feat(parser): support short-option groups

README.md

@@ -195,7 +195,8 @@ const { flags, values, positionals } = parseArgs(argv, options);
 - Does the API specify whether a `--` was present/relevant?
   - no
 - Is `-foo` the same as `--foo`?
-  - no, `-foo` is a short option or options (WIP: https://github.com/pkgjs/parseargs/issues/2)
+  - no, `-foo` is a short option or options, with expansion logic that follows the
+    [Utility Syntax Guidelines in POSIX.1-2017](https://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap12.html). `--foo bar`, `withValue: ['foo']`, expands to `-f`, `-o`, `-o bar`.
 - Is `---foo` the same as `--foo`?
   - no 
   - the first flag would be parsed as `'-foo'`

errors.js

@@ -7,16 +7,8 @@ class ERR_INVALID_ARG_TYPE extends TypeError {
   }
 }
 
-class ERR_NOT_IMPLEMENTED extends Error {
-  constructor(feature) {
-    super(`${feature} not implemented`);
-    this.code = 'ERR_NOT_IMPLEMENTED';
-  }
-}
-
 module.exports = {
   codes: {
     ERR_INVALID_ARG_TYPE,
-    ERR_NOT_IMPLEMENTED
   }
 };

index.js

@@ -4,6 +4,7 @@ const {
   ArrayPrototypeConcat,
   ArrayPrototypeIncludes,
   ArrayPrototypeSlice,
+  ArrayPrototypeSplice,
   ArrayPrototypePush,
   ObjectHasOwn,
   StringPrototypeCharAt,
@@ -13,12 +14,6 @@ const {
   StringPrototypeStartsWith,
 } = require('./primordials');
 
-const {
-  codes: {
-    ERR_NOT_IMPLEMENTED
-  }
-} = require('./errors');
-
 const {
   validateArray,
   validateObject
@@ -119,9 +114,14 @@ const parseArgs = (
         );
         return result;
       } else if (StringPrototypeCharAt(arg, 1) !== '-') {
-        // Look for shortcodes: -fXzy
+        // Look for shortcodes: -fXzy and expand them to -f -X -z -y:
         if (arg.length > 2) {
-          throw new ERR_NOT_IMPLEMENTED('short option groups');
+          for (let i = 2; i < arg.length; i++) {
+            const short = StringPrototypeCharAt(arg, i);
+            // Add 'i' to 'pos' such that short options are parsed in order
+            // of definition:
+            ArrayPrototypeSplice(argv, pos + (i - 1), 0, `-${short}`);
+          }
         }
 
         arg = StringPrototypeCharAt(arg, 1); // short

test/index.js

@@ -70,6 +70,58 @@ test('when short option withValue used without value then stored as flag', funct
   t.end();
 });
 
+test('short option group behaves like multiple short options', function(t) {
+  const passedArgs = ['-rf'];
+  const passedOptions = { };
+  const expected = { flags: { r: true, f: true }, values: { r: undefined, f: undefined }, positionals: [] };
+  const args = parseArgs(passedArgs, passedOptions);
+
+  t.deepEqual(args, expected);
+
+  t.end();
+});
+
+test('short option group does not consume subsequent positional', function(t) {
+  const passedArgs = ['-rf', 'foo'];
+  const passedOptions = { };
+  const expected = { flags: { r: true, f: true }, values: { r: undefined, f: undefined }, positionals: ['foo'] };
+  const args = parseArgs(passedArgs, passedOptions);
+  t.deepEqual(args, expected);
+
+  t.end();
+});
+
+// See: Guideline 5 https://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap12.html
+test('if terminal of short-option group configured withValue, subsequent positional is stored', function(t) {
+  const passedArgs = ['-rvf', 'foo'];
+  const passedOptions = { withValue: ['f'] };
+  const expected = { flags: { r: true, f: true, v: true }, values: { r: undefined, v: undefined, f: 'foo' }, positionals: [] };
+  const args = parseArgs(passedArgs, passedOptions);
+  t.deepEqual(args, expected);
+
+  t.end();
+});
+
+test('handles short-option groups in conjunction with long-options', function(t) {
+  const passedArgs = ['-rf', '--foo', 'foo'];
+  const passedOptions = { withValue: ['foo'] };
+  const expected = { flags: { r: true, f: true, foo: true }, values: { r: undefined, f: undefined, foo: 'foo' }, positionals: [] };
+  const args = parseArgs(passedArgs, passedOptions);
+  t.deepEqual(args, expected);
+
+  t.end();
+});
+
+test('handles short-option groups with "short" alias configured', function(t) {
+  const passedArgs = ['-rf'];
+  const passedOptions = { short: { r: 'remove' } };
+  const expected = { flags: { remove: true, f: true }, values: { remove: undefined, f: undefined }, positionals: [] };
+  const args = parseArgs(passedArgs, passedOptions);
+  t.deepEqual(args, expected);
+
+  t.end();
+});
+
 test('Everything after a bare `--` is considered a positional argument', function(t) {
   const passedArgs = ['--', 'barepositionals', 'mopositionals'];
   const expected = { flags: {}, values: {}, positionals: ['barepositionals', 'mopositionals'] };