[NullVoxPopuli-ai-agent]

Spike: every classic feature behind EMBER_DROP_CLASSIC_FEATURES in one branch. Do not merge this PR. It shows the end state of the stack and what is still left.

This branch merges all the PRs of the stack onto main. It adds the last group of exports, and puts the core classes on a plain base:

PR	Behind the flag
#21726	the flag
#21740	the 15 computed macros of deprecate-computed-macros
#21744	computed, dependentKeyCompat and the other computed exports
#21741	Evented, Observable, PromiseProxyMixin, ControllerMixin
#21737	Service as a plain class
#21738	Helper as a plain class
#21739	Route on a plain base class
#21742	Controller as a plain class
#21743	EmberObject and CoreObject
this PR	the rest of the exports, and the core classes, in the sections below

New in this PR

With the flag, these exports are undefined:

• Component from @ember/component
• Mixin from @ember/object/mixin
• EmberArray, A, MutableArray, NativeArray from @ember/array, and @ember/array/mutable
• ArrayProxy, ObjectProxy, Enumerable, MutableEnumerable
• observer from @ember/object, and addObserver and removeObserver from @ember/object/observers

Each implementation moves to a private module in the rollup ignore list, as in #21743. Framework code and test files import the private module, so the same tests run in every build.

New tests:

• packages/ember/tests/drop_classic_features_exports_test.js checks that the exports are undefined. It runs only with the flag.
• packages/ember/tests/without-EMBER_DROP_CLASSIC_FEATURES/classic_exports_test.js checks that each public export is the private implementation. It runs only without the flag.

Core classes

With the flag, the exports below are plain classes that extend no other class. The classic classes do not change.

Class	With the flag
Application, ApplicationInstance, Engine, EngineInstance	separate plain classes, which keep the public destroy()
HashLocation, HistoryLocation, NoneLocation	separate plain classes, with setup in the constructor
EmberRouter, EventDispatcher, DataAdapter, ContainerDebugAdapter	a small plain base, because these already set themselves up in the constructor
Namespace	undefined

• Engine builds its registry on first use, so it sees the Resolver field of subclasses.
• Application.create(options) assigns the options, then starts the application. The constructor cannot start it, because the fields of subclasses do not exist yet when it runs.
• The container calls willDestroy, then destroys the router, the locations and the event dispatcher with @ember/destroyable, as for Service.

Tests:

• Engine and application tests register their factories in an initializer, not in init(), so they work on both classes.
• The unit tests of the classic location classes run only without the flag. packages/@ember/routing/tests/location/drop_classic_features_test.js tests the plain ones.
• packages/ember/tests/drop_classic_features_core_classes_test.js checks that no core class extends CoreObject, and checks Application.create, the engine registry and willDestroy.

Rendering without proxies

With the flag:

• get and template property reads do not call unknownProperty.
• set does not call setUnknownProperty.
• {{each-in}} does not unwrap proxies, and conditionals do not read isTruthy from a proxy.

The tests of proxy behavior skip with the flag.

Other fixes

• @ember/service had a side effect when it loaded. A static field now marks the plain class, and the tree-shakability snapshot is the same as on main.
• The legacy computed test failed in the stable decorators job. It read the descriptor before the first instance finalized the class.
• @ember/test-helpers 5.7.0 extends EmberObject at module scope. A pnpm patch creates that class on first use. Delete the patch when Migrate the test-specific Owner to not rely on imminently deprecated features (mixins and EmberObject) ember-test-helpers#1584 ships.

Bundle size

smoke-tests/v2-app-hello-world-template renders one component. Its config sets the flag.

Build	Minified JS
main	129,289 bytes
this PR	116,820 bytes

The hello-world bundle has no CoreObject, EmberObject, mixin, proxy or Namespace code.

It still has the observer code. Query params sync the controller to the URL through internal observers, also for @tracked properties. Removing observers needs a new query param sync first.

smoke-tests/v2-app-template uses classicEmberSupport() and classic dependencies, so its bundle keeps the classic code with the flag.

Checks

On main at 6772f7b, at 465bd0d.

Mode	Result
Default	9285 tests, 0 failures
ALL_DEPRECATIONS_ENABLED=true	9285 tests, 0 failures
OVERRIDE_DEPRECATION_VERSION=15.0.0	8308 tests, 0 failures
Production build	9122 tests, 0 failures
EMBER_DROP_CLASSIC_FEATURES=true	8981 tests, 0 failures
VITE_STABLE_DECORATORS=true	9285 tests, 0 failures
VITE_STABLE_DECORATORS=typescript	9285 tests, 0 failures

The type checks of the internals and of the published types (with and without stable decorators), eslint, prettier, the docs check and the tree-shakability test pass.

Supersedes the old spike #21674.

🤖 Generated with Claude Code