Deprecate classic classes (RFC 1117)

[NullVoxPopuli-ai-agent]

extend, reopen and reopenClass now give the deprecate-classic-classes deprecation (RFC 1117). This PR replaces the draft #21580, which conflicts with main.

• RFC: Deprecate Classic Classes rfcs#1117
• Advancement: Advance RFC #1117 "Deprecate Classic Classes" to Stage Ready for Release rfcs#1141

Blocked by

emberjs/ember-test-helpers#1583 must release first. @ember/test-helpers calls EmberObject.extend() at import time, so these CI jobs fail here until then:

• "All deprecations enabled" (both variants)
• "Deprecations as errors" (both variants)
• "Smoke tests with Deprecations Removed"

With that fix put into node_modules by hand, the first two groups pass locally. I did not run the smoke tests locally.

The deprecation

id	deprecate-classic-classes
available	7.5.0
enabled	not yet, the RFC is not Ready for Release
until	8.0.0

These calls deprecate:

• SomeClass.extend(...)
• SomeClass.reopen(...)
• SomeClass.reopenClass(...)
• someInstance.reopen(...)

Internal use

Ember still applies framework mixins to its own classes, for example Observable on EmberObject and ActionHandler on Route. Those call sites use symbol-keyed methods that do not deprecate:

• INTERNAL_EXTEND
• INTERNAL_REOPEN
• INTERNAL_REOPEN_CLASS

This is the pattern of INTERNAL_MIXIN_CREATE from #21577. The symbols live in @ember/-internals/utils/lib/internal-classic-class.ts.

#21580 used helper functions in a new module instead. That module needed an entry in package.json, and it made six more modules fail the tree shaking snapshot. The symbol methods need neither change.

Tests

• Tests of the classic class system have testUnless(DEPRECATIONS.DEPRECATE_CLASSIC_CLASSES.isRemoved) and call expectClassicClassDeprecation().
• Tests of features that stay now use native classes: router service, query params, HistoryLocation, NoneLocation, the router DSL.
• The test harness (internal-test-helpers) uses the internal symbols, because it builds classes from property bags (routerOptions, the -top-level component).

Three additions to internal-test-helpers:

• expectClassicClassDeprecation() expects the deprecation only while it is enabled.
• subclass(specifier, build) on the application test case replaces a registration with a subclass of it. It replaces this.router.reopen(...).
• expectDeprecationQuietly(message) adds no assertion on a match. expectDeprecation adds one assertion for each message, so 21 tests with assert.expect(n) had a different count when the deprecation was enabled.

Local results

All runs have the @ember/test-helpers fix in node_modules.

Run	Tests	Fail
default	9548	0
all deprecations enabled	9548	0
all deprecations enabled, optional features	9550	0
deprecations as errors	8693 (619 skipped)	0
deprecations as errors, optional features	8695 (619 skipped)	0
production build, optional features	9385	0

Also green: pnpm lint, pnpm type-check, pnpm test:node, pnpm test:node:vitest (tree shaking), and pnpm build leaves package.json unchanged.

Not in this PR

• The deprecation guide for deprecations.emberjs.com.
• smoke-tests/node-template still calls .extend() in its helpers. Those tests run without the deprecation.
• The @classic decorator. It is in the ember-classic-decorator addon, not in this repository.

🤖 Generated with Claude Code

[NullVoxPopuli]

probably needs to move to v9, in coordination with RFC#1234

[NullVoxPopuli]

NOTE: this impl is now optional (but would be good for deprecation guides)

due to RFC #1234