Use the wasm_bindgen_downcast crate for downcasting JsValues

We need this because @wasmer/wasi gets minified, which breaks our downcast check.

Cargo.lock

@@ -3208,9 +3208,9 @@ checksum = "6bdef32e8150c2a081110b42772ffe7d7c9032b606bc226c8260fd97e0976601"
 
 [[package]]
 name = "syn"
-version = "1.0.103"
+version = "1.0.105"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "a864042229133ada95abf3b54fdc62ef5ccabe9515b64717bcb9a1919e59445d"
+checksum = "60b9b43d45702de4c839cb9b51d9f529c5dd26a4aff255b42b1ebc03e88ee908"
 dependencies = [
  "proc-macro2",
  "quote",
@@ -3815,6 +3815,29 @@ dependencies = [
  "wasm-bindgen-shared",
 ]
 
+[[package]]
+name = "wasm-bindgen-downcast"
+version = "0.1.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "5dac026d43bcca6e7ce1c0956ba68f59edf6403e8e930a5d891be72c31a44340"
+dependencies = [
+ "js-sys",
+ "once_cell",
+ "wasm-bindgen",
+ "wasm-bindgen-downcast-macros",
+]
+
+[[package]]
+name = "wasm-bindgen-downcast-macros"
+version = "0.1.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "c5020cfa87c7cecefef118055d44e3c1fc122c7ec25701d528ee458a0b45f38f"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn",
+]
+
 [[package]]
 name = "wasm-bindgen-futures"
 version = "0.4.33"
@@ -3929,6 +3952,7 @@ dependencies = [
  "thiserror",
  "tracing",
  "wasm-bindgen",
+ "wasm-bindgen-downcast",
  "wasm-bindgen-test",
  "wasmer-compiler",
  "wasmer-compiler-cranelift",

lib/api/Cargo.toml

@@ -62,6 +62,7 @@ macro-wasmer-universal-test = { version = "3.0.2", path = "./macro-wasmer-univer
 # - Mandatory dependencies for `js`.
 wasmer-types = { path = "../types", version = "=3.0.2", default-features = false, features = ["std"] }
 wasm-bindgen = "0.2.74"
+wasm-bindgen-downcast = { version = "0.1.1" }
 js-sys = "0.3.51"
 #web-sys = { version = "0.3.51", features = [ "console" ] }
 wasmer-derive = { path = "../derive", version = "=3.0.2" }

lib/api/src/js/trap.rs

@@ -5,6 +5,7 @@ use std::sync::Arc;
 use wasm_bindgen::convert::FromWasmAbi;
 use wasm_bindgen::prelude::*;
 use wasm_bindgen::JsValue;
+use wasm_bindgen_downcast::DowncastJS;
 
 pub trait CoreError: fmt::Debug + fmt::Display {
     fn source(&self) -> Option<&(dyn CoreError + 'static)> {
@@ -92,7 +93,7 @@ impl dyn CoreError {
 /// A struct representing an aborted instruction execution, with a message
 /// indicating the cause.
 #[wasm_bindgen]
-#[derive(Clone)]
+#[derive(Clone, DowncastJS)]
 pub struct WasmerRuntimeError {
     inner: Arc<RuntimeErrorSource>,
 }
@@ -251,35 +252,12 @@ impl std::error::Error for RuntimeError {
     }
 }
 
-pub fn generic_of_jsval<T: FromWasmAbi<Abi = u32>>(
-    js: JsValue,
-    classname: &str,
-) -> Result<T, JsValue> {
-    use js_sys::{Object, Reflect};
-    let ctor_name = Object::get_prototype_of(&js).constructor().name();
-    if ctor_name == classname {
-        let ptr = Reflect::get(&js, &JsValue::from_str("ptr"))?;
-        match ptr.as_f64() {
-            Some(ptr_f64) => {
-                let foo = unsafe { T::from_abi(ptr_f64 as u32) };
-                Ok(foo)
-            }
-            None => {
-                // We simply relay the js value
-                Err(js)
-            }
-        }
-    } else {
-        Err(js)
-    }
-}
-
 impl From<JsValue> for RuntimeError {
     fn from(original: JsValue) -> Self {
         // We try to downcast the error and see if it's
         // an instance of RuntimeError instead, so we don't need
         // to re-wrap it.
-        generic_of_jsval(original, "WasmerRuntimeError").unwrap_or_else(|js| RuntimeError {
+        WasmerRuntimeError::downcast_js(original).unwrap_or_else(|js| RuntimeError {
             inner: Arc::new(RuntimeErrorSource::Js(js)),
         })
     }