Add early exit example

Cargo.toml

@@ -128,6 +128,11 @@ test-no-traps = ["wasmer-wast/test-no-traps"]
 name = "static_and_dynamic_functions"
 harness = false
 
+[[example]]
+name = "early-exit"
+path = "examples/early_exit.rs"
+required-features = ["cranelift"]
+
 [[example]]
 name = "engine-jit"
 path = "examples/engine_jit.rs"

examples/early_exit.rs

@@ -0,0 +1,82 @@
+//! This example shows how the host can terminate execution of Wasm early from
+//! inside a host function called by the Wasm.
+
+use anyhow::bail;
+use std::fmt;
+use wasmer::{imports, wat2wasm, Function, Instance, Module, NativeFunc, RuntimeError, Store};
+use wasmer_compiler_cranelift::Cranelift;
+use wasmer_engine_jit::JIT;
+
+// First we need to create an error type that we'll use to signal the end of execution.
+#[derive(Debug, Clone, Copy)]
+struct ExitCode(u32);
+
+// This type must implement `std::error::Error` so we must also implement `std::fmt::Display` for it.
+impl fmt::Display for ExitCode {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(f, "{}", self.0)
+    }
+}
+
+// And then we implement `std::error::Error`.
+impl std::error::Error for ExitCode {}
+
+// The host function that we'll use to terminate execution.
+fn early_exit() {
+    // This is where it happens.
+    RuntimeError::raise(Box::new(ExitCode(1)));
+}
+
+fn main() -> anyhow::Result<()> {
+    // Let's declare the Wasm module with the text representation.
+    let wasm_bytes = wat2wasm(
+        br#"
+(module
+  (type $run_t (func (param i32 i32) (result i32)))
+  (type $early_exit_t (func (param) (result)))
+  (import "env" "early_exit" (func $early_exit (type $early_exit_t)))
+  (func $run (type $run_t) (param $x i32) (param $y i32) (result i32)
+    (call $early_exit)
+    (i32.add
+        local.get $x
+        local.get $y))
+  (export "run" (func $run)))
+"#,
+    )?;
+
+    let store = Store::new(&JIT::new(&Cranelift::default()).engine());
+    let module = Module::new(&store, wasm_bytes)?;
+
+    let import_object = imports! {
+        "env" => {
+            "early_exit" => Function::new_native(&store, early_exit),
+        }
+    };
+    let instance = Instance::new(&module, &import_object)?;
+
+    // get the `run` function which we'll use as our entrypoint.
+    let run_func: NativeFunc<(i32, i32), i32> =
+        instance.exports.get_native_function("run").unwrap();
+
+    // When we call a function it can either succeed or fail.
+    match run_func.call(1, 7) {
+        Ok(result) => {
+            bail!(
+                "Expected early termination with `ExitCode`, found: {}",
+                result
+            );
+        }
+        // we're expecting it to fail.
+        // we attempt to downcast the error into the error type that we were expecting.
+        Err(e) => match e.downcast::<ExitCode>() {
+            // we found the exit code used to terminate execution.
+            Ok(exit_code) => {
+                println!("Exited early with exit code: {}", exit_code);
+                Ok(())
+            }
+            Err(e) => {
+                bail!("Unknown error `{}` found. expected `ErrorCode`", e);
+            }
+        },
+    }
+}

examples/engine_cross_compilation.rs

@@ -27,16 +27,15 @@ use wasmer_engine_native::Native;
 fn main() -> Result<(), Box<dyn std::error::Error>> {
     // Let's declare the Wasm module with the text representation.
     let wasm_bytes = wat2wasm(
-        r#"
+        br#"
 (module
   (type $sum_t (func (param i32 i32) (result i32)))
   (func $sum_f (type $sum_t) (param $x i32) (param $y i32) (result i32)
     local.get $x
     local.get $y
     i32.add)
   (export "sum" (func $sum_f)))
-"#
-        .as_bytes(),
+"#,
     )?;
 
     // Define a compiler configuration.

examples/wasi.rs

@@ -21,9 +21,9 @@ use wasmer_engine_jit::JIT;
 use wasmer_wasi::WasiState;
 
 fn main() -> Result<(), Box<dyn std::error::Error>> {
-    let wasm_path = format!(
-        "{}/tests/wasi-wast/wasi/unstable/hello.wasm",
-        std::env::var("CARGO_MANIFEST_DIR").unwrap()
+    let wasm_path = concat!(
+        env!("CARGO_MANIFEST_DIR"),
+        "/tests/wasi-wast/wasi/unstable/hello.wasm"
     );
     // Let's declare the Wasm module with the text representation.
     let wasm_bytes = std::fs::read(wasm_path)?;