Add support for constructing JsValue instances generically

crates/backend/src/codegen.rs

@@ -88,6 +88,7 @@ impl ToTokens for ast::Program {
 impl ToTokens for ast::Struct {
     fn to_tokens(&self, tokens: &mut Tokens) {
         let name = &self.name;
+        let new_fn = syn::Ident::from(shared::new_function(self.name.as_ref()));
         let free_fn = syn::Ident::from(shared::free_function(self.name.as_ref()));
         let c = shared::name_to_descriptor(name.as_ref());
         let descriptor = Literal::byte_string(format!("{:4}", c).as_bytes());
@@ -153,6 +154,21 @@ impl ToTokens for ast::Struct {
                 }
             }
 
+            impl ::std::convert::From<#name> for ::wasm_bindgen::JsValue {
+                fn from(value: #name) -> Self {
+                    let ptr = ::wasm_bindgen::convert::WasmBoundary::into_js(value);
+
+                    #[wasm_import_module = "__wbindgen_placeholder__"]
+                    extern {
+                        fn #new_fn(ptr: u32) -> u32;
+                    }
+
+                    unsafe {
+                        ::wasm_bindgen::JsValue::__from_idx(#new_fn(ptr))
+                    }
+                }
+            }
+
             #[no_mangle]
             pub unsafe extern fn #free_fn(ptr: u32) {
                 <#name as ::wasm_bindgen::convert::WasmBoundary>::from_abi(

crates/cli-support/src/js.rs

@@ -266,6 +266,11 @@ impl<'a> Context<'a> {
                     }}
                 "));
                 ts_dst.push_str("constructor(ptr: number, sym: Symbol);\n");
+
+                self.globals.push_str(&format!("
+                    export function {new_name}(ptr) {{
+                        return addHeapObject(new {class}(ptr, token));
+                    }}", new_name=shared::new_function(&class), class=class));
             } else {
                 dst.push_str(&format!("
                     constructor(ptr) {{
@@ -273,6 +278,11 @@ impl<'a> Context<'a> {
                     }}
                 "));
                 ts_dst.push_str("constructor(ptr: number);\n");
+
+                self.globals.push_str(&format!("
+                    export function {new_name}(ptr) {{
+                        return addHeapObject(new {class}(ptr));
+                    }}", new_name=shared::new_function(&class), class=class));
             }
 
             dst.push_str(&format!("

crates/shared/src/lib.rs

@@ -88,6 +88,15 @@ pub struct CustomTypeName {
     pub name: String,
 }
 
+pub fn new_function(struct_name: &str) -> String {
+    let mut name = format!("__wbg_");
+    name.extend(struct_name
+        .chars()
+        .flat_map(|s| s.to_lowercase()));
+    name.push_str("_new");
+    return name
+}
+
 pub fn free_function(struct_name: &str) -> String {
     let mut name = format!("__wbg_");
     name.extend(struct_name