Implement (element) helper for dynamic tag names (RFC #0389)

[NullVoxPopuli-ai-agent]

Summary

Implements the element helper as specified in RFC #0389, continuing the work started in #21048.

• (element "h1") — renders an <h1> wrapping the block content, with full support for attributes, modifiers, and ...attributes
• (element "") — renders block content without a wrapping element
• (element null) / (element undefined) — renders nothing (<!---->)
• Invalid types (number, boolean, object) throw an assertion in development mode
• Tag name changes trigger teardown/recreation of the element

The helper is available in both loose mode (as a built-in helper) and strict mode (importable from @ember/helper).

Implementation approach

Uses the Glimmer VM's WrappedBuilder with dynamicTag: true and wrapped: true capabilities. The element helper returns a lightweight component definition per tag name:

• Non-empty string: ElementComponentDefinition with a custom ElementComponentManager that provides the tag name via getTagName(). The VM's default template ({{yield}}) is used via asWrappedLayout(), which wraps it with dynamic element open/close opcodes.
• Empty string: Same component but getTagName() returns null, so the WrappedBuilder skips the element and just yields the block.
• null/undefined: A VoidElementComponentDefinition with an empty template (no yield), so nothing is rendered.

Files changed

• packages/@ember/-internals/glimmer/lib/helpers/element.ts — Core implementation
• packages/@ember/-internals/glimmer/lib/resolver.ts — Registered in BUILTIN_HELPERS for loose mode
• packages/@ember/-internals/glimmer/index.ts — Re-export
• packages/@ember/helper/index.ts — Public export for strict mode
• packages/@ember/-internals/glimmer/tests/integration/helpers/element-test.js — 15 tests

Test plan

• Basic rendering with static tag name
• Strict mode rendering via defineComponent with imported element
• Empty string renders content without wrapper
• null and undefined render nothing (<!---->)
• Element modifiers ({{on "click" ...}}) work on the dynamic element
• Same element definition can be rendered multiple times
• Dynamic tag name changes trigger teardown/recreation
• Works as @tag argument with ...attributes
• Validation: requires exactly 1 positional argument
• Validation: rejects named arguments
• Validation: rejects non-string types (number, boolean, object)
• All 8646 existing tests continue to pass
• TypeScript type-checking passes
• ESLint passes

🤖 Generated with Claude Code

[NullVoxPopuli]

Tested on the big app at work, and aside from ember not owning the [Invoke] symbol in Glint, everything worked great

[NullVoxPopuli]

it works: https://test-ember-source-implement.limber-glimdown.pages.dev/edit?c=JYWwDg9gTgLgBAYQuCA7Apq%2BAzKy4DkAAgOYA2oI6UA9AMbKQZYEDcAUKJLHAN5wwoAQzoBrdABM4AXzi58xcpWo1BI0cFQk2nFD35oZcvCEJF0IAEYqQECcGzBqOrtHj90ZC5niz5p4gtrWgALTzBnDnZ0AA9ueAl0bCEAVzJ4OjIhAGdsuAAJTzIIAHVoMilYmEwJPKQUZnd2ODgiNTFJOAYUrDgAXjgABiiWzToob16BgAoASn6APgEQ4GyAOm7egGoBgEYRuAAeavAs6oXmlr5eAGIveGnPSfgCMAJ5nLgAHzAv6WlLlcjmAFgBNCApOAhIQAN3QXQoHSkMDCcEsKRgMEMvF4KNWGwhWH%2BAlA6HWhxoIMB1xo93%2B7GpOLu6AeTyovQI6MxaHecE%2BXy5WNQfwBQJah0FhhgAE8In0AESS1Dy66GeWZYBiFV49ZjCbsmD-BYIRGiClKi5AnG0ln08WqCxgM7oC4AoA&format=gjs

and with single-letter elements https://test-ember-source-implement.limber-glimdown.pages.dev/edit?c=JYWwDg9gTgLgBAYQuCA7Apq%2BAzKy4DkAAgOYA2oI6UA9AMbKQZYEDcAUKJLHAN5wwoAQzoBrdABM4AXzi58xcpWo1BI0cFQk2nFD35oZcvCEJF0IAEYqQECcGzBqOrtHj90ZC5niz5p4gtrWgALTzBnDnZ0AA9ueAl0bCEAVzJ4OjIhAGdsuAAJTzIIAHVoMilYmEwJPKQUZnd2ODgiNTFJOAYUrDgAXjgABiiWzToob16BgAoASn6APgEQ4GyAOm7egGoBgEYRuAAeavAs6oXmlr5eAGIveGnPSfgCMAJ5nLgAHzIv6WlLlcjmQFgBNCApOAhIQAN3QXQoHSkMDCcEsKRgMEMvF4KNWGwhWH%2BAlA6HWhxoIMB10p6Bg-3Y1JxdzpcEeXiovQI6MxaHecE%2BXxifwBQJahxiAgAnhE%2BgAiHlY1By66GOWZYBiFV49ZjCac%2BnSBYIRGiCkxC5AnG0w2XCknMBndAXAFAA&format=gjs