add parse (!) error for enable feature flag

Author: Wumpf

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

@@ -25,7 +25,6 @@ impl EnableExtensions {
     }
 
     /// Query whether an enable-extension tracked here has been requested.
-    #[allow(unused)]
     pub(crate) const fn contains(&self, ext: ImplementedEnableExtension) -> bool {
         match ext {
             ImplementedEnableExtension::DualSourceBlending => self.dual_source_blending,
@@ -49,6 +48,12 @@ pub enum EnableExtension {
     Unimplemented(UnimplementedEnableExtension),
 }
 
+impl From<ImplementedEnableExtension> for EnableExtension {
+    fn from(value: ImplementedEnableExtension) -> Self {
+        Self::Implemented(value)
+    }
+}
+
 impl EnableExtension {
     const F16: &'static str = "f16";
     const CLIP_DISTANCES: &'static str = "clip_distances";

naga/src/front/wgsl/parse/lexer.rs

@@ -218,7 +218,6 @@ pub(in crate::front::wgsl) struct Lexer<'a> {
     /// statements.
     last_end_offset: usize,
 
-    #[allow(dead_code)]
     pub(in crate::front::wgsl) enable_extensions: EnableExtensions,
 }
 

naga/src/front/wgsl/parse/mod.rs

@@ -1,3 +1,5 @@
+use directive::enable_extension::ImplementedEnableExtension;
+
 use crate::diagnostic_filter::{
     self, DiagnosticFilter, DiagnosticFilterMap, DiagnosticFilterNode, FilterableTriggeringRule,
     ShouldConflictOnFullDuplicate, StandardFilterableTriggeringRule,
@@ -221,6 +223,16 @@ impl<'a> BindingParser<'a> {
                 self.invariant.set(true, name_span)?;
             }
             "blend_src" => {
+                if !lexer
+                    .enable_extensions
+                    .contains(ImplementedEnableExtension::DualSourceBlending)
+                {
+                    return Err(Error::EnableExtensionNotEnabled {
+                        span: name_span,
+                        kind: ImplementedEnableExtension::DualSourceBlending.into(),
+                    });
+                }
+
                 lexer.expect(Token::Paren('('))?;
                 self.blend_src
                     .set(parser.general_expression(lexer, ctx)?, name_span)?;

naga/src/valid/interface.rs

@@ -319,7 +319,6 @@ impl VaryingContext<'_> {
                 if let Some(blend_src) = blend_src {
                     // `blend_src` is only valid if dual source blending was explicitly enabled,
                     // see https://www.w3.org/TR/WGSL/#extension-dual_source_blending
-                    // TODO: check that dual source blending feature was enabled in the shader.
                     if !self
                         .capabilities
                         .contains(Capabilities::DUAL_SOURCE_BLENDING)

naga/tests/wgsl_errors.rs

@@ -1345,19 +1345,23 @@ fn invalid_blend_src() {
     }
 
     // Missing enable directive.
-    // TODO:
-    // check_validation! {
-    //     "
-    //     struct FragmentOutput {
-    //         @location(0) @blend_src(0) output0: vec4<f32>,
-    //         @location(0) @blend_src(1) output1: vec4<f32>,
-    //     }
-    //     @fragment
-    //     fn main(@builtin(position) position: vec4<f32>) -> FragmentOutput { return FragmentOutput(vec4(0.0), vec4(0.0)); }
-    //     ":
-    //     Err(???),
-    //     Capabilities::DUAL_SOURCE_BLENDING
-    // }
+    // Note that this is a parsing error, not a validation error.
+    check("
+        struct FragmentOutput {
+            @location(0) @blend_src(0) output0: vec4<f32>,
+            @location(0) @blend_src(1) output1: vec4<f32>,
+        }
+        @fragment
+        fn main(@builtin(position) position: vec4<f32>) -> FragmentOutput { return FragmentOutput(vec4(0.0), vec4(0.0)); }
+        ",
+        r###"error: `dual_source_blending` enable-extension is not enabled
+  ┌─ wgsl:3:27
+  │
+3 │             @location(0) @blend_src(0) output0: vec4<f32>,
+  │                           ^^^^^^^^^ the `dual_source_blending` enable-extension is needed for this functionality, but it is not currently enabled
+
+"###,
+    );
 
     // Using blend_src on an input.
     check_validation! {