Rust: Add validation support to code generator

mojom/generators/rust/rustgen/type_translation.go

Index: mojom/generators/rust/rustgen/type_translation.go
diff --git a/mojom/generators/rust/rustgen/type_translation.go b/mojom/generators/rust/rustgen/type_translation.go
index b08d1250efd4fa20c5a10a409c6ac9ac64ff9f4d..1bbc3fb6f0b6c4808786f6923c060e7bf58dacec 100644
--- a/mojom/generators/rust/rustgen/type_translation.go
+++ b/mojom/generators/rust/rustgen/type_translation.go
@@ -232,8 +232,14 @@ func mojomToRustType(t mojom_types.Type, context *Context) string {
 			len_str := strconv.Itoa(int(array_type.FixedLength))
 			type_str = "[" + elem_type_str + "; " + len_str + "]"
 		} else {
+			log.Fatal("Rust doesn't currently support arrays of " +
+				  "fixed size greater than 32. The reason for this is " +
+				  "the lack of generics over array length in the type " +
+				  "system. Since we cannot encode the length in the type " +
+				  "there is no way for nested decode routines to know " +
+				  "what length it should be. Sorry. :(")
 			// Fixed length array, but user has to validate the length themselves.
-			type_str = "Box<[" + elem_type_str + "]>"
+			//type_str = "Box<[" + elem_type_str + "]>"
 		}
 		if array_type.Nullable {
 			return "Option<" + type_str + ">"