fix(wgsl): narrow accepted args. of cross to vec3<$float>

CHANGELOG.md

@@ -79,6 +79,10 @@ By @teoxoy [#6134](https://github.com/gfx-rs/wgpu/pull/6134).
 
 - Fix incorrect hlsl image output type conversion. By @atlv24 in [#6123](https://github.com/gfx-rs/wgpu/pull/6123)
 
+#### Naga
+
+- Accept only `vec3` (not `vecN`) for the `cross` built-in. By @ErichDonGubler in [#6171](https://github.com/gfx-rs/wgpu/pull/6171).
+
 #### General
 
 - If GL context creation fails retry with GLES. By @Rapdorian in [#5996](https://github.com/gfx-rs/wgpu/pull/5996)

naga/src/valid/expression.rs

@@ -1172,8 +1172,8 @@ impl super::Validator {
                                     Sc {
                                         kind: Sk::Float, ..
                                     },
-                                ..
+                                size: vector_size,
-                            } => {}
+                            } if fun != Mf::Cross || vector_size == crate::VectorSize::Tri => {}
                             _ => return Err(ExpressionError::InvalidArgumentType(fun, 0, arg)),
                         }
                         if arg1_ty != arg_ty {

naga/tests/validation.rs

@@ -260,3 +260,54 @@ fn emit_workgroup_uniform_load_result() {
     variant(true).expect("module should validate");
     assert!(variant(false).is_err());
 }
+
+#[cfg(feature = "wgsl-in")]
+#[test]
+fn bad_cross_builtin_args() {
+    let cases = [
+        (
+            "vec2(0., 1.)",
+            "\
+error: Entry point main at Compute is invalid
+  ┌─ wgsl:3:13
+  │
+3 │     let a = cross(vec2(0., 1.), vec2(0., 1.));
+  │             ^^^^^ naga::Expression [6]
+  │
+  = Expression [6] is invalid
+  = Argument [0] to Cross as expression [2] has an invalid type.
+
+",
+        ),
+        (
+            "vec4(0., 1., 2., 3.)",
+            "\
+error: Entry point main at Compute is invalid
+  ┌─ wgsl:3:13
+  │
+3 │     let a = cross(vec4(0., 1., 2., 3.), vec4(0., 1., 2., 3.));
+  │             ^^^^^ naga::Expression [10]
+  │
+  = Expression [10] is invalid
+  = Argument [0] to Cross as expression [4] has an invalid type.
+
+",
+        ),
+    ];
+
+    for (invalid_arg, expected_err) in cases {
+        let source = format!(
+            "\
+@compute @workgroup_size(1)
+fn main() {{
+    let a = cross({invalid_arg}, {invalid_arg});
+}}
+"
+        );
+        let module = naga::front::wgsl::parse_str(&source).unwrap();
+        let err = valid::Validator::new(Default::default(), valid::Capabilities::all())
+            .validate_no_overrides(&module)
+            .expect_err("module should be invalid");
+        assert_eq!(err.emit_to_string(&source), expected_err);
+    }
+}