Add an unsafe method view_mut_raw (#1850)

* adding .vscode folder to .gitignore

* Adding view_mut_raw to generated arrays

* test populating rust vector from JS  function

* Uint32Array test, need to make it generic

* Add doc + more test cases

* replacing macro-generated tests with generic test function

it is cleaner, safer and better that way

* improving rustdoc

Author: lshlyapnikov

.gitignore

@@ -9,3 +9,4 @@ yarn.lock
 *.d.ts
 /publish
 /publish.exe
+.vscode

crates/js-sys/src/lib.rs

@@ -4792,6 +4792,31 @@ macro_rules! arrays {
                 )
             }
 
+            /// Creates a JS typed array which is a view into wasm's linear
+            /// memory at the specified pointer with specified length.
+            ///
+            /// This function returns a new typed array which is a view into
+            /// wasm's memory. This view does not copy the underlying data.
+            ///
+            /// # Unsafety
+            ///
+            /// Views into WebAssembly memory are only valid so long as the
+            /// backing buffer isn't resized in JS. Once this function is called
+            /// any future calls to `Box::new` (or malloc of any form) may cause
+            /// the returned value here to be invalidated. Use with caution!
+            ///
+            /// Additionally the returned object can be safely mutated,
+            /// the changes are guranteed to be reflected in the input array.
+            pub unsafe fn view_mut_raw(ptr: *mut $ty, length: usize) -> $name {
+                let buf = wasm_bindgen::memory();
+                let mem = buf.unchecked_ref::<WebAssembly::Memory>();
+                $name::new_with_byte_offset_and_length(
+                    &mem.buffer(),
+                    ptr as u32,
+                    length as u32
+                )
+            }
+
             fn raw_copy_to(&self, dst: &mut [$ty]) {
                 let buf = wasm_bindgen::memory();
                 let mem = buf.unchecked_ref::<WebAssembly::Memory>();

crates/js-sys/tests/wasm/Array.js

@@ -0,0 +1,6 @@
+// Used for `Array.rs` tests
+exports.populate_array =  function(arr, start, len) {
+  for (i = 0; i < len; i++) {
+    arr[i] = start + i;
+  }
+};

crates/js-sys/tests/wasm/Array.rs

@@ -1,5 +1,6 @@
 use js_sys::*;
 use std::iter::FromIterator;
+use wasm_bindgen::prelude::*;
 use wasm_bindgen::JsCast;
 use wasm_bindgen::JsValue;
 use wasm_bindgen_test::*;
@@ -466,3 +467,87 @@ fn array_inheritance() {
     assert!(array.is_instance_of::<Object>());
     let _: &Object = array.as_ref();
 }
+
+#[wasm_bindgen(module = "tests/wasm/Array.js")]
+extern "C" {
+    fn populate_array(arr: JsValue, start: JsValue, len: JsValue) -> JsValue;
+}
+
+fn test_array_view_mut_raw<ElemT: std::cmp::PartialEq + std::fmt::Debug, ArrT>(
+    sut: unsafe fn(*mut ElemT, usize) -> ArrT,
+    u8ToElem: fn(u8) -> ElemT,
+    arrToJsValue: fn(ArrT) -> JsValue,
+) {
+    let start: u8 = 10;
+    let len: usize = 32;
+    let end: u8 = start + len as u8;
+    let mut buffer: Vec<ElemT> = Vec::new();
+    buffer.reserve(len);
+    unsafe {
+        let array: ArrT = sut(buffer.as_mut_ptr(), len);
+        populate_array(
+            arrToJsValue(array),
+            JsValue::from(start),
+            JsValue::from(len as u32),
+        );
+        buffer.set_len(len);
+    }
+    let expected: Vec<ElemT> = (start..end).map(u8ToElem).collect();
+    assert_eq!(buffer, expected)
+}
+
+#[wasm_bindgen_test]
+fn Int8Array_view_mut_raw() {
+    fn u8Toi8_unsafe(x: u8) -> i8 {
+        x as i8
+    }
+    test_array_view_mut_raw(
+        js_sys::Int8Array::view_mut_raw,
+        u8Toi8_unsafe,
+        JsValue::from,
+    );
+}
+
+#[wasm_bindgen_test]
+fn Int16Array_view_mut_raw() {
+    test_array_view_mut_raw(js_sys::Int16Array::view_mut_raw, i16::from, JsValue::from);
+}
+
+#[wasm_bindgen_test]
+fn Int32Array_view_mut_raw() {
+    test_array_view_mut_raw(js_sys::Int32Array::view_mut_raw, i32::from, JsValue::from);
+}
+
+#[wasm_bindgen_test]
+fn Uint8Array_view_mut_raw() {
+    test_array_view_mut_raw(js_sys::Uint8Array::view_mut_raw, u8::from, JsValue::from);
+}
+
+#[wasm_bindgen_test]
+fn Uint8ClampedArray_view_mut_raw() {
+    test_array_view_mut_raw(
+        js_sys::Uint8ClampedArray::view_mut_raw,
+        u8::from,
+        JsValue::from,
+    );
+}
+
+#[wasm_bindgen_test]
+fn Uint16Array_view_mut_raw() {
+    test_array_view_mut_raw(js_sys::Uint16Array::view_mut_raw, u16::from, JsValue::from);
+}
+
+#[wasm_bindgen_test]
+fn Uint32Array_view_mut_raw() {
+    test_array_view_mut_raw(js_sys::Uint32Array::view_mut_raw, u32::from, JsValue::from);
+}
+
+#[wasm_bindgen_test]
+fn Float32Array_view_mut_raw() {
+    test_array_view_mut_raw(js_sys::Float32Array::view_mut_raw, f32::from, JsValue::from);
+}
+
+#[wasm_bindgen_test]
+fn Float64Array_view_mut_raw() {
+    test_array_view_mut_raw(js_sys::Float64Array::view_mut_raw, f64::from, JsValue::from);
+}