Implement To/FromWasmAbi traits for boxed slices of JsValue wrappers

Author: Jules-Bertholet

crates/backend/src/codegen.rs

@@ -624,7 +624,7 @@ impl ToTokens for ast::ImportType {
                 use wasm_bindgen::convert::{OptionIntoWasmAbi, OptionFromWasmAbi};
                 use wasm_bindgen::convert::RefFromWasmAbi;
                 use wasm_bindgen::describe::WasmDescribe;
-                use wasm_bindgen::{JsValue, JsCast};
+                use wasm_bindgen::{JsValue, JsCast, JsObject};
                 use wasm_bindgen::__rt::core;
 
                 impl WasmDescribe for #rust_name {
@@ -761,6 +761,8 @@ impl ToTokens for ast::ImportType {
                     }
                 }
 
+                impl JsObject for #rust_name {}
+
                 ()
             };
         })

src/cast.rs

@@ -1,4 +1,4 @@
-use crate::JsValue;
+use crate::{describe::WasmDescribe, JsValue};
 
 /// A trait for checked and unchecked casting between JS types.
 ///
@@ -154,3 +154,6 @@ where
     /// won't need to call this.
     fn unchecked_from_js_ref(val: &JsValue) -> &Self;
 }
+
+/// Trait implemented for wrappers around `JsValue`s generated by `#[wasm_bindgen]`.
+pub trait JsObject: JsCast + WasmDescribe {}

src/convert/slices.rs

@@ -4,6 +4,7 @@ use std::prelude::v1::*;
 use core::slice;
 use core::str;
 
+use crate::cast::JsObject;
 use crate::convert::OptionIntoWasmAbi;
 use crate::convert::{FromWasmAbi, IntoWasmAbi, RefFromWasmAbi, RefMutFromWasmAbi, WasmAbi};
 use cfg_if::cfg_if;
@@ -270,4 +271,41 @@ if_std! {
         #[inline]
         fn is_none(slice: &WasmSlice) -> bool { slice.ptr == 0 }
     }
+
+    impl<T> IntoWasmAbi for Box<[T]> where T: JsObject {
+        type Abi = WasmSlice;
+
+        #[inline]
+        fn into_abi(self) -> WasmSlice {
+            let ptr = self.as_ptr();
+            let len = self.len();
+            mem::forget(self);
+            WasmSlice {
+                ptr: ptr.into_abi(),
+                len: len as u32,
+            }
+        }
+    }
+
+    impl<T> OptionIntoWasmAbi for Box<[T]> where T: JsObject {
+        #[inline]
+        fn none() -> WasmSlice { null_slice() }
+    }
+
+    impl<T> FromWasmAbi for Box<[T]> where T: JsObject {
+        type Abi = WasmSlice;
+
+        #[inline]
+        unsafe fn from_abi(js: WasmSlice) -> Self {
+            let ptr = <*mut JsValue>::from_abi(js.ptr);
+            let len = js.len as usize;
+            let vec: Vec<T> = Vec::from_raw_parts(ptr, len, len).drain(..).map(|js_value| T::unchecked_from_js(js_value)).collect();
+            return vec.into_boxed_slice();
+        }
+    }
+
+    impl<T> OptionFromWasmAbi for Box<[T]> where T: JsObject {
+        #[inline]
+        fn is_none(slice: &WasmSlice) -> bool { slice.ptr == 0 }
+    }
 }

src/lib.rs

@@ -63,6 +63,7 @@ pub mod describe;
 
 mod cast;
 pub use crate::cast::JsCast;
+pub use crate::cast::JsObject;
 
 if_std! {
     extern crate std;