Replace rollup-multi-entry plugin with own plugin

Plugin-multi-entry introduced a breaking change in v7
of always creating a deterministic output which uses sort()
- rollup/plugins#1879

 For the legacy bundle, we need the order of
 dependencies to be fixed.

 Instead of continuing to use this dependency,
 we have our own "plugin" which concatenates
 those files. In the build, we make sure
 that `this` means `window` context and that the
 file as before.

 Async load suggestion by @tombye

Author: kr8n3r

rollup.config.mjs

@@ -1,9 +1,29 @@
 import { nodeResolve } from '@rollup/plugin-node-resolve';
-import multi from '@rollup/plugin-multi-entry';
 import terser from '@rollup/plugin-terser';
 import copy from 'rollup-plugin-copy';
 import styles from "rollup-plugin-styler";
 import postCSSReplace from 'postcss-replace';
+import fs from 'node:fs/promises';
+ 
+
+const LEGACY_BUNDLE_ID = 'legacy-bundle'
+// Simple file concatenation plugin
+const concatenateFiles = (files) => ({
+  // checking ID as it's a virtual module
+  // https://rollupjs.org/plugin-development/#a-simple-example
+  resolveId(id) {
+    if (id === LEGACY_BUNDLE_ID) return id;
+  },
+  async load(id) {
+    if (id === LEGACY_BUNDLE_ID) {
+      const contents = await Promise.all(
+        files.map(file => fs.readFile(file, 'utf-8'))
+      );
+
+      return contents.join('\n');
+    }
+  }
+});
 
 const paths = {
   src: 'app/assets/',
@@ -89,29 +109,27 @@ export default [
   },
   // ES5 JS compilation
   {
-    input: [
-      paths.npm + 'jquery/dist/jquery.min.js',
-      paths.npm + 'timeago/jquery.timeago.js',
-      paths.npm + 'textarea-caret/index.js',
-      paths.npm + 'cbor-js/cbor.js',
-      paths.src + 'javascripts/modules.js',
-      paths.src + 'javascripts/stick-to-window-when-scrolling.js',
-      paths.src + 'javascripts/templateFolderForm.js',
-      paths.src + 'javascripts/main.js',
-    ],
+    input: LEGACY_BUNDLE_ID,
+    context: 'window',
+    external: [],
     output: {
-      dir: paths.dist + 'javascripts/',
-      sourcemap: true
-    },
-    moduleContext: {
-      './node_modules/jquery/dist/jquery.min.js': 'window',
-      './node_modules/cbor-js/cbor.js': 'window',
+      file: paths.dist + 'javascripts/all.js',
+      format: 'cjs',
+      sourcemap: true,
+      exports: 'none',
+      strict: false
     },
     plugins: [
-      nodeResolve(),
-      multi({
-        entryFileName: 'all.js'
-      }),
+      concatenateFiles([
+          paths.npm + 'jquery/dist/jquery.min.js',
+          paths.npm + 'timeago/jquery.timeago.js',
+          paths.npm + 'textarea-caret/index.js',
+          paths.npm + 'cbor-js/cbor.js',
+          paths.src + 'javascripts/modules.js',
+          paths.src + 'javascripts/stick-to-window-when-scrolling.js',
+          paths.src + 'javascripts/templateFolderForm.js',
+          paths.src + 'javascripts/main.js'
+        ]),
       terser({
         ecma: '5'
       }),