Merge pull request #1433 from rust-lang/wasip2-2-electric-boogaloo

Post: The `wasm32-wasip2` target has reached tier 2 support (attempt 2)

Author: Mark-Simulacrum

posts/2024-11-26-wasip2-tier-2.md

@@ -0,0 +1,99 @@
+---
+layout: post
+title: "The wasm32-wasip2 Target Has Reached Tier 2 Support"
+author: Yosh Wuyts
+---
+
+## Introduction
+
+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
+`rust-lang/rustc`, it was not guaranteed to build. We're pleased to announce
+that this has changed in Rust 1.82.
+
+For those unfamiliar with WebAssembly (Wasm) components and WASI 0.2, here is a quick, simplified primer:
+
+- **Wasm** is a (virtual) instruction format for programs to be compiled into (think: x86).
+- **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 1.82 (2024-10-17) the `wasm32-wasip2` (WASI 0.2) target has
+reached tier-2 platform support in the Rust compiler. Among other things this
+now means it is guaranteed to build, and is now available to install 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 always have to rely on tools (such as
+[cargo-component]) which target the WASI 0.1 target (`wasm32-wasip1`) and
+package it into a WASI 0.2 Component via a post-processing step invoked. Now
+that `wasm32-wasip2` is available to everyone via Rustup, tooling can
+begin to directly target WASI 0.2 without the need for additional post-processing.
+
+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
+}
+```
+
+To target the older WASI 0.1 target, Rust also accepts `target_env = "p1"`.
+
+## Standard Library Support
+
+The WASI 0.2 Rust target reaching tier 2 platform support is in a way just the
+beginning. means it's supported and stable. While the platform itself is now
+stable, support in the stdlib for WASI 0.2 APIs is still limited. While the WASI
+0.2 specification specifies APIs for example for timers, files, and sockets - if
+you try and use the stdlib APIs for these today, you'll find they don't yet
+work.
+
+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
+[rust-lang/rust#129638](https://github.com/rust-lang/rust/pull/129638) adding
+native support for `std::net` in Rust 1.83. We expect more of these PRs to land
+through the remainder of the year.
+
+Though this doesn't need to stop users from using WASI 0.2 today. The stdlib is
+great because it provides *portable* abstractions, usually built on top of an
+operating system's `libc` or equivalent. If you want to use WASI 0.2 APIs
+directly today, you can either use the
+[wasi](https://docs.rs/wasi/latest/wasi/) crate directly. Or generate your own
+WASI bindings from the [WASI
+specification's](https://github.com/WebAssembly/WASI/tree/main/wasip2) interface
+types using [wit-bindgen](https://github.com/bytecodealliance/wit-bindgen/).
+
+## Conclusion
+
+The `wasm32-wasip2` target is now installable via Rustup. This makes it possible
+for the Rust compiler to directly compile to the Wasm Components format
+targeting the WASI 0.2 interfaces. There is now also a way for crates to compile
+add WASI 0.2 platform support by writing:
+
+```rust
+#[cfg(all(target_os = "wasi", target_env = "p2"))]
+mod wasip2 {}
+```
+
+We're excited for Wasm Components and WASI 0.2 to have reached this milestone
+within the Rust project, and are excited to see what folks in the community will
+be building with it!