fix(rollup): always generate package.json when using @nx/rollup:rollup (#26940)

Prior to Nx 19.4, the `@nx/rollup:rollup` executor generates
`package.json` outside of the actual Rollup build. Nx 19.4 changed this
to be a proper Rollup plugin in order to support inferred targets
better. This led to a slight regression, where projects that override
`plugins` array in their `rollup.config.js` file will also remove the
`generatePackageJson` plugin.

This PR brings the behavior back, so the `package.json` file is _always_
generated regardless of how the `plugins` array is customized.

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## Current Behavior
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## Expected Behavior
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## Related Issue(s)
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Fixes #

e2e/rollup/src/rollup-legacy.test.ts

@@ -198,4 +198,25 @@ describe('Rollup Plugin', () => {
 
     checkFilesExist(`dist/test/index.js`);
   });
+
+  it('should always generate package.json even if the plugin is removed from rollup config file (Nx < 19.4 behavior)', () => {
+    const jsLib = uniq('jslib');
+    runCLI(`generate @nx/js:lib ${jsLib} --bundler rollup --verbose`);
+    updateFile(
+      `libs/${jsLib}/rollup.config.js`,
+      `module.exports = (config) => ({
+        ...config,
+        // Filter out the plugin, but the @nx/rollup:rollup executor should add it back
+        plugins: config.plugins.filter((p) => p.name !== 'rollup-plugin-nx-generate-package-json'),
+      })`
+    );
+    updateJson(join('libs', jsLib, 'project.json'), (config) => {
+      config.targets.build.options.rollupConfig = `libs/${jsLib}/rollup.config.js`;
+      return config;
+    });
+
+    expect(() => runCLI(`build ${jsLib}`)).not.toThrow();
+
+    checkFilesExist(`dist/libs/${jsLib}/package.json`);
+  });
 });

packages/rollup/src/executors/rollup/rollup.impl.ts

@@ -10,6 +10,7 @@ import {
 import { loadConfigFile } from '@nx/devkit/src/utils/config-utils';
 import { createAsyncIterable } from '@nx/devkit/src/utils/async-iterable';
 import { withNx } from '../../plugins/with-nx/with-nx';
+import { pluginName as generatePackageJsonPluginName } from '../../plugins/package-json/generate-package-json';
 import { calculateProjectBuildableDependencies } from '@nx/js/src/utils/buildable-libs-utils';
 
 export async function* rollupExecutor(
@@ -100,6 +101,14 @@ export async function createRollupOptions(
 
   const rollupConfig = withNx(options, {}, dependencies);
 
+  // `generatePackageJson` is a plugin rather than being embedded into @nx/rollup:rollup.
+  // Make sure the plugin is always present to keep the previous before of Nx < 19.4, where it was not a plugin.
+  const generatePackageJsonPlugin = Array.isArray(rollupConfig.plugins)
+    ? rollupConfig.plugins.find(
+        (p) => p['name'] === generatePackageJsonPluginName
+      )
+    : null;
+
   const userDefinedRollupConfigs = options.rollupConfig.map((plugin) =>
     loadConfigFile(plugin)
   );
@@ -122,6 +131,17 @@ export async function createRollupOptions(
       };
     }
   }
+
+  if (
+    generatePackageJsonPlugin &&
+    Array.isArray(finalConfig.plugins) &&
+    !finalConfig.plugins.some(
+      (p) => p['name'] === generatePackageJsonPluginName
+    )
+  ) {
+    finalConfig.plugins.push(generatePackageJsonPlugin);
+  }
+
   return finalConfig;
 }
 

packages/rollup/src/plugins/package-json/generate-package-json.ts

@@ -12,12 +12,14 @@ export interface GeneratePackageJsonOptions {
   additionalEntryPoints?: string[];
 }
 
+export const pluginName = 'rollup-plugin-nx-generate-package-json';
+
 export function generatePackageJson(
   options: GeneratePackageJsonOptions,
   packageJson: PackageJson
 ): Plugin {
   return {
-    name: 'rollup-plugin-nx-generate-package-json',
+    name: pluginName,
     writeBundle: () => {
       updatePackageJson(options, packageJson);
     },