Create Static Enough Metaprogramming proposal

[mraleph]

This moves content from #4271 into a markdown file in the repository to make discussion and revisions easier.

I have incorporated some of the feedback from discussions on the issue - but I continue to maintain focus on this as a toolchain feature. I have added some remarks that analyzer can't constant fold everything anyway because it does not have access to the compilation environment.

I would like to collect a few rounds of feedback and then rejuvenate the prototype implementation to get something experimental working across all platforms in the SDK so that we can have an idea of how well this could work in a real world.

[eernstg]

LGTM. (Very interesting indeed!)

I could suggest the addition of 'a' or 'the' in many locations, but decided that this wouldn't be the top priority at this time.

[jakemac53]

This definitely does drastically simplify the proposal - but it also makes it a lot less useful. Ultimately trying to accomplish this was the downfall of the original macros proposal though.

But, I think it is important to look at the original motivations for macros, and which of those use cases are covered by this.

Ultimately, I think you can end up with some fairly decent solutions for automatic encoding/decoding, equality, toString, etc. But not copyWith or constructors due to the signatures being dependent on the shape of the class (you could generate the bodies of these but that's only half the boilerplate).

Edit: I see you have an interesting copyWith idea using records, that is fairly reasonable actually.

[mraleph]

I have added a section trying to cover some of the use cases mentioned peaked from an old spreadsheet I managed to find.

I could not exactly figure out what some of those entail, could you help me a bit (look for TODO: unclear what this means. and if you have context please add it in the comment). I am interested about auto listenable and render accessors. I think union types (ala freezed) means more concise way of declaring sealed class hierarchies - which I think should just be its own feature (paired with primary constructors).

I think a number of use cases require property wrappers and/or ability to redirect methods - this should probably be its own feature. If property wrappers are available then @konst can be used to handle the boilerplate.

Finally some cases (e.g. proxies, functional widgets and reduced widget classes boilerplate) require ability to create class declarations. I think it is actually an okay feature to give via @konst reflection. As long as classes are anonymous and are otherwise not visible.

[jakemac53]

What is the baseline?

[mraleph]

I don't have numbers right now but I can try to revive the prototype and update this later.

[jakemac53]

This would be 🔥 (and help a lot with the reduction of boilerplate)

[mraleph]

Yeah, it would be useful in many places. Also it would solve a performance problem we occasionally encounter where inheritance or generics cause polymorphism and severely reduce performance.

[mraleph]

I have made some updates based on comments. PTAL.

[munificent]

I still have the same reservations as before, but landing this in the repo so we can discuss more sounds great. It's a very solid well-thought out proposal and the background information it provides is really helpful for any metaprogramming-related features we might do.