Make ember-lts-4.12 compat scenario runnable

Three stacked runtime issues were blocking ember-lts-4.12 once the
`require` import issue from ember-cli#321 cleared. All three affect the compat
path (ENABLE_COMPAT_BUILD=true, ember4 deps overrides) and are hidden
for ember-source >= 6 because the upstream code was rewritten.

1. "Cannot read properties of undefined (reading 'has')" at
   `makeComputedDecorator` → `COMPUTED_GETTERS.has(...)`.

   ember-source <= 5.x's `@ember/-internals/metal` has
   `let COMPUTED_GETTERS; if (DEBUG) { COMPUTED_GETTERS = new WeakSet(); }`
   paired with `assert(..., !COMPUTED_GETTERS.has(...))`. `DEBUG` comes
   from `@glimmer/env`, whose published default is `DEBUG = false`.
   Without something resolving `DEBUG` at compile time, rollup tree-shakes
   the init but the `assert` predicate still runs eagerly, so
   `COMPUTED_GETTERS` is undefined at runtime.

   Conditionally add `babel-plugin-debug-macros` (only when
   ENABLE_COMPAT_BUILD is set) with `flags: [{ source: '@glimmer/env',
   flags: { DEBUG: true } }]` so the plugin inlines `DEBUG = true` in
   ember-source. The init and the use stay consistent. Non-compat
   scenarios don't need the plugin — modern ember-source uses
   `isDevelopingApp()` from `@embroider/macros`, which `buildMacros()`
   already handles — so gating on ENABLE_COMPAT_BUILD keeps the default
   build untouched.

2. "ReferenceError: requirejs is not defined" from ember-qunit's
   auto-loadTests.

   ember-qunit@8's `start()` calls `loadTests()` which uses
   `requirejs.entries` — there's no loader.js in a vite build.
   ember-qunit@9 dropped that call entirely. Pass `{ loadTests: false }`
   so `start()` skips the requirejs-based loader; tests/index.html
   already uses `import.meta.glob` to discover them. The option is
   safely ignored by ember-qunit 9.

3. "Cannot read properties of undefined (reading
   '_APPLICATION_TEMPLATE_WRAPPER')" from `@ember/test-helpers`'s `visit`
   and `setup-rendering-context`.

   test-helpers 4.x reads `global.EmberENV._APPLICATION_TEMPLATE_WRAPPER`
   to decide whether to look inside the `.ember-view` wrapper. In
   classic ember-cli apps the global is populated from index.html; here
   we need to set it ourselves from config. Assign `globalThis.EmberENV`
   in `test-helper.js`. test-helpers 5.x no longer reads this at all, so
   the assignment is harmless for non-compat scenarios.

Co-Authored-By: Claude Opus 4.7 (1M context) <[email protected]>

Author: NullVoxPopuli

pnpm-lock.yaml

@@ -4,6 +4,8 @@ import { buildMacros } from '@embroider/macros/babel';
 
 const macros = buildMacros();
 
+const isCompatBuild = !!process.env.ENABLE_COMPAT_BUILD;
+
 export default {
   plugins: [
     [
@@ -44,6 +46,16 @@ export default {
       },
     ],
     ...macros.babelMacros,
+    ...(isCompatBuild
+      ? [
+          [
+            'babel-plugin-debug-macros',
+            {
+              flags: [{ source: '@glimmer/env', flags: { DEBUG: true } }],
+            },
+          ],
+        ]
+      : []),
   ],
 
   generatorOpts: {

test-app/babel.config.mjs

@@ -35,6 +35,7 @@
     "@babel/eslint-parser": "^7.23.3",
     "@babel/plugin-transform-runtime": "^7.29.0",
     "@babel/plugin-transform-typescript": "^7.28.6",
+    "babel-plugin-debug-macros": "^0.3.4",
     "@ember/string": "^4.0.1",
     "@ember/test-helpers": "^5.4.1",
     "@embroider/core": "^4.4.7",

test-app/package.json

@@ -3,11 +3,13 @@ import config, { enterTestMode } from 'test-app/config/environment';
 import { setApplication } from '@ember/test-helpers';
 import { start as qunitStart, setupEmberOnerrorValidation } from 'ember-qunit';
 
+globalThis.EmberENV = config.EmberENV;
+
 export function start() {
   enterTestMode();
   setApplication(Application.create(config.APP));
 
   setupEmberOnerrorValidation();
 
-  qunitStart();
+  qunitStart({ loadTests: false });
 }