Made u128 -> u64 conversion clearer

chia-protocol/src/vdf.rs

@@ -6,7 +6,7 @@ use crate::{Bytes, Bytes32};
 
 streamable_struct!(VDFInfo {
     challenge: Bytes32,
-    number_of_iterations: u64,
+    number_of_iterations: u128,
     output: ClassgroupElement,
 });
 

wasm-patch/Cargo.toml

@@ -11,4 +11,4 @@ proc-macro = true
 [dependencies]
 proc-macro2 = "1.0.70"
 quote = "1.0.33"
-syn = "2.0.39"
+syn = { version = "2.0.39", features = ["full", "visit-mut"]}

wasm-patch/src/lib.rs

@@ -1,33 +1,39 @@
 extern crate proc_macro;
 
+use syn::{visit_mut::VisitMut, parse_quote, Type};
 use proc_macro::{TokenStream};
-use syn::{Item, parse_macro_input};
 
-fn attach_wasm_bindgen(input: &TokenStream) -> TokenStream {
-    let mut t = input.to_string();
-    t = format!("#[wasm_bindgen::prelude::wasm_bindgen(getter_with_clone)] {}", t);
-    t.parse().unwrap()
+// See https://github.com/rustwasm/wasm-bindgen/issues/3707
+fn _patch_issue_3707(input: &TokenStream) -> TokenStream {
+    let mut s = input.to_string();
+    s = format!("#[wasm_bindgen::prelude::wasm_bindgen(getter_with_clone)] {}", s);
+    s.parse().unwrap()
 }
 
-#[proc_macro_attribute]
-pub fn with_wasm(_args: TokenStream, input: TokenStream) -> TokenStream {
-    let mut input_maybe_modified = input.clone();
+struct TypeConverter;
 
-    let parsed_item = parse_macro_input!(input as Item);
-
-    match parsed_item {
-        Item::Struct(_) => {
-            let shrink_u128 = true;
-            if shrink_u128 {
-                let mut s = input_maybe_modified.to_string();
-                s = s.replace("u128", "u64");
-                input_maybe_modified = s.parse().unwrap();
+// As of Dec 2023, wasm-bindgen cannot handle u128 at all.
+// We convert u128 into u64 here.
+// u64 is then converted into bigint in JS which has no size limitation.
+// So this conversion does no harm unless a value greater than u64_max is
+// communicated between JS and Wasm Runtime.
+impl VisitMut for TypeConverter {
+    fn visit_type_mut(&mut self, i: &mut Type) {
+        if let Type::Path(type_path) = i {
+            if type_path.path.is_ident("u128") {
+                *i = parse_quote! { u64 };
             }
-            // println!("{}", &input_maybe_modified);
-            attach_wasm_bindgen(&input_maybe_modified)
-        },
-        _ => {
-            attach_wasm_bindgen(&input_maybe_modified)
         }
+        syn::visit_mut::visit_type_mut(self, i);
     }
 }
+
+#[proc_macro_attribute]
+pub fn with_wasm(_args: TokenStream, input: TokenStream) -> TokenStream {
+    let mut ast: syn::File = syn::parse(input.into()).unwrap();
+    let mut converter = TypeConverter;
+    converter.visit_file_mut(&mut ast);
+
+    let input_maybe_modified = quote::quote!(#ast);
+    _patch_issue_3707(&input_maybe_modified.into())
+}