fix: temporary fix for libraries that call Object.freeze() (yargs#1483)

test/yargs.js

@@ -2339,4 +2339,20 @@ describe('yargs dsl tests', () => {
         })
     })
   })
+
+  // see: https://github.com/babel/babel/pull/10733
+  it('should not fail if command handler freezes object', () => {
+    const argv = yargs()
+      .command('cmd', 'a command', (yargs) => {
+        yargs.parserConfiguration({ 'populate--': true })
+      }, (argv) => {
+        Object.freeze(argv)
+        argv._.should.eql(['cmd'])
+        argv['--'].should.eql(['foo'])
+      }).parse(['cmd', '--', 'foo'])
+    argv._.should.eql(['cmd', 'foo'])
+    // This should actually not be undefined, once we fix
+    // #1482.
+    argv['--'].should.eql(['foo'])
+  })
 })

yargs.js

@@ -1190,9 +1190,15 @@ function Yargs (processArgs, cwd, parentRequire) {
   // we temporarily populate '--' rather than _, with arguments
   // after the '--' directive. After the parse, we copy these back.
   self._copyDoubleDash = function (argv) {
-    if (!argv._) return argv
+    if (!argv._ || !argv['--']) return argv
     argv._.push.apply(argv._, argv['--'])
-    delete argv['--']
+
+    // TODO(bcoe): refactor command parsing such that this delete is not
+    // necessary: https://github.com/yargs/yargs/issues/1482
+    try {
+      delete argv['--']
+    } catch (_err) {}
+
     return argv
   }