cli: fix duplicate backstage in plugin names

Signed-off-by: Patrik Oldsberg <poldsberg@gmail.com>

.changeset/thick-deers-destroy.md

@@ -0,0 +1,5 @@
+---
+'@backstage/cli': patch
+---
+
+Fix a bug in the translation of the deprecated `--scope` option for the `new` command that could cause plugins to have `backstage-backstage-plugin` in their name.

packages/cli/src/commands/new/new.test.ts

@@ -0,0 +1,45 @@
+/*
+ * Copyright 2025 The Backstage Authors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+import { createNewPackage } from '../../lib/new/createNewPackage';
+import { default as newCommand } from './new';
+
+jest.mock('../../lib/new/createNewPackage');
+
+describe.each([
+  [undefined, undefined, undefined],
+  ['internal', '@internal/', 'backstage-plugin-'],
+  ['internal/', '@internal/', 'backstage-plugin-'],
+  ['acme-backstage', '@acme-backstage/', 'plugin-'],
+  ['acme-backstage/', '@acme-backstage/', 'plugin-'],
+  ['acme-backstage-plugins', '@acme-backstage-plugins/', 'plugin-'],
+])('new', (scope, prefix, infix) => {
+  beforeEach(() => {
+    jest.resetAllMocks();
+  });
+
+  it(`should generate naming options for --scope=${scope}`, async () => {
+    await newCommand({ scope, option: [], skipInstall: false });
+    expect(createNewPackage).toHaveBeenCalledWith(
+      expect.objectContaining({
+        configOverrides: {
+          packageNamePrefix: prefix,
+          packageNamePluginInfix: infix,
+        },
+      }),
+    );
+  });
+});

packages/cli/src/commands/new/new.ts

@@ -42,10 +42,7 @@ export default async (opts: ArgOptions) => {
   let pluginInfix: string | undefined = undefined;
   let packagePrefix: string | undefined = undefined;
   if (scope) {
-    const backstagePrefix = scope.startsWith('backstage') ? '' : 'backstage-';
-    packagePrefix = scope.includes('/')
-      ? `@${scope}${backstagePrefix}`
-      : `@${scope}/${backstagePrefix}`;
+    packagePrefix = scope.includes('/') ? `@${scope}` : `@${scope}/`;
     pluginInfix = scope.includes('backstage') ? 'plugin-' : 'backstage-plugin-';
   }