Address misleading warnings from rollup about externals

packages/addon-dev/sample-rollup.config.js

@@ -26,8 +26,14 @@ export default {
     // template colocation.
     babel({
       plugins: ['@embroider/addon-dev/template-colocation-plugin'],
+      babelHelpers: 'bundled',
     }),
 
+    // Follow the V2 Addon rules about dependencies. Your code can import from
+    // `dependencies` and `peerDependencies` as well as standard Ember-provided
+    // package names.
+    addon.dependencies(),
+
     // Ensure that standalone .hbs files are properly integrated as Javascript.
     addon.hbs(),
 

packages/addon-dev/src/rollup-addon-dependencies.ts

@@ -0,0 +1,54 @@
+import type { Plugin } from 'rollup';
+import { readJsonSync } from 'fs-extra';
+import {
+  emberVirtualPackages,
+  emberVirtualPeerDeps,
+  packageName,
+  templateCompilationModules,
+} from '@embroider/shared-internals';
+
+const compilationModules = new Set(
+  templateCompilationModules.map((m) => m.module)
+);
+
+function resolvableDependencies() {
+  let deps = new Set();
+  let pkg = readJsonSync('package.json');
+  if (pkg.dependencies) {
+    for (let name of Object.keys(pkg.dependencies)) {
+      deps.add(name);
+    }
+  }
+  if (pkg.peerDependencies) {
+    for (let name of Object.keys(pkg.peerDependencies)) {
+      deps.add(name);
+    }
+  }
+  return deps;
+}
+
+export default function emberExternals(): Plugin {
+  let deps = resolvableDependencies();
+
+  return {
+    name: 'ember-externals',
+
+    async resolveId(source) {
+      let pkgName = packageName(source);
+      if (!pkgName) {
+        // No package name found means this is a relative import, which we don't
+        // need to deal with.
+        return;
+      }
+
+      if (
+        deps.has(pkgName) ||
+        emberVirtualPeerDeps.has(pkgName) ||
+        emberVirtualPackages.has(pkgName) ||
+        compilationModules.has(pkgName)
+      ) {
+        return { id: source, external: true };
+      }
+    },
+  };
+}

packages/addon-dev/src/rollup.ts

@@ -3,6 +3,7 @@ import { default as publicEntrypoints } from './rollup-public-entrypoints';
 import { default as appReexports } from './rollup-app-reexports';
 import { default as clean } from 'rollup-plugin-delete';
 import { default as keepAssets } from './rollup-keep-assets';
+import { default as dependencies } from './rollup-addon-dependencies';
 import type { Plugin } from 'rollup';
 
 export class Addon {
@@ -63,4 +64,8 @@ export class Addon {
   output() {
     return { dir: this.#destDir, format: 'es', entryFileNames: '[name]' };
   }
+
+  dependencies() {
+    return dependencies();
+  }
 }