wasmtime-wizer 45.0.1

The WebAssembly Pre-Initializer
Documentation 
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use wasmtime::Result;
use wasmtime::{Instance, Linker, Module};
use wasmtime_wizer::Wizer;
use wat::parse_str as wat_to_wasm;

const PRELOAD1: &'static str = r#"
(module
 (func (export "f") (param i32) (result i32)
  local.get 0
  i32.const 1
  i32.add))
  "#;

const PRELOAD2: &'static str = r#"
(module
 (func (export "f") (param i32) (result i32)
  local.get 0
  i32.const 2
  i32.add))
  "#;

async fn run_with_preloads(args: &[wasmtime::Val], wat: &str) -> Result<wasmtime::Val> {
    let wasm = wat_to_wasm(wat)?;
    let engine = wasmtime::Engine::default();
    let mut store = wasmtime::Store::new(&engine, ());
    let mod1 = Module::new(store.engine(), PRELOAD1)?;
    let mod2 = Module::new(store.engine(), PRELOAD2)?;

    let processed = Wizer::new()
        .run(&mut store, &wasm, async |store, module| {
            let i1 = Instance::new_async(&mut *store, &mod1, &[]).await?;
            let i2 = Instance::new_async(&mut *store, &mod2, &[]).await?;
            let mut linker = Linker::new(store.engine());
            linker.instance(&mut *store, "mod1", i1)?;
            linker.instance(&mut *store, "mod2", i2)?;
            linker.instantiate_async(store, module).await
        })
        .await?;

    let testmod = wasmtime::Module::new(&engine, &processed[..])?;

    let mod1_inst = wasmtime::Instance::new_async(&mut store, &mod1, &[]).await?;
    let mod2_inst = wasmtime::Instance::new_async(&mut store, &mod2, &[]).await?;
    let mut linker = wasmtime::Linker::new(&engine);
    linker.instance(&mut store, "mod1", mod1_inst)?;
    linker.instance(&mut store, "mod2", mod2_inst)?;

    let inst = linker.instantiate_async(&mut store, &testmod).await?;
    let run = inst
        .get_func(&mut store, "run")
        .ok_or_else(|| wasmtime::format_err!("no `run` function on test module"))?;
    let mut returned = vec![wasmtime::Val::I32(0)];
    run.call_async(&mut store, args, &mut returned).await?;
    Ok(returned[0])
}

#[tokio::test]
async fn test_preloads() {
    const WAT: &'static str = r#"
    (module
     (import "mod1" "f" (func $mod1f (param i32) (result i32)))
     (import "mod2" "f" (func $mod2f (param i32) (result i32)))
     (global $g1 (mut i32) (i32.const 0))
     (global $g2 (mut i32) (i32.const 0))
     (func (export "wizer-initialize")
      i32.const 100
      call $mod1f
      global.set $g1
      i32.const 100
      call $mod2f
      global.set $g2)
     (func (export "run") (param i32 i32) (result i32)
      local.get 0
      call $mod1f
      local.get 1
      call $mod2f
      i32.add
      global.get $g1
      global.get $g2
      i32.add
      i32.add))
    "#;

    let result = run_with_preloads(&[wasmtime::Val::I32(200), wasmtime::Val::I32(201)], WAT)
        .await
        .unwrap();
    assert!(matches!(result, wasmtime::Val::I32(607)));
}