Bug introduced by #574 when using conditional importSync

[simonihmig]

Reproduction: https://github.com/simonihmig/eai-cached-decorator-polyfill-reproduction

What's happening:

• An app with latest eai uses the v2 addon ember-headless-table
• ember-headless-table supports older Ember versions, so uses ember-cached-decorator-polyfill for @cached support
• but it declares only an optional peer dependency on it. So apps on newer Ember version can omit this.
• it does so by applying the polyfill's babel plugin to its own code as part of its own (publish-time) build
• the static v2 code in /dist looks like this:

  let cached = macroCondition(dependencySatisfies('ember-source', '>= 4.1.0-alpha.0')) ? importSync('@glimmer/tracking').cached : importSync('ember-cached-decorator-polyfill').cached;
  

• when the app builds, this code is transformed by @embroider/macros to:

  let cached=(0,_embroider_macros_src_addon_runtime__WEBPACK_IMPORTED_MODULE_1__.macroCondition)(true)?(0,_embroider_macros_src_addon_es_compat__WEBPACK_IMPORTED_MODULE_0__[\"default\"])(__webpack_require__(/*! @glimmer/tracking */ \"@glimmer/tracking\")).cached:(0,_embroider_macros_src_addon_es_compat__WEBPACK_IMPORTED_MODULE_0__[\"default\"])(__webpack_require__(/*! ember-cached-decorator-polyfill */ \"ember-cached-decorator-polyfill\")).cached;
  

  This is a non-production build, so still contains some runtime stuff. But you see the macroCondition() condition compiled to true, so it will import from @glimmer/tracking rather than ember-cached-decorator-polyfill
• so far everything seems fine...
• But, the AMD shim that eai generates looks (shortened) like this:

  d('ember-headless-table', [..., 'ember-cached-decorator-polyfill', ...], function() { ... })
  

• in the browser, this then fails with Error: Could not find module ember-cached-decorator-polyfill imported from ember-headless-table

This was revealed in a renovate PR updating our app to eai to 2.6.3. When we still had ember-cached-decorator-polyfill, this didn't show up (but another problem - @ef4 this was the state of the PR when you looked into it back then). So now after removing ember-cached-decorator-polyfill, eai 2.6.3 (and not older versions!) causes that error.

I think it must have to do with #574, which changed the way how dependencies from v2 addons (here: ember-headless-table) to v1 addons (here: ember-cached-decorator-polyfill) are handled.

I wonder how we can deal with that issue? Do we have to make the dependencies checker here so smart that it will understand what @embroider/macros do, and that our importSync('ember-cached-decorator-polyfill') is actually dead code and needs to be ignored? 🤔

/cc @NullVoxPopuli

[ef4]

Discussed at embroider weekly meeting, we plan to fix this particular case by making macroCondition sensitive to whether its predicate actually needs a runtime implementation or not. dependencySatisfies does not, so we could do the branch elimination even in dev.

(This is not a generation solution to importSync forcing optional deps to be non-optional, but it covers a very common case)