Bug 1921084 - feat(webgpu): wire up WGPU's WGSL lang. features to DOM r=webgpu-reviewers,teoxoy

Differential Revision: https://phabricator.services.mozilla.com/D237088

gfx/wgpu_bindings/src/client.rs

@@ -10,6 +10,7 @@ use crate::{
 
 use crate::SwapChainId;
 
+use wgc::naga::front::wgsl::ImplementedLanguageExtension;
 use wgc::{command::RenderBundleEncoder, id, identity::IdentityManager};
 use wgt::{BufferAddress, BufferSize, DynamicOffset, IndexFormat, TextureFormat};
 
@@ -19,6 +20,7 @@ use parking_lot::Mutex;
 
 use nsstring::{nsACString, nsString};
 
+use std::fmt::Write;
 use std::{borrow::Cow, ptr};
 
 use self::render_pass::RenderPassDepthStencilAttachment;
@@ -419,6 +421,33 @@ pub extern "C" fn wgpu_client_fill_default_limits(limits: &mut wgt::Limits) {
     *limits = wgt::Limits::default();
 }
 
+/// Writes the single `WGSLLanguageFeature` associated with `index`, appending its identifier to the
+/// provided `buffer`. If `index` does not correspond to a valid feature index, then do nothing.
+///
+/// This function enables an FFI consumer to extract all implemented features in a loop, like so:
+///
+/// ```rust
+/// let mut buffer = nsstring::nsCString::new();
+/// for index in 0usize.. {
+///     buffer.truncate();
+///     wgpu_client_instance_get_wgsl_language_feature(&mut buffer, index);
+///     if buffer.is_empty() {
+///         break;
+///     }
+///     // Handle the identifier in `buffer`…
+/// }
+/// ```
+#[no_mangle]
+pub extern "C" fn wgpu_client_instance_get_wgsl_language_feature(
+    buffer: &mut nsstring::nsCString,
+    index: usize,
+) {
+    match ImplementedLanguageExtension::all().get(index) {
+        Some(some) => buffer.write_str(some.to_ident()).unwrap(),
+        None => (),
+    }
+}
+
 #[no_mangle]
 pub extern "C" fn wgpu_client_adapter_extract_info(
     byte_buf: &ByteBuf,