feat(wgsl): recognize enable primitive-index; (#8237)

Author: ErichDonGubler

CHANGELOG.md

@@ -166,6 +166,10 @@ By @cwfitzgerald in [#8162](https://github.com/gfx-rs/wgpu/pull/8162).
 
 - Added support for external textures based on WebGPU's [`GPUExternalTexture`](https://www.w3.org/TR/webgpu/#gpuexternaltexture). These allow shaders to transparently operate on potentially multiplanar source texture data in either RGB or YCbCr formats via WGSL's `texture_external` type. This is gated behind the `Features::EXTERNAL_TEXTURE` feature, which is currently only supported on DX12. By @jamienicol in [#4386](https://github.com/gfx-rs/wgpu/issues/4386).
 
+#### naga
+
+- Expose `naga::front::wgsl::UnimplementedEnableExtension`. By @ErichDonGubler in [#8237](https://github.com/gfx-rs/wgpu/pull/8237).
+
 ### Changes
 
 #### General

naga/src/front/wgsl/mod.rs

@@ -11,7 +11,9 @@ mod parse;
 #[cfg(test)]
 mod tests;
 
-pub use parse::directive::enable_extension::{EnableExtension, ImplementedEnableExtension};
+pub use parse::directive::enable_extension::{
+    EnableExtension, ImplementedEnableExtension, UnimplementedEnableExtension,
+};
 
 pub use crate::front::wgsl::error::ParseError;
 pub use crate::front::wgsl::parse::directive::language_extension::{

naga/src/front/wgsl/parse/directive/enable_extension.rs

@@ -71,6 +71,7 @@ impl EnableExtension {
     const CLIP_DISTANCES: &'static str = "clip_distances";
     const DUAL_SOURCE_BLENDING: &'static str = "dual_source_blending";
     const SUBGROUPS: &'static str = "subgroups";
+    const PRIMITIVE_INDEX: &'static str = "primitive_index";
 
     /// Convert from a sentinel word in WGSL into its associated [`EnableExtension`], if possible.
     pub(crate) fn from_ident(word: &str, span: Span) -> Result<'_, Self> {
@@ -81,6 +82,9 @@ impl EnableExtension {
                 Self::Implemented(ImplementedEnableExtension::DualSourceBlending)
             }
             Self::SUBGROUPS => Self::Unimplemented(UnimplementedEnableExtension::Subgroups),
+            Self::PRIMITIVE_INDEX => {
+                Self::Unimplemented(UnimplementedEnableExtension::PrimitiveIndex)
+            }
             _ => return Err(Box::new(Error::UnknownEnableExtension(span, word))),
         })
     }
@@ -95,6 +99,7 @@ impl EnableExtension {
             },
             Self::Unimplemented(kind) => match kind {
                 UnimplementedEnableExtension::Subgroups => Self::SUBGROUPS,
+                UnimplementedEnableExtension::PrimitiveIndex => Self::PRIMITIVE_INDEX,
             },
         }
     }
@@ -132,12 +137,19 @@ pub enum UnimplementedEnableExtension {
     ///
     /// [`enable subgroups;`]: https://www.w3.org/TR/WGSL/#extension-subgroups
     Subgroups,
+    /// Enables the `@builtin(primitive_index)` attribute in WGSL.
+    ///
+    /// In the WGSL standard, this corresponds to [`enable primitive-index;`].
+    ///
+    /// [`enable primitive-index;`]: https://www.w3.org/TR/WGSL/#extension-primitive_index
+    PrimitiveIndex,
 }
 
 impl UnimplementedEnableExtension {
     pub(crate) const fn tracking_issue_num(self) -> u16 {
         match self {
             Self::Subgroups => 5555,
+            Self::PrimitiveIndex => 8236,
         }
     }
 }

naga/tests/naga/wgsl_errors.rs

@@ -4098,6 +4098,46 @@ fn invalid_clip_distances() {
     }
 }
 
+#[test]
+fn recognized_but_unimplemented_enable_extension() {
+    for extension in [
+        naga::front::wgsl::UnimplementedEnableExtension::Subgroups,
+        naga::front::wgsl::UnimplementedEnableExtension::PrimitiveIndex,
+    ] {
+        // NOTE: We match exhaustively here to help maintainers add or remove variants to the above
+        // array.
+        let snapshot = match extension {
+            naga::front::wgsl::UnimplementedEnableExtension::Subgroups => "\
+error: the `subgroups` enable-extension is not yet supported
+  ┌─ wgsl:1:8
+  │
+1 │ enable subgroups;
+  │        ^^^^^^^^^ this enable-extension specifies standard functionality which is not yet implemented in Naga
+  │
+  = note: Let Naga maintainers know that you ran into this at <https://github.com/gfx-rs/wgpu/issues/5555>, so they can prioritize it!
+
+",
+            naga::front::wgsl::UnimplementedEnableExtension::PrimitiveIndex => "\
+error: the `primitive_index` enable-extension is not yet supported
+  ┌─ wgsl:1:8
+  │
+1 │ enable primitive_index;
+  │        ^^^^^^^^^^^^^^^ this enable-extension specifies standard functionality which is not yet implemented in Naga
+  │
+  = note: Let Naga maintainers know that you ran into this at <https://github.com/gfx-rs/wgpu/issues/8236>, so they can prioritize it!
+
+",
+        };
+
+        let shader = {
+            let extension = naga::front::wgsl::EnableExtension::Unimplemented(extension);
+            format!("enable {};", extension.to_ident())
+        };
+
+        check(&shader, snapshot);
+    }
+}
+
 #[test]
 fn max_type_size_large_array() {
     // The total size of an array is not resolved until validation. Type aliases