feat: allow parse with no arguments as alias for yargs.argv (#944)

docs/api.md

@@ -20,6 +20,12 @@ or use `.parse()` to do the same thing:
 require('yargs').parse([ '-x', '1', '-y', '2' ])
 ````
 
+Calling `.parse()` with no arguments is equivalent to calling `yargs.argv`:
+
+```javascript
+require('yargs').parse()
+```
+
 The rest of these methods below come in just before the terminating `.argv`.
 
 <a name="alias"></a>.alias(key, alias)
@@ -1007,7 +1013,7 @@ Valid `opt` keys include:
     - `'number'`: synonymous for `number: true`, see [`number()`](#number)
     - `'string'`: synonymous for `string: true`, see [`string()`](#string)
 
-.parse(args, [context], [parseCallback])
+.parse([args], [context], [parseCallback])
 ------------
 
 Parse `args` instead of `process.argv`. Returns the `argv` object.

test/yargs.js

@@ -791,6 +791,17 @@ describe('yargs dsl tests', () => {
       })
       a1.x.should.equal(42)
     })
+
+    it('parses process.argv if no arguments are provided', () => {
+      const r = checkOutput(() => {
+        yargs(['--help'])
+          .command('blerg', 'blerg command')
+          .wrap(null)
+          .parse()
+      })
+
+      r.logs[0].should.match(/Commands:[\s\S]*blerg command/)
+    })
   })
 
   // yargs.parse(['foo', '--bar'], function (err, argv, output) {}

yargs.js

@@ -511,7 +511,8 @@ function Yargs (processArgs, cwd, parentRequire) {
   let parseFn = null
   let parseContext = null
   self.parse = function parse (args, shortCircuit, _parseFn) {
-    argsert('<string|array> [function|boolean|object] [function]', [args, shortCircuit, _parseFn], arguments.length)
+    argsert('[string|array] [function|boolean|object] [function]', [args, shortCircuit, _parseFn], arguments.length)
+    if (typeof args === 'undefined') args = processArgs
 
     // a context object can optionally be provided, this allows
     // additional information to be passed to a command handler.