Merge pull request #1391 from rust-lang/wasip2-tier-2

Post: The wasm32-wasip2 target has reached tier 2 support

Author: BoxyUwU

posts/2024-09-05-wasip2-tier-2.md

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+---
+layout: post
+title: "The wasm32-wasip2 Target Has Reached Tier 2 Support"
+author: Yosh Wuyts
+---
+
+In April of this year we posted an update about [Rust's WASI
+targets](https://blog.rust-lang.org/2024/04/09/updates-to-rusts-wasi-targets.html)
+to the main Rust blog. In it we covered the rename of the `wasm32-wasi` target
+to `wasm32-wasip1`, and the introduction of the new `wasm32-wasip2` target as a
+"tier 3" target. This meant that while the target was available as part of
+`rustc`, it was not guaranteed to build. We're pleased to announce
+that this is changing.
+
+For those unfamiliar with WebAssembly (Wasm) components and WASI 0.2, here is a
+quick, simplified primer:
+
+- **Core Wasm** is a (virtual) instruction format for programs to be compiled into (think: x86-64).
+- **Wasm components** are a container format and type system that wrap Core Wasm instructions into typed, hermetic binaries and libraries (think: ELF).
+- **WASI** is a reserved namespace for a collection of standardized Wasm component interfaces (think: POSIX header files).
+
+For a more detailed explanation see the [WASI 0.2 announcement
+post](https://bytecodealliance.org/articles/WASI-0.2) on the Bytecode Alliance
+blog.
+
+## What's new?
+
+Starting Rust 1.81 (2024-09-05) the `wasm32-wasip2` (WASI 0.2) target will be
+made available as a tier-2 target. Among other things this now means it is
+guaranteed to build, and will become available to install as a prebuilt target
+via Rustup using the following command:
+
+```bash
+rustup target add wasm32-wasip2
+```
+
+Up until now Rust users writing [Wasm
+Components](https://component-model.bytecodealliance.org) would use tools (like
+[cargo-component]) which target the WASI 0.1 target (`wasm32-wasip1`) which
+would be packaged into a WASI 0.2 Component by a post-processing step invoked
+separately by the tooling. With the introduction of `wasm32-wasip2` as a tier-2
+target, that tooling can instead directly target WASI 0.2 without the need for
+additional tooling or compat shims.
+
+What this also means is that ecosystem crates can begin targeting WASI 0.2
+directly for platform-specific code. WASI 0.1 did not have support for sockets.
+Now that we have a stable tier 2 platform available, crate authors should be
+able to finally start writing WASI-compatible network code. To target WASI 0.2
+from Rust, authors can use the following `cfg` attribute:
+
+[cargo-component]: https://github.com/bytecodealliance/cargo-component
+
+```rust
+#[cfg(all(target_os = "wasi", target_env = "p2"))]
+mod wasip2 {
+    // items go here
+}
+```
+
+## What's next?
+
+The WASI 0.2 Rust target being on tier 2 means it's supported and stable. But
+unfortunately it is also still incomplete. Most notably stdlib support is still
+limited. To target platform-native functionality we recommend to either use the
+[wasi](https://docs.rs/wasi/latest/wasi/) crate directly, which is the WASI
+equivalent to the `libc` crate. Or else generate their own bindings to the [WASI
+specifications](https://github.com/WebAssembly/WASI/tree/main/wasip2) using the
+[wit-bindgen](https://github.com/bytecodealliance/wit-bindgen/) generator.
+
+We expect to gradually extend the Rust stdlib with support for WASI 0.2 APIs
+throughout the remainder of this year into the next. That work has already
+started, with for example
+[rust-lang/rust#129638](https://github.com/rust-lang/rust/pull/129638) adding
+native support for `std::net` to WASI 0.2. We expect more of these PRs to land
+through the remainder of the year.
+
+## Conclusion
+
+The `wasm32-wasip2` target will become installable via rustup starting Rust
+1.81.0 (2024-09-05). This will make it possible for the Rust compiler to
+directly compile to the Wasm Components format, targeting the WASI 0.2
+interfaces. We're excited for Wasm Components and WASI 0.2 to have reached this
+milestone, and are excited to see what folks in the ecosystem will be building
+with it!