Fix babel plugin cache eviction

Today, babel’s caches (via babel-loader today) expires caches only if the options passed to it change, unfortunately if you upgrade a plugin without changing the configuration options and the file contents remains the same, the cache will not be evicted. This can lead to spurious caching problems if the associated plugins behavior has changed.

To address this defect we now include (when available) the package.json#version of the babel plugins used in our own no-op babel plugin’s configuration. This new no-op plugin is then inserted at the end of the configuration in question.

packages/core/src/app.ts

@@ -38,6 +38,7 @@ import type { Params as InlineBabelParams } from './babel-plugin-inline-hbs-node
 import { PortableHint } from './portable';
 import escapeRegExp from 'escape-string-regexp';
 import { getEmberExports } from './load-ember-template-compiler';
+import resolvePackagePath from 'resolve-package-path';
 
 export type EmberENV = unknown;
 
@@ -144,6 +145,36 @@ export function excludeDotFiles(files: string[]) {
   return files.filter(file => !file.startsWith('.') && !file.includes('/.'));
 }
 
+export const CACHE_BUSTING_PLUGIN = {
+  path: require.resolve('./babel-plugin-cache-busting'),
+  version: readJSONSync('../../package.json').version,
+};
+
+export function addCachablePlugin(babelConfig: TransformOptions) {
+  if (Array.isArray(babelConfig.plugins) && babelConfig.plugins.length > 0) {
+    const plugins = Object.create(null);
+    plugins[CACHE_BUSTING_PLUGIN.path] = CACHE_BUSTING_PLUGIN.version;
+
+    for (const plugin of babelConfig.plugins) {
+      let absolutePathToPlugin: string;
+      if (Array.isArray(plugin) && typeof plugin[0] === 'string') {
+        absolutePathToPlugin = plugin[0] as string;
+      } else if (typeof plugin === 'string') {
+        absolutePathToPlugin = plugin
+      } else {
+        throw new Error(`[Embroider] a babel plugin without an absolute path was from: ${plugin}`)
+      }
+
+      const pkgPath = resolvePackagePath.findUpPackagePath(absolutePathToPlugin);
+      plugins[absolutePathToPlugin] = pkgPath ? readJSONSync(pkgPath).version: undefined;
+    }
+
+    babelConfig.plugins.push([CACHE_BUSTING_PLUGIN.path, {
+      plugins
+    }]);
+  }
+}
+
 class ParsedEmberAsset {
   kind: 'parsed-ember' = 'parsed-ember';
   relativePath: string;
@@ -383,7 +414,9 @@ export class AppBuilder<TreeNames> {
       { absoluteRuntime: __dirname, useESModules: true, regenerator: false },
     ]);
 
-    return makePortable(babel, { basedir: this.root }, this.portableHints);
+    const portable = makePortable(babel, { basedir: this.root }, this.portableHints)
+    addCachablePlugin(portable.config);
+    return portable;
   }
 
   private adjustImportsPlugin(engines: Engine[]): PluginItem {

packages/core/src/babel-plugin-cache-busting.ts

@@ -0,0 +1,4 @@
+
+export default function makePlugin() : any {
+    return { };
+}

packages/core/tests/app.test.ts

@@ -1,4 +1,4 @@
-import { excludeDotFiles } from '../src/app';
+import { excludeDotFiles, addCachablePlugin, CACHE_BUSTING_PLUGIN } from '../src/app';
 
 describe('dot files can be excluded', () => {
   test('excludeDotFiles works', () => {
@@ -10,3 +10,52 @@ describe('dot files can be excluded', () => {
     expect(excludeDotFiles(['foo/bar/baz/.foo.js'])).toEqual([]);
   });
 });
+
+describe('cacheable-plugin', function() {
+  test('noop', function() {
+    const input = {};
+    addCachablePlugin(input)
+    expect(input).toEqual({});
+  });
+
+  test('no plugins', function() {
+    const input = { plugins: []};
+    addCachablePlugin(input)
+    expect(input).toEqual({ plugins: []});
+  });
+
+  test('some plugins', function() {
+    const input = {
+      plugins: [
+        '/nope/not/found',
+        __dirname,
+        [__dirname, []],
+        [`${__dirname}/../`, []],
+        __dirname,
+        [__dirname, []],
+      ]
+    };
+
+    addCachablePlugin(input)
+
+    expect(input).toEqual({
+      plugins: [
+        '/nope/not/found',
+        __dirname,
+        [__dirname, []],
+        [`${__dirname}/../`, []],
+        __dirname,
+        [__dirname, []],
+
+        [CACHE_BUSTING_PLUGIN.path, {
+          plugins: {
+            [CACHE_BUSTING_PLUGIN.path]: CACHE_BUSTING_PLUGIN.version,
+            '/nope/not/found': undefined,
+            [__dirname]: CACHE_BUSTING_PLUGIN.version,
+            [`${__dirname}/../`]: CACHE_BUSTING_PLUGIN.version,
+          }
+        }]
+      ]
+    });
+  });
+});