Blog post: Changes to Rust's WASI targets

posts/2024-04-09-updates-to-rusts-wasi-targets.md

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+---
+layout: post
+title: Changes to Rust's WASI targets
+author: Yosh Wuyts
+---
+
+[WASI 0.2 was recently
+stabilized](https://bytecodealliance.org/articles/WASI-0.2), and Rust has begun
+implementing first-class support for it in the form of a dedicated new target.
+Rust 1.78 will introduce new `wasm32-wasip1` (tier 2) and `wasm32-wasip2` (tier
+3) targets. `wasm32-wasip1` is an effective rename of the existing `wasm32-wasi`
+target, freeing the target name up for an eventual WASI 1.0 release. **Starting
+Rust 1.78 (May 2nd, 2024), users of WASI 0.1 are encouraged to begin migrating
+to the new `wasm32-wasip1` target before the existing `wasm32-wasi` target is
+removed in Rust 1.84 (January 5th, 2025).**
+
+In this post we'll discuss the introduction of the new targets, the motivation
+behind it, what that means for the existing WASI targets, and a detailed
+schedule for these changes. This post is about the WASI targets only; the
+existing `wasm32-unknown-unknown` and `wasm32-unknown-emscripten` targets are
+unaffected by any changes in this post.
+
+## Introducing `wasm32-wasip2`
+
+After nearly five years of work the [WASI 0.2 specification](https://wasi.dev)
+was recently stabilized. This work builds on [WebAssembly
+Components](https://component-model.bytecodealliance.org) (think: strongly-typed
+ABI for Wasm), providing standard interfaces for things like asynchronous IO,
+networking, and HTTP. This will finally make it possible to write asynchronous
+networked services on top of WASI, something which wasn't possible using WASI
+0.1.
+
+People interested in compiling Rust code to WASI 0.2 today are able to do so
+using the [cargo-component](https://github.com/bytecodealliance/cargo-component)
+tool. This tool is able to take WASI 0.1 binaries, and transform them to WASI 0.2
+Components using a shim. It also provides native support for common cargo
+commands such as `cargo build`, `cargo test`, and `cargo run`. While it
+introduces some inefficiencies because of the additional translation layer, in
+practice this already works really well and people should be enough able to get
+started with WASI 0.2 development.
+
+We're however keen to begin making that translation layer obsolete. And for
+that reason we're happy to share that Rust has made its first steps towards
+that with the introduction of the [tier
+3](https://doc.rust-lang.org/rustc/platform-support.html#tier-3) `wasm32-wasip2`
+target landing in Rust 1.78. **This will initially miss a lot of expected**
+**features such as stdlib support, and we don't recommend people use this target**
+**quite yet.** But as we fill in those missing features over the coming months, we
+aim to eventually hit meet the criteria to become a tier 2 target, at which
+point the `wasm32-wasip2` target would be considered ready for general use. This
+work will happen through 2024, and we expect for this to land before the end of
+the calendar year.
+
+## Renaming `wasm32-wasi` to `wasm32-wasip1`
+
+The original name for what we now call WASI 0.1 was "WebAssembly System
+Interface, snapshot 1". Rust shipped support for this in 2019, and we did so
+knowing the target would likely undergo significant changes in the future. With
+the knowledge we have today though, we would not have chosen to introduce the
+"WASI, snapshot 1" target as `wasm32-wasi`. We should have instead chosen to add
+some suffix to the initial target triple so that the eventual stable WASI 1.0
+target can just be called `wasm32-wasi`.
+
+In anticipation of both an eventual WASI 1.0 target, and to preserve consistency
+between target names, we'll begin rolling out a name change to the existing WASI
+0.1 target. Starting in Rust 1.78 (May 2nd, 2024) a new `wasm32-wasip1` target
+will become available. Starting Rust 1.81 (September 5th, 2024) we will begin
+warning existing users of `wasm32-wasi` to migrate to `wasm32-wasip1`. And
+finally in Rust 1.84 (January 9th, 2025) the `wasm32-wasi` target will no longer
+be shipped on the stable release channel. This will provide an 8 month
+transition period for projects to switch to the new target name when they update
+their Rust toolchains.
+
+The name `wasip1` can be read as either "WASI (zero) point one" or "WASI preview
+one". The official specification uses the "preview" moniker, however in most
+communication the form "WASI 0.1" is now preferred. This target triple was
+chosen because it not only maps to both terms, but also more closely resembles
+the target terminology used in [other programming
+languages](https://go.dev/blog/wasi). This is something the WASI Preview 2
+specification [also makes note
+of](https://github.com/WebAssembly/WASI/tree/f45e72e5294e990c23d548eea32fd35c80525fd6/preview2#introduction).
+
+## Timeline
+
+This table provides the dates and cut-offs for the target rename from
+`wasm32-wasi` to `wasm32-wasip1`. The dates in this table do not apply to the
+newly-introduced `wasm32-wasi-preview1-threads` target; this will be renamed to
+`wasm32-wasip1-threads` in Rust 1.78 without going through a transition period.
+The tier 3 `wasm32-wasip2` target will also be made available in Rust 1.78.
+
+| date       | Rust Stable | Rust Beta | Rust Nightly | Notes                                    |
+| ---------- | ----------- | --------- | ------------ | ---------------------------------------- |
+| 2024-02-08 | 1.76        | 1.77      | 1.78         | `wasm32-wasip1` available on nightly     |
+| 2024-03-21 | 1.77        | 1.78      | 1.79         | `wasm32-wasip1` available on beta        |
+| 2024-05-02 | 1.78        | 1.79      | 1.80         | `wasm32-wasip1` available on stable      |
+| 2024-06-13 | 1.79        | 1.80      | 1.81         | warn if `wasm32-wasi` is used on nightly |
+| 2024-07-25 | 1.80        | 1.81      | 1.82         | warn if `wasm32-wasi` is used on beta    |
+| 2024-09-05 | 1.81        | 1.82      | 1.83         | warn if `wasm32-wasi` is used on stable  |
+| 2024-10-17 | 1.82        | 1.83      | 1.84         | `wasm32-wasi` unavailable on nightly     |
+| 2024-11-28 | 1.83        | 1.84      | 1.85         | `wasm32-wasi` unavailable on beta        |
+| 2025-01-09 | 1.84        | 1.85      | 1.86         | `wasm32-wasi` unavailable on stable      |
+
+## Conclusion
+
+In this post we've discussed the upcoming updates to Rust's WASI targets. Come
+Rust 1.78 the `wasm32-wasip1` (tier 2) and `wasm32-wasip2` (tier 3) targets will
+be added. In Rust 1.81 we will begin warning if `wasm32-wasi` is being used. And
+in Rust 1.84, the existing `wasm32-wasi` target will be removed. This will free
+up `wasm32-wasi` to eventually be used for a WASI 1.0 target. Users will have 8
+months to switch to the new target name when they update their Rust toolchains.
+
+The `wasm32-wasip2` target marks the start of native support for WASI 0.2. In
+order to target it today from Rust, people are encouraged to use
+[cargo-component](https://github.com/bytecodealliance/cargo-component) tool
+instead. The plan is to eventually graduate `wasm32-wasip2` to a tier-2 target,
+at which point `cargo-component` will be upgraded to support it natively instead.
+
+With WASI 0.2 finally stable, it's an exciting time for WebAssembly development.
+We're happy for Rust to begin implementing native support for WASI 0.2, and
+we're excited for what this will enable people to build.