compatibility with ember-cli-htmlbars serialization

ember-cli-htmlbars has its own idiosyncratic serialization protocol that doesn't work like the one in broccoli-babel-transpiler. This patches over that difference, eliminating the "Your build may be slower..." problem when apps are using AST plugins that expose serialization information.

packages/compat/src/htmlbars-unwrapper.ts

@@ -0,0 +1,4 @@
+export function unwrapPlugin(params: { requireFile: string; buildUsing: string; params: any }) {
+  // eslint-disable-next-line @typescript-eslint/no-require-imports
+  return require(params.requireFile)[params.buildUsing](params.params).plugin;
+}

packages/compat/src/v1-app.ts

@@ -558,6 +558,23 @@ export default class V1App {
       // even if the app was using @embroider/macros, we drop it from the config
       // here in favor of our globally-configured one.
       options.plugins.ast = options.plugins.ast.filter((p: any) => !isEmbroiderMacrosPlugin(p));
+
+      // The parallelization protocol in ember-cli-htmlbars doesn't actually
+      // apply to the AST plugins, it applies to wrappers that
+      // ember-cli-htmlbars keeps around the plugins. Those wrappers aren't
+      // availble to us when we look at the template compiler configuration, so
+      // we need to find them directly out of the registry here. And we need to
+      // provide our own unwrapper shim to pull the real plugin out of the
+      // wrapper after deserializing.
+      for (let wrapper of this.app.registry.load('htmlbars-ast-plugin')) {
+        if (wrapper.parallelBabel && wrapper.plugin && !wrapper.plugin.parallelBabel) {
+          wrapper.plugin.parallelBabel = {
+            requireFile: join(__dirname, 'htmlbars-unwrapper.js'),
+            buildUsing: 'unwrapPlugin',
+            params: wrapper.parallelBabel,
+          };
+        }
+      }
     }
     return options.plugins;
   }