Revert breaking group change in order

1fa2971 changed the way groups work when there is only one, leading
to single nested groups being treated as though they were unnested.
Prior to this, if you wanted to group e.g. builtin and external
imports together at the top and everything else together as a second
group, a single nested group was the way to do it

[It appears that this change was unintentional][1], and was made to
try to fix what seems to be a misunderstanding around nested groups
([#2687]). [The docs][2] continue to suggest that nested groups
should be "mingled together" and makes no reference to a single nested
group with no other groups being an invalid option

This therefore reverts the change to how groups work when there is
only one. No documentation change should be necessary given this is
already the described behaviour

[1]: #2687 (comment)
[2]: https://github.com/import-js/eslint-plugin-import/blob/main/docs/rules/order.md#groups-array

CHANGELOG.md

@@ -6,6 +6,9 @@ This change log adheres to standards from [Keep a CHANGELOG](https://keepachange
 
 ## [Unreleased]
 
+### Fixed
+- [`order`]: revert breaking change to single nested group ([#2854], thanks [@yndajas])
+
 ### Changed
 - [Docs] remove duplicate fixable notices in docs ([#2850], thanks [@bmish])
 
@@ -1082,6 +1085,7 @@ for info on changes for earlier releases.
 
 [`memo-parser`]: ./memo-parser/README.md
 
+[#2854]: https://github.com/import-js/eslint-plugin-import/pull/2854
 [#2850]: https://github.com/import-js/eslint-plugin-import/pull/2850
 [#2842]: https://github.com/import-js/eslint-plugin-import/pull/2842
 [#2835]: https://github.com/import-js/eslint-plugin-import/pull/2835
@@ -1887,5 +1891,6 @@ for info on changes for earlier releases.
 [@wtgtybhertgeghgtwtg]: https://github.com/wtgtybhertgeghgtwtg
 [@xM8WVqaG]: https://github.com/xM8WVqaG
 [@xpl]: https://github.com/xpl
+[@yndajas]: https://github.com/yndajas
 [@yordis]: https://github.com/yordis
 [@zloirock]: https://github.com/zloirock

src/rules/order.js

@@ -422,10 +422,6 @@ const types = ['builtin', 'external', 'internal', 'unknown', 'parent', 'sibling'
 // Example: { index: 0, sibling: 1, parent: 1, external: 1, builtin: 2, internal: 2 }
 // Will throw an error if it contains a type that does not exist, or has a duplicate
 function convertGroupsToRanks(groups) {
-  if (groups.length === 1) {
-    // TODO: remove this `if` and fix the bug
-    return convertGroupsToRanks(groups[0]);
-  }
   const rankObject = groups.reduce(function (res, group, index) {
     [].concat(group).forEach(function (groupItem) {
       if (types.indexOf(groupItem) === -1) {

tests/src/rules/order.js

@@ -2753,7 +2753,7 @@ context('TypeScript', function () {
       };
 
       ruleTester.run('order', rule, {
-        valid: [
+        valid: [].concat(
           // #1667: typescript type import support
 
           // Option alphabetize: {order: 'asc'}
@@ -2962,7 +2962,31 @@ context('TypeScript', function () {
               },
             ],
           }),
-        ],
+          isCoreModule('node:child_process') && isCoreModule('node:fs/promises') ? [
+            test({
+              code: `
+                import express from 'express';
+                import log4js from 'log4js';
+                import chpro from 'node:child_process';
+                // import fsp from 'node:fs/promises';
+              `,
+              options: [{
+                groups: [
+                  [
+                    'builtin',
+                    'external',
+                    'internal',
+                    'parent',
+                    'sibling',
+                    'index',
+                    'object',
+                    'type',
+                  ],
+                ],
+              }],
+            }),
+          ] : [],
+        ),
         invalid: [].concat(
           // Option alphabetize: {order: 'asc'}
           test({
@@ -3218,39 +3242,6 @@ context('TypeScript', function () {
                 // { message: '`node:fs/promises` import should occur before import of `express`' },
               ],
             }),
-
-            test({
-              code: `
-                import express from 'express';
-                import log4js from 'log4js';
-                import chpro from 'node:child_process';
-                // import fsp from 'node:fs/promises';
-              `,
-              output: `
-                import chpro from 'node:child_process';
-                import express from 'express';
-                import log4js from 'log4js';
-                // import fsp from 'node:fs/promises';
-              `,
-              options: [{
-                groups: [
-                  [
-                    'builtin',
-                    'external',
-                    'internal',
-                    'parent',
-                    'sibling',
-                    'index',
-                    'object',
-                    'type',
-                  ],
-                ],
-              }],
-              errors: [
-                { message: '`node:child_process` import should occur before import of `express`' },
-                // { message: '`node:fs/promises` import should occur before import of `express`' },
-              ],
-            }),
           ] : [],
         ),
       });