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.

test/functional/lua/system_spec.lua

@@ -0,0 +1,57 @@
+local helpers = require('test.functional.helpers')(after_each)
+local clear = helpers.clear
+local exec_lua = helpers.exec_lua
+local eq = helpers.eq
+
+local function system_sync(cmd, opts)
+  return exec_lua([[
+    return vim.system(...):wait()
+  ]], cmd, opts)
+end
+
+local function system_async(cmd, opts)
+  exec_lua([[
+    local cmd, opts = ...
+    _G.done = false
+    vim.system(cmd, opts, function(obj)
+      _G.done = true
+      _G.ret = obj
+    end)
+  ]], cmd, opts)
+
+  while true do
+    if exec_lua[[return _G.done]] then
+      break
+    end
+  end
+
+  return exec_lua[[return _G.ret]]
+end
+
+describe('vim.system', function()
+  before_each(function()
+    clear()
+  end)
+
+  for name, system in pairs{ sync = system_sync, async = system_async, } do
+    describe('('..name..')', function()
+      it('can run simple commands', function()
+        eq('hello\n', system({'echo', 'hello' }, { text = true }).stdout)
+      end)
+
+      it('handle input', function()
+        eq('hellocat', system({ 'cat' }, { stdin = 'hellocat', text = true }).stdout)
+      end)
+
+      it ('supports timeout', function()
+        eq({
+          code = 0,
+          signal = 2,
+          stdout = '',
+          stderr = "Command timed out: 'sleep 10'"
+        }, system({ 'sleep', '10' }, { timeout = 1 }))
+      end)
+    end)
+  end
+
+end)