Refactor {{mount}} syntax

packages/ember-glimmer/lib/syntax/mount.js

@@ -13,6 +13,14 @@ import { OutletLayoutCompiler } from './outlet';
 import { FACTORY_FOR } from 'container';
 import AbstractManager from './abstract-manager';
 
+function dynamicEngineFor(vm, symbolTable) {
+  let env     = vm.env;
+  let args    = vm.getArgs();
+  let nameRef = args.positional.at(0);
+
+  return new DynamicEngineReference({ nameRef, env, symbolTable });
+}
+
 /**
   The `{{mount}}` helper lets you embed a routeless engine in a template.
   Mounting an engine will cause an instance to be booted and its `application`
@@ -39,45 +47,75 @@ export function mountMacro(path, params, hash, builder) {
     params.length === 1 && hash === null
   );
 
-  let name = params[0];
-
   assert(
     'The first argument of {{mount}} must be quoted, e.g. {{mount "chat-engine"}}.',
-    typeof name === 'string'
-  );
-
-  assert(
-    `You used \`{{mount '${name}'}}\`, but the engine '${name}' can not be found.`,
-    builder.env.owner.hasRegistration(`engine:${name}`)
+    typeof params[0] === 'string'
   );
 
-  builder.component.static(new MountDefinition(name, builder.env), [params, hash, null, null], builder.symbolTable);
+  let definitionArgs = [params.slice(0, 1), null, null, null];
+  let args = [null, null, null, null];
+  builder.component.dynamic(definitionArgs, dynamicEngineFor, args, builder.symbolTable);
   return true;
 }
 
+class DynamicEngineReference {
+  constructor({ nameRef, env, symbolTable, args }) {
+    this.tag = nameRef.tag;
+    this.nameRef = nameRef;
+    this.env = env;
+    this.symbolTable = symbolTable;
+    this.args = args;
+    this._lastName = undefined;
+    this._lastDef = undefined;
+  }
+
+  value() {
+    let { env, nameRef, /*symbolTable*/ } = this;
+    let nameOrDef = nameRef.value();
+
+    if (this._lastName === nameOrDef) {
+      return this._lastDef;
+    }
+
+    assert(
+      `You used \`{{mount '${nameOrDef}'}}\`, but the engine '${nameOrDef}' can not be found.`,
+      env.owner.hasRegistration(`engine:${nameOrDef}`)
+    );
+
+    if (!env.owner.hasRegistration(`engine:${nameOrDef}`)) {
+      return null;
+    }
+
+    this._lastName = nameOrDef;
+    this._lastDef = new MountDefinition(nameOrDef, env);
+
+    return this._lastDef;
+  }
+}
+
 class MountManager extends AbstractManager {
   prepareArgs(definition, args) {
     return args;
   }
 
-  create(environment, { name, env }, args, dynamicScope) {
-    runInDebug(() => this._pushEngineToDebugStack(`engine:${name}`, env));
+  create(environment, { name }, args, dynamicScope) {
+    runInDebug(() => this._pushEngineToDebugStack(`engine:${name}`, environment));
 
     dynamicScope.outletState = UNDEFINED_REFERENCE;
 
-    let engine = env.owner.buildChildEngineInstance(name);
+    let engine = environment.owner.buildChildEngineInstance(name);
 
     engine.boot();
 
-    return { engine };
+    return engine;
   }
 
-  layoutFor(definition, { engine }, env) {
+  layoutFor(definition, engine, env) {
     let template = engine.lookup(`template:application`);
     return env.getCompiledBlock(OutletLayoutCompiler, template);
   }
 
-  getSelf({ engine }) {
+  getSelf(engine) {
     let applicationFactory = engine[FACTORY_FOR](`controller:application`);
     let factory = applicationFactory || generateControllerFactory(engine, 'application');
     return new RootReference(factory.create());
@@ -87,7 +125,7 @@ class MountManager extends AbstractManager {
     return null;
   }
 
-  getDestructor({ engine }) {
+  getDestructor(engine) {
     return engine;
   }