[dmcnamara-eng]

Summary

ember-headlessui can't be used in an app on Ember 7.4. ember-source@7 no longer ships dist/ember-template-compiler.js, so every v1 addon in our tree that uses ember-cli-htmlbars ≤ 6 crashes the build:

TypeError: Cannot read properties of undefined (reading 'templateCompiler')
    at Class.templateCompilerPath (ember-cli-htmlbars@6.3.0/lib/ember-addon-main.js:271:32)

Dependency	Before	After	Why
ember-cli-htmlbars	^6.0.1	^7.0.1	v7 resolves the Ember 7 template compiler
ember-element-helper	^0.6.0	^0.8.8	0.6 depends on ember-cli-htmlbars@6
ember-concurrency	^2.1.2	^5.3.0	2.x depends on ember-cli-htmlbars@5; 4.x imports 'ember', which Ember 7 removed
tracked-maps-and-sets	^3.0.1	removed → tracked-built-ins ^4.1.2	its polyfill depends on ember-cli-htmlbars@5
ember-cli-babel	^7.26.3	^8.3.2 (+ @babel/core)	raise the floor
ember-truth-helpers	^3.0.0	^5.0.0	raise the floor (v2 addon, needs Ember ≥ 4.8)
ember-set-helper	^2.0.1	^3.1.0	raise the floor (v2 addon)
ember-modifier	^4.0.0-beta.1	^4.3.0	move off the beta
ember-auto-import	^2.2.0	^2.10.0	raise the floor
@embroider/macros	–	^1.19.0	tracked-built-ins@4 uses appEmberSatisfies (added in 1.19)

Other changes:

• ember-concurrency 5 has no decorators. The 5 @dropTask/@restartableTask generator methods in menu.js, transition/applied-class-names.js and transition/transition-visibility.js are rewritten as task({ drop|restartable: true }, async () => {}). index.js registers ember-concurrency/async-arrow-task-transform.
• Dev tooling: TypeScript 4.7 → 5.9 and added @types/ember__owner, because ember ts:precompile (prepack) can't read the .ts-extension declarations in ember-modifier ≥ 4.2. test-app also gets ember-auto-import ^2.10 and ember-source ~4.8.
• README: new Compatibility table.

⚠️ Breaking

• ember-source ≥ 4.8 (was ≥ 4.4). This comes from ember-truth-helpers@5. The ember-lts-4.4 ember-try scenario and CI job are removed.
• Node ≥ 20, required by ember-cli-htmlbars@7. Volta is now pinned to Node 22.22.2 in the root, addon and test-app.
• Suggest releasing this as 0.18.0, which is what the README table assumes.

Note on CI coverage

The ember-release/ember-beta/ember-canary jobs aren't testing those versions. On the latest master run, the ember-release job's dependency table shows ember-source 4.4.5, because ember-try doesn't actually swap ember-source inside the pnpm workspace. So CI has never covered Ember 5+. Fixing that is out of scope here, which is why Ember 7.4 was verified by hand (below).

Test plan

• pnpm install from a clean node_modules, then pnpm lint: 0 errors (6 pre-existing no-down-event-binding warnings).
• pnpm test (test-app on Ember 4.8.6): 407 tests, 354 pass, 0 fail, 18 skip, 35 todo. The pass/fail counts match master's CI.
• pnpm pack (runs ts:precompile) succeeds.
• Ember 7.4.0 smoke test. Fresh ember-cli@7.3.0 Vite/Embroider app with ember-source@7.4.0:
  • published ember-headlessui@0.17.3: build fails with the templateCompiler error above.
  • this branch (pnpm pack tarball): builds. A rendering test passes 6/6:
    • Menu open, plus typeahead via searchTask
    • Transition hide via unmountAfterTransitionTask/transitionToHide
    • Listbox open
    • Combobox, Switch, Transition and Dialog render
• Not verified: a classic (non-Embroider) ember-cli build on Ember 7.4.

🤖 Generated with Claude Code