> something I was doing with my "strict MVP" build of Anubis' WASM wasn't in fact sticking to just the MVP features of WebAssembly
Fun fact, this _used_ to be the case - wasm32-unknown-unknown had extra non-mvp features added later, which in my eyes has been a breaking change on stable. You're not the first person to have been bitten by this, there's [1] and a similar story in Ruffle [2].
Weirdly, the response from the rustc side (IIRC we also talked with one of the devs of wasm component on discord a bit around 2024) has contained a lot of (paraphrasing) "in retrospect we think wasm32-unknown-unknown target was designed badly*, so we'd prefer if you either dealt with it or switched to another wasm target <with its different set of downsides> than us fixing it". (*I acknowledge that the way std was implemented on that target was unusual and "not clean", but it works _really well_ for a lot of people.)
> I looked into the process involved for rebuilding the standard library twice: once with only MVP wasm features enabled and once with an "all yes config" like usual. Based on some research I did this seemed like a massive pain.
That's what Ruffle does [3], it's a bit unfortunate but wouldn't call it a massive pain.
[1] https://internals.rust-lang.org/t/can-we-have-either-a-new-t...
[2] https://github.com/ruffle-rs/ruffle/pull/18397
[3] See lines 55 and 117-127 in https://github.com/ruffle-rs/ruffle/blob/6890c618daab3153343...
> Weirdly, the response from the rustc side (IIRC we also talked with one of the devs of wasm component on discord a bit) has contained a lot of (paraphrasing) "in retrospect we think wasm32-unknown-unknown target was designed badly, so we'd prefer if you either dealt with it or switched to another wasm target <with its different set of downsides> than us fixing it". (I acknowledge that the way std was implemented on that target was unusual and "not clean", but it works _really well_ for a lot of people.)
That's about right. Specifically, wasm32-unknown-unknown is serving multiple targets, which aren't very compatible, and it implements std by panicking in all the bits that can't work.
One target is "you truly have absolutely nothing, and don't really have much of `std` at all". Another target is "you're in a browser, and can do anything a typical browser can provide" (ideally targeting the future where wasm has full browser APIs without going through javascript). Another target is "hosted environment that isn't a browser, and which capabilities you have depends on the environment". Those are three very different things.
I would argue that we need at least two new targets, possibly three:
- `wasm32-none` or similar (by analogy with `x86_64-unknown-none`), a target where you don't have anything except for what you bring with you. The equivalent of writing kernel code.
- `wasm32-wasi-hosted` (or pick another name), where you the hoster of the wasm can supply whatever capabilities you have available.
- `wasm32-wasi-browser`.
It's possible that `none` could be a special case of `hosted`, where the services you provide are "none".