perf: injection tokens' factories don't get tree-shaken

[davidlj95]

After implementing some new APIs that weren't used in any place (except for unit tests of those) in #883, expected that bundle size of production apps wouldn't change. Because those APIs weren't used. So they'd be tree-shaken... right? Well turns out they aren't:

📦 Bundle size (Angular v18)

Git ref: 6709d12f8a4f41b5fa323f1c63c67c3947750af1

Module file	Size	Base size	Difference
ngx-meta-core.mjs	3134 bytes (3.1KiB)	2816 bytes (2.8KiB)	11.29%: 318 bytes (318B)

(Not only v18, but also rest of versions)

So first thought it would have to do with the recent re-organization of files and directories and the index.ts files around exporting module's features. See #862.

Found this evanw/esbuild#1420 But doesn't seem to be the issue as we don't use export * as x. Also tried reverting that change back and the issue still appears again.

However, if we export something like const FOO = 'foo'. It doesn't appear in the production build if unused.

Tried then exporting partially until seeing which is the part that can't get tree shaken. Used the v18 app as reference. Exporting the helpers withNameAttribute, withContentAttribute ... but not using them just adds 4 bytes to the bundle* I was expecting 0, but definitely 4 is something acceptable and probably related to bundler internals.

After checking, seems it's due to var added. Not sure why. Bundler mysteries. Maybe var can't declare at once more than x things at once? Given the output is var x=[...],y=[...],... Anywaysssss

What if the new InjectionToken is the issue? Tried exporting const FOO = new InjectionToken('foo'). It gets in the production bundle despite unused! Why? Probably because new X may come with side effects so it's not 100% to tree shake it.

Tried then removing usages of _HEAD_ELEMENT_UPSERT_OR_REMOVE (standard & json ld modules) from the example app. Built again and... yup, the token and it's factory are still in the production bundle. How can then an injection token be defined in a manner that if it's unused doesn't end up in the production bundle?

[davidlj95]

After introduction of lazy injection tokens, this has been solved. However, some learnings:

• An injection token built with new InjectionToken isn't tree shakeable. It will stay there even if unused.
• Services provided in root are the only Angular'ish way to provide tree-shakeable services for now.
• Lazy injection tokens can be used internally. But it's not something very Angular'ish (yet?). So better to use it internally only.

Lazy injection tokens were introduced in:

• chore: add util to make (lazy) injection tokens #892
• refactor: rename util to lazy injection token #901
• refactor: rename util back to make injection token #903
• refactor: remove test failures/logs from injection token maker #904
• refactor: allow lazy injection tokens not to provide a factory #907

And used around in:

• refactor: use lazy injection token for head utility #902
• refactor: use lazy injection token for JSON metadata resolver #905
• refactor: use lazy injection token for url resolver #906
• refactor: use lazy injection token for defaults #908
• refactor: use lazy injection token for metadata registry #909
• refactor: use lazy injection token for metadata resolver #910
• refactor: use lazy injection token for route metadata strategy #911
• refactor: use lazy injection token for router listener #913