[naga] Have validation reject shaders containing binding arrays of external textures

For simplicity's sake our initial implementation of external textures
will not support binding arrays of external textures. We should
therefore reject any shaders which use them during validation.

Their implementation will be tracked in #8027.

naga/src/valid/type.rs JJ: JJ: Lines starting with "JJ:" (like this
one) will be removed.

Author: jamienicol

naga/src/valid/type.rs

@@ -133,6 +133,8 @@ pub enum TypeError {
     InvalidDynamicArray(String, Handle<crate::Type>),
     #[error("The base handle {0:?} has to be a struct")]
     BindingArrayBaseTypeNotStruct(Handle<crate::Type>),
+    #[error("Binding arrays of external textures are not yet supported")]
+    BindingArrayBaseExternalTextures,
     #[error("Structure member[{index}] at {offset} overlaps the previous member")]
     MemberOverlap { index: u32, offset: u32 },
     #[error(
@@ -803,6 +805,17 @@ impl super::Validator {
                         _ => return Err(TypeError::BindingArrayBaseTypeNotStruct(base)),
                     };
                 }
+                if matches!(
+                    gctx.types[base].inner,
+                    crate::TypeInner::Image {
+                        class: crate::ImageClass::External,
+                        ..
+                    }
+                ) {
+                    // Binding arrays of external textures are not yet supported.
+                    // https://github.com/gfx-rs/wgpu/issues/8027
+                    return Err(TypeError::BindingArrayBaseExternalTextures);
+                }
 
                 if !base_info.flags.contains(TypeFlags::CREATION_RESOLVED) {
                     return Err(TypeError::InvalidData(base));