implement GuestType for arrays

crates/wiggle/src/guest_type.rs

@@ -153,3 +153,30 @@ impl<'a, T> GuestType<'a> for GuestPtr<'a, T> {
         ptr.cast::<u32>().write(val.offset())
     }
 }
+
+// Support pointers-to-arrays where pointers are always 32-bits in wasm land
+impl<'a, T> GuestType<'a> for GuestPtr<'a, [T]>
+where
+    T: GuestType<'a>,
+{
+    fn guest_size() -> u32 {
+        u32::guest_size() * 2
+    }
+
+    fn guest_align() -> usize {
+        u32::guest_align()
+    }
+
+    fn read(ptr: &GuestPtr<'a, Self>) -> Result<Self, GuestError> {
+        let offset = ptr.cast::<u32>().read()?;
+        let len = ptr.cast::<u32>().add(1)?.read()?;
+        Ok(GuestPtr::new(ptr.mem(), offset).as_array(len))
+    }
+
+    fn write(ptr: &GuestPtr<'_, Self>, val: Self) -> Result<(), GuestError> {
+        let (offs, len) = val.offset();
+        let len_ptr = ptr.cast::<u32>().add(1)?;
+        ptr.cast::<u32>().write(offs)?;
+        len_ptr.write(len)
+    }
+}