support interned enums

[gvozdvmozgu]

close #1026

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[codspeed-hq]

CodSpeed Performance Report

Merging #1027 will improve performances by 5.73%

_{Comparing gvozdvmozgu:interned-enums (80cae02) with master (a885bb4)}

Summary

⚡ 2 improvements
✅ 11 untouched

Benchmarks breakdown

	Benchmark	BASE	HEAD	Change
⚡	amortized[InternedInput]	2.2 µs	2 µs	+5.73%
⚡	new[InternedInput]	4.5 µs	4.3 µs	+4.8%

[MichaReiser]

Thank you for working on this.

[MichaReiser]

I'm not a 100% sure whether this is possible but I think it should be.

Could we move the synthesized struct definition within the const _: () => { block. It has the advantage that we can auto generate a name for the interned struct

https://github.com/MichaReiser/salsa/blob/0c64a1a99aeb0986b951eb7b1367dac5b1fbb32f/components/salsa-macro-rules/src/setup_interned_struct.rs#L101-L103

[MichaReiser]

Can you add or extend an existing persistence test to show that persistence works with interned enums too

https://github.com/MichaReiser/salsa/blob/0c64a1a99aeb0986b951eb7b1367dac5b1fbb32f/tests/persistence.rs#L4

[MichaReiser]

Hmm, thinking more about this, I don't think this will work, or at least, would be very confusing.

Up to now, a one-argument query can take any salsa-struct (interned, input, or tracked). With this change, this would no longer be the case for interned enums because they don't implement AsId (they can't, they don't know the ID).

I'll close this PR (and the issue) for now as I'm no longer convinced we want this feature. Thanks for giving it a try, it helped me understand why this isn't what we need