[naga] implement pointer_composite_access WGSL language extension (#…

…6913)

Co-authored-by: Erich Gubler <[email protected]>

CHANGELOG.md

@@ -270,6 +270,7 @@ By @ErichDonGubler in [#6456](https://github.com/gfx-rs/wgpu/pull/6456), [#6148]
 - Add support for OpAtomicCompareExchange in SPIR-V frontend. By @schell in [#6590](https://github.com/gfx-rs/wgpu/pull/6590).
 - Implement type inference for abstract arguments to user-defined functions. By @jamienicol in [#6577](https://github.com/gfx-rs/wgpu/pull/6577).
 - Allow for override-expressions in array sizes. By @KentSlaney in [#6654](https://github.com/gfx-rs/wgpu/pull/6654).
+- [`pointer_composite_access` WGSL language extension](https://www.w3.org/TR/WGSL/#language_extension-pointer_composite_access) is implemented. By @sagudev in [#6913](https://github.com/gfx-rs/wgpu/pull/6913)
 
 ##### General
 

naga/src/front/wgsl/error.rs

@@ -213,7 +213,6 @@ pub(crate) enum Error<'a> {
     InvalidAtomicPointer(Span),
     InvalidAtomicOperandType(Span),
     InvalidRayQueryPointer(Span),
-    Pointer(&'static str, Span),
     NotPointer(Span),
     NotReference(&'static str, Span),
     InvalidAssignment {
@@ -719,11 +718,6 @@ impl<'a> Error<'a> {
                     notes,
                 }
             }
-            Error::Pointer(what, span) => ParseError {
-                message: format!("{what} must not be a pointer"),
-                labels: vec![(span, "expression is a pointer".into())],
-                notes: vec![],
-            },
             Error::ReservedKeyword(name_span) => ParseError {
                 message: format!("name `{}` is a reserved keyword", &source[name_span]),
                 labels: vec![(

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

@@ -1998,15 +1998,14 @@ impl<'source, 'temp> Lowerer<'source, 'temp> {
                 return Ok(Typed::Plain(handle));
             }
             ast::Expression::Index { base, index } => {
-                let lowered_base = self.expression_for_reference(base, ctx)?;
+                let mut lowered_base = self.expression_for_reference(base, ctx)?;
                 let index = self.expression(index, ctx)?;
 
+                // <https://www.w3.org/TR/WGSL/#language_extension-pointer_composite_access>
+                // Declare pointer as reference
                 if let Typed::Plain(handle) = lowered_base {
                     if resolve_inner!(ctx, handle).pointer_space().is_some() {
-                        return Err(Error::Pointer(
-                            "the value indexed by a `[]` subscripting expression",
-                            ctx.ast_expressions.get_span(base),
-                        ));
+                        lowered_base = Typed::Reference(handle);
                     }
                 }
 
@@ -2016,7 +2015,15 @@ impl<'source, 'temp> Lowerer<'source, 'temp> {
                 })
             }
             ast::Expression::Member { base, ref field } => {
-                let lowered_base = self.expression_for_reference(base, ctx)?;
+                let mut lowered_base = self.expression_for_reference(base, ctx)?;
+
+                // <https://www.w3.org/TR/WGSL/#language_extension-pointer_composite_access>
+                // Declare pointer as reference
+                if let Typed::Plain(handle) = lowered_base {
+                    if resolve_inner!(ctx, handle).pointer_space().is_some() {
+                        lowered_base = Typed::Reference(handle);
+                    }
+                }
 
                 let temp_inner;
                 let composite_type: &crate::TypeInner = match lowered_base {
@@ -2045,16 +2052,7 @@ impl<'source, 'temp> Lowerer<'source, 'temp> {
                     }
 
                     Typed::Plain(handle) => {
-                        let inner = resolve_inner!(ctx, handle);
-                        if let crate::TypeInner::Pointer { .. }
-                        | crate::TypeInner::ValuePointer { .. } = *inner
-                        {
-                            return Err(Error::Pointer(
-                                "the value accessed by a `.member` expression",
-                                ctx.ast_expressions.get_span(base),
-                            ));
-                        }
-                        inner
+                        resolve_inner!(ctx, handle)
                     }
                 };
 

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

@@ -34,7 +34,7 @@ impl LanguageExtension {
                 Self::Unimplemented(UnimplementedLanguageExtension::UnrestrictedPointerParameters)
             }
             Self::POINTER_COMPOSITE_ACCESS => {
-                Self::Unimplemented(UnimplementedLanguageExtension::PointerCompositeAccess)
+                Self::Implemented(ImplementedLanguageExtension::PointerCompositeAccess)
             }
             _ => return None,
         })
@@ -54,17 +54,16 @@ impl LanguageExtension {
                 UnimplementedLanguageExtension::UnrestrictedPointerParameters => {
                     Self::UNRESTRICTED_POINTER_PARAMETERS
                 }
-                UnimplementedLanguageExtension::PointerCompositeAccess => {
-                    Self::POINTER_COMPOSITE_ACCESS
-                }
             },
         }
     }
 }
 
 /// A variant of [`LanguageExtension::Implemented`].
 #[derive(Clone, Copy, Debug, Eq, Hash, PartialEq, VariantArray)]
-pub enum ImplementedLanguageExtension {}
+pub enum ImplementedLanguageExtension {
+    PointerCompositeAccess,
+}
 
 impl ImplementedLanguageExtension {
     /// Returns slice of all variants of [`ImplementedLanguageExtension`].
@@ -74,7 +73,11 @@ impl ImplementedLanguageExtension {
 
     /// Maps this [`ImplementedLanguageExtension`] into the sentinel word associated with it in WGSL.
     pub const fn to_ident(self) -> &'static str {
-        match self {}
+        match self {
+            ImplementedLanguageExtension::PointerCompositeAccess => {
+                LanguageExtension::POINTER_COMPOSITE_ACCESS
+            }
+        }
     }
 }
 
@@ -84,7 +87,6 @@ pub enum UnimplementedLanguageExtension {
     ReadOnlyAndReadWriteStorageTextures,
     Packed4x8IntegerDotProduct,
     UnrestrictedPointerParameters,
-    PointerCompositeAccess,
 }
 
 impl UnimplementedLanguageExtension {
@@ -93,7 +95,6 @@ impl UnimplementedLanguageExtension {
             Self::ReadOnlyAndReadWriteStorageTextures => 6204,
             Self::Packed4x8IntegerDotProduct => 6445,
             Self::UnrestrictedPointerParameters => 5158,
-            Self::PointerCompositeAccess => 6192,
         }
     }
 }

naga/tests/in/access.wgsl

@@ -198,3 +198,47 @@ fn assign_to_ptr_components() {
    assign_to_arg_ptr_array_element(&a1);
    fetch_arg_ptr_array_element(&a1);
 }
+
+fn index_ptr(value: bool) -> bool {
+    var a = array<bool, 1>(value);
+    let p = &a;
+    return p[0];
+}
+
+struct S { m: i32 };
+
+fn member_ptr() -> i32 {
+    var s: S = S(42);
+    let p = &s;
+    return p.m;
+}
+
+struct Inner { delicious: i32 }
+
+struct Outer { om_nom_nom: Inner, thing: u32 }
+
+fn let_members_of_members() -> i32 {
+    let thing = Outer();
+
+    let inner = thing.om_nom_nom;
+    let delishus = inner.delicious;
+
+    if (thing.thing != u32(delishus)) {
+        // LOL
+    }
+
+    return thing.om_nom_nom.delicious;
+}
+
+fn var_members_of_members() -> i32 {
+    var thing = Outer();
+
+    var inner = thing.om_nom_nom;
+    var delishus = inner.delicious;
+
+    if (thing.thing != u32(delishus)) {
+        // LOL
+    }
+
+    return thing.om_nom_nom.delicious;
+}