Add failing immutable slice test

crates/web-sys/tests/wasm/element.js

@@ -151,6 +151,11 @@ export function new_title() {
   return document.createElement("title");
 }
 
+export function new_webgl_rendering_context() {
+  const canvas = document.createElement('canvas');
+  return canvas.getContext('webgl');
+}
+
 export function new_xpath_result() {
     let xmlDoc = new DOMParser().parseFromString("<root><value>tomato</value></root>", "application/xml");
     let xpathResult = xmlDoc.evaluate("/root//value", xmlDoc, null, XPathResult.ANY_TYPE, null);

crates/web-sys/tests/wasm/immutable_slices.rs

@@ -0,0 +1,26 @@
+//! When generating our web_sys APIs we default to setting slice references that
+//! get passed to JS as mutable in case they get mutated in JS.
+//!
+//! In certain cases we know for sure that the slice will not get mutated - for
+//! example when working with the WebGlRenderingContext APIs.
+//!
+//! These tests ensure that whitelisted methods do indeed accept mutable slices.
+//!
+//! @see https://github.com/rustwasm/wasm-bindgen/issues/1005
+
+use wasm_bindgen::prelude::*;
+use wasm_bindgen_test::*;
+use web_sys::WebGlRenderingContext;
+
+#[wasm_bindgen(module = "./tests/wasm/element.js")]
+extern "C" {
+    fn new_webgl_rendering_context() -> WebGlRenderingContext;
+}
+
+// Ensure that our whitelisted WebGlRenderingContext methods work
+#[wasm_bindgen_test]
+fn test_webgl_rendering_context_immutable_slices() {
+    let gl = new_webgl_rendering_context();
+
+    gl.vertex_attrib1fv_with_f32_array(0, &[5000.]);
+}

crates/web-sys/tests/wasm/main.rs

@@ -56,6 +56,7 @@ pub mod style_element;
 pub mod table_element;
 pub mod title_element;
 pub mod xpath_result;
+pub mod immutable_slices;
 
 #[wasm_bindgen_test]
 fn deref_works() {

crates/webidl-tests/lib.rs

@@ -1 +1,3 @@
 // intentionally left blank
+
+// QUESTION FOR REVIEWER: WHY? (I'll include this context in the comment)