj
+end
+
+return M