expose wasm intrinsics using target_family = "wasm"

[devsnek]

I think it should be idiomatic to use target_family = "wasm" instead of target_arch = "wasmNN", so we encourage the ecosystem to write code that works for both. This makes it easier to do that by exporting a wasm in addition to wasm32 and wasm64.

[rust-highfive]

Thanks for the pull request, and welcome! The Rust team is excited to review your changes, and you should hear from @Amanieu (or someone else) soon.

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[devsnek]

thanks!

[alexcrichton]

Personally I don't think that this should happen. Even x86/x86_64 don't have precedent for this which is my main personal rationale, but otherwise this is also a new insta-stable module (which I'm not sure was intended?)

[Amanieu]

Oh whoops, I missed the fact that this was marked as insta-stable.

[bjorn3]

Even x86/x86_64 don't have precedent for this which is my main personal rationale

x86 and x86_64 have a different instruction set. wasm32 and wasm64 use the exact same instruction set. AFAIK it is even possible to get a mix of the two by having more than one linear memory. LLVM currently doesn't support this AFAIK, but it could by using different address space's for each linear memory.

[ehuss]

This is causing a problem for wasm32-unknown-emscripten which is in the unix family, but lines above try to import the wasm32 module using target_arch = "wasm32". Should the module include wasm32` in the cfg? Or should this PR be reverted?

[CryZe]

It sounds more like emscripten should be in that family instead to me. It looks like emscripten accidentally overwrites the families here instead of appending to the wasm base's families: https://github.com/rust-lang/rust/blob/master/compiler/rustc_target/src/spec/wasm32_unknown_emscripten.rs#L40

[alexcrichton]

@ehuss looks like the failure came through at rust-lang/rust#90382 (comment), I added another commit to add wasm to the families of emscripten and if that fails I'll dig further and actually build it locally.