Remove the stack-machine wasmi engine backend (#818)

* remove EngineBackend and conditionals of users

Also remove tests testing the stack-machine wasmi engine backend which is about to be removed since those tests can no longer be run.

* remove code directly related to the stack-machine backend

No post-removal clean ups performed in this commit.

* fix doclinks and minor renamings

* make caller_results non optional

The None variant was only needed for the removed stack-machine engine backend.

crates/cli/src/args.rs

@@ -1,12 +1,11 @@
-use anyhow::{bail, Context, Error, Result};
+use anyhow::{Context, Error, Result};
 use clap::Parser;
 use std::{
     ffi::OsStr,
     net::SocketAddr,
     path::{Path, PathBuf},
     str::FromStr,
 };
-use wasmi::EngineBackend;
 use wasmi_wasi::{ambient_authority, Dir, TcpListener, WasiCtx, WasiCtxBuilder};
 
 /// A CLI flag value key-value argument.
@@ -37,23 +36,6 @@ impl FromStr for KeyValue {
     }
 }
 
-/// A `wasmi` [`EngineBackend`].
-#[derive(Debug, Clone)]
-pub struct ExecutionEngine(EngineBackend);
-
-impl FromStr for ExecutionEngine {
-    type Err = Error;
-
-    fn from_str(argument: &str) -> Result<Self, Self::Err> {
-        let engine = match argument {
-            "stack-machine" => ExecutionEngine(EngineBackend::StackMachine),
-            "register-machine" => ExecutionEngine(EngineBackend::RegisterMachine),
-            _ => bail!("invalid execution engine: {argument}"),
-        };
-        Ok(engine)
-    }
-}
-
 /// The `wasmi` CLI application arguments.
 #[derive(Parser, Debug)]
 #[clap(author, version, about, long_about = None, trailing_var_arg = true)]
@@ -106,20 +88,6 @@ pub struct Args {
     #[clap(long = "fuel", value_name = "N")]
     fuel: Option<u64>,
 
-    /// Tells `wasmi` which execution engine to use. (EXPERIMENTAL / UNSTABLE)
-    ///
-    /// Valid Arguments:
-    ///
-    /// - stack-machine (default)
-    ///
-    /// - register-machine
-    #[clap(
-        long = "engine",
-        value_name = "ENGINE",
-        value_parser(ExecutionEngine::from_str)
-    )]
-    engine: Option<ExecutionEngine>,
-
     /// Arguments given to the Wasm module or the invoked function.
     #[clap(value_name = "ARGS")]
     func_args: Vec<String>,
@@ -146,11 +114,6 @@ impl Args {
         self.fuel
     }
 
-    /// Returns the execution engine given to the CLI app if any.
-    pub fn engine(&self) -> Option<EngineBackend> {
-        self.engine.as_ref().map(|engine| engine.0)
-    }
-
     /// Pre-opens all directories given in `--dir` and returns them for use by the [`WasiCtx`].
     ///
     /// # Errors

crates/cli/src/context.rs

@@ -1,7 +1,7 @@
 use crate::utils;
 use anyhow::{anyhow, Error};
 use std::path::Path;
-use wasmi::{Config, EngineBackend, ExternType, Func, FuncType, Instance, Module, Store};
+use wasmi::{Config, ExternType, Func, FuncType, Instance, Module, Store};
 use wasmi_wasi::WasiCtx;
 
 /// The [`Context`] for the `wasmi` CLI application.
@@ -23,14 +23,8 @@ impl Context {
     ///
     /// - If parsing, validating, compiling or instantiating the Wasm module failed.
     /// - If adding WASI defintions to the linker failed.
-    pub fn new(
-        wasm_file: &Path,
-        wasi_ctx: WasiCtx,
-        fuel: Option<u64>,
-        engine: EngineBackend,
-    ) -> Result<Self, Error> {
+    pub fn new(wasm_file: &Path, wasi_ctx: WasiCtx, fuel: Option<u64>) -> Result<Self, Error> {
         let mut config = Config::default();
-        config.set_engine_backend(engine);
         if fuel.is_some() {
             config.consume_fuel(true);
         }

crates/cli/src/main.rs

@@ -20,8 +20,7 @@ fn main() -> Result<()> {
     let args = Args::parse();
     let wasm_file = args.wasm_file();
     let wasi_ctx = args.wasi_context()?;
-    let engine = args.engine().unwrap_or_default();
-    let mut ctx = Context::new(wasm_file, wasi_ctx, args.fuel(), engine)?;
+    let mut ctx = Context::new(wasm_file, wasi_ctx, args.fuel())?;
     let (func_name, func) = get_invoked_func(&args, &ctx)?;
     let ty = func.ty(ctx.store());
     let func_args = utils::decode_func_args(&ty, args.func_args())?;

crates/wasmi/benches/bench/mod.rs

@@ -1,5 +1,5 @@
 use std::{fs::File, io::Read as _};
-use wasmi::{Config, EngineBackend, StackLimits};
+use wasmi::{Config, StackLimits};
 
 /// Returns the Wasm binary at the given `file_name` as `Vec<u8>`.
 ///
@@ -25,7 +25,6 @@ pub fn bench_config() -> Config {
     let mut config = Config::default();
     config.wasm_tail_call(true);
     config.set_stack_limits(StackLimits::new(1024, 1024 * 1024, 64 * 1024).unwrap());
-    config.set_engine_backend(EngineBackend::RegisterMachine);
     config
 }