Fix yarn version which yields same output as yarn --version (#2491)…

… (#2510)

* Fix `yarn version` which yields same output as `yarn --version` (#2491)

There was a conflict when commander attempts to parse the incoming args
between the command executed and the options since the name `version`
was shared. In other words, executing the command `yarn version`
would yield the same output as `yarn --version`. This relates to PR #2268.

* Shift first arg that shares name with an option to circumvent conflicting name bug

Relating to tj/commander.js#346, when an arg shares the same name as an
option, it wrongly ignores the arg command and executes the option
instead. Therefore, executing 'yarn version' would instead translate
to 'yarn --version'. This logic can subsequently be removed once this issue is resolved.

src/cli/index.js

@@ -38,6 +38,12 @@ for (let i = 0; i < args.length; i++) {
   }
 }
 
+// NOTE: Pending resolution of https://github.com/tj/commander.js/issues/346
+// Remove this (and subsequent use in the logic below) after bug is resolved and issue is closed
+const ARGS_THAT_SHARE_NAMES_WITH_OPTIONS = [
+  'version',
+];
+
 // set global options
 commander.version(pkg.version);
 commander.usage('[command] [flags]');
@@ -172,6 +178,11 @@ if (commandName === 'help' || args.indexOf('--help') >= 0 || args.indexOf('-h')
 
 // parse flags
 args.unshift(commandName);
+
+if (ARGS_THAT_SHARE_NAMES_WITH_OPTIONS.indexOf(commandName) >= 0 && args[0] === commandName) {
+  args.shift();
+}
+
 commander.parse(startArgs.concat(args));
 commander.args = commander.args.concat(endArgs);