Implementing Wasm Proposals - Wasmtime

# Implementing WebAssembly Proposals

## Adding New Support for a Wasm Proposal

The following checkboxes enumerate the steps required to add support for a new WebAssembly proposal to Wasmtime. They can be completed over the course of multiple pull requests.

- Implement support for the proposal in the `wasm-tools` repository. (example)

  - `wast` - text parsing
  - `wasmparser` - binary decoding and validation
  - `wasmprinter` - binary-to-text
  - `wasm-encoder` - binary encoding
  - `wasm-smith` - fuzz test case generation

- Update Wasmtime to use these `wasm-tools` crates, but leave the new proposal unimplemented for now (implementation comes in subsequent PRs). (example)

- Add `Config::wasm_your_proposal` to the `wasmtime` crate.

- Implement the proposal in `wasmtime`, gated behind this flag.

- Add `-Wyour-proposal` to the `wasmtime-cli-flags` crate.

- Update `tests/wast.rs` to spec tests should pass for this proposal.

- Write custom tests in `tests/misc_testsuite/*.wast` for this proposal.

- Enable the proposal in the fuzz targets.

  - Write a custom fuzz target, oracle, and/or test case generator for fuzzing this proposal in particular.

    > For example, we wrote a custom generator, oracle, and fuzz target for exercising `table.{get,set}` instructions and their interaction with GC while implementing the reference types proposal.

- Expose the proposal's new functionality in the `wasmtime` crate's API.

  > For example, the bulk memory operations proposal introduced a `table.copy` instruction, and we exposed its functionality as the `wasmtime::Table::copy` method.

- Expose the proposal's new functionality in the C API.

  > This may require extensions to the standard C API, and if so, should be defined in `wasmtime.h` and prefixed with `wasmtime_`.

- Update `docs/stability-tiers.md` with an implementation status of the proposal.

For information about the status of implementation of various proposals in Wasmtime see the associated documentation.

## Adding component functionality to WASI

The cap-std repository contains crates which implement the capability-based version of the Rust standard library and extensions to that functionality. Once the functionality has been added to the relevant crates of that repository, they can be added into wasmtime by including them in the preview2 directory of the wasi crate.

Currently, WebAssembly modules which rely on preview2 ABI cannot be directly executed by the wasmtime command. The following steps allow for testing such changes.

1. Build wasmtime with the changes `cargo build --release`

2. Create a simple Webassembly module to test the new component functionality by compiling your test code to the `wasm32-wasip1` build target.

3. Build the wasi-preview1-component-adapter as a command adapter. `cargo build -p wasi-preview1-component-adapter --target wasm32-wasip1 --release --features command --no-default-features`

4. Use wasm-tools to convert the test module to a component. `wasm-tools component new --adapt wasi_snapshot_preview1=wasi_snapshot_preview1.command.wasm -o component.wasm path/to/test/module`

5. Run the test component created in the previous step with the locally built wasmtime. `wasmtime -W component-model=y -S preview2=y component.wasm`