Classes are now working!

Cargo.toml

@@ -8,3 +8,6 @@ wasm-bindgen-macro = { path = "crates/wasm-bindgen-macro" }
 
 [dev-dependencies]
 test-support = { path = "crates/test-support" }
+
+[workspace]
+members = ["crates/wasm-bindgen-cli"]

crates/test-support/src/lib.rs

@@ -9,6 +9,9 @@ use std::sync::atomic::*;
 use std::sync::{Once, ONCE_INIT};
 use std::time::Instant;
 
+static CNT: AtomicUsize = ATOMIC_USIZE_INIT;
+thread_local!(static IDX: usize = CNT.fetch_add(1, Ordering::SeqCst));
+
 pub struct Project {
     files: Vec<(String, String)>,
 }
@@ -25,10 +28,12 @@ pub fn project() -> Project {
         files: vec![
             ("Cargo.toml".to_string(), format!(r#"
                 [package]
-                name = "test"
+                name = "test{}"
                 version = "0.0.1"
                 authors = []
 
+                [workspace]
+
                 [lib]
                 crate-type = ["cdylib"]
 
@@ -37,7 +42,7 @@ pub fn project() -> Project {
 
                 [profile.dev]
                 opt-level = 2 # TODO: decrease when upstream is not buggy
-            "#, dir.display())),
+            "#, IDX.with(|x| *x), dir.display())),
 
             ("Cargo.lock".to_string(), lockfile),
 
@@ -60,8 +65,6 @@ pub fn project() -> Project {
 }
 
 pub fn root() -> PathBuf {
-    static CNT: AtomicUsize = ATOMIC_USIZE_INIT;
-    thread_local!(static IDX: usize = CNT.fetch_add(1, Ordering::SeqCst));
     let idx = IDX.with(|x| *x);
 
     let mut me = env::current_exe().unwrap();
@@ -123,7 +126,8 @@ impl Project {
             .env("CARGO_TARGET_DIR", &target_dir);
         run(&mut cmd, "cargo");
 
-        let mut out = target_dir.join("wasm32-unknown-unknown/debug/test.wasm");
+        let idx = IDX.with(|x| *x);
+        let mut out = target_dir.join(&format!("wasm32-unknown-unknown/debug/test{}.wasm", idx));
         if Command::new("wasm-gc").output().is_ok() {
             let tmp = out;
             out = tmp.with_extension("gc.wasm");

crates/wasm-bindgen-cli-support/src/js.rs

@@ -4,7 +4,11 @@ use shared;
 pub struct Js {
     pub expose_global_memory: bool,
     pub expose_global_exports: bool,
+    pub expose_get_string_from_wasm: bool,
+    pub expose_pass_string_to_wasm: bool,
+    pub expose_token: bool,
     pub exports: Vec<(String, String)>,
+    pub classes: Vec<String>,
     pub nodejs: bool,
 }
 
@@ -14,6 +18,9 @@ impl Js {
         for f in program.free_functions.iter() {
             self.generate_free_function(f);
         }
+        for s in program.structs.iter() {
+            self.generate_struct(s);
+        }
     }
 
     pub fn generate_free_function(&mut self, func: &shared::Function) {
@@ -28,12 +35,76 @@ impl Js {
             return
         }
 
-        let mut dst = format!("function {}(", func.name);
+        let ret = self.generate_function(&format!("function {}", func.name),
+                                         &func.name,
+                                         false,
+                                         &func.arguments,
+                                         func.ret.as_ref());
+
+        self.exports.push((func.name.clone(), ret));
+    }
+
+    pub fn generate_struct(&mut self, s: &shared::Struct) {
+        let mut dst = String::new();
+        self.expose_token = true;
+        self.expose_global_exports = true;
+        dst.push_str(&format!("
+            class {} {{
+                constructor(ptr, sym) {{
+                    _checkToken(sym);
+                    this.__wasmPtr = ptr;
+                }}
+
+                free() {{
+                    const ptr = this.__wasmPtr;
+                    this.__wasmPtr = 0;
+                    exports.{}(ptr);
+                }}
+        ", s.name, s.free_function()));
+
+        for function in s.functions.iter() {
+            let f = self.generate_function(
+                &format!("static {}", function.name),
+                &function.struct_function_export_name(&s.name),
+                false,
+                &function.arguments,
+                function.ret.as_ref(),
+            );
+            dst.push_str(&f);
+            dst.push_str("\n");
+        }
+        for method in s.methods.iter() {
+            let f = self.generate_function(
+                &format!("{}", method.function.name),
+                &method.function.struct_function_export_name(&s.name),
+                true,
+                &method.function.arguments,
+                method.function.ret.as_ref(),
+            );
+            dst.push_str(&f);
+            dst.push_str("\n");
+        }
+        dst.push_str("}\n");
+        self.classes.push(dst);
+        self.exports.push((s.name.clone(), s.name.clone()));
+    }
+
+    fn generate_function(&mut self,
+                         name: &str,
+                         wasm_name: &str,
+                         is_method: bool,
+                         arguments: &[shared::Type],
+                         ret: Option<&shared::Type>) -> String {
+        let mut dst = format!("{}(", name);
         let mut passed_args = String::new();
         let mut arg_conversions = String::new();
         let mut destructors = String::new();
 
-        for (i, arg) in func.arguments.iter().enumerate() {
+        if is_method {
+            passed_args.push_str("this.__wasmPtr");
+        }
+
+        for (i, arg) in arguments.iter().enumerate() {
             let name = format!("arg{}", i);
             if i > 0 {
                 dst.push_str(", ");
@@ -50,23 +121,17 @@ impl Js {
                 shared::Type::Number => pass(&name),
                 shared::Type::BorrowedStr |
                 shared::Type::String => {
-                    if self.nodejs {
-                        arg_conversions.push_str(&format!("\
-                            const buf{i} = Buffer.from({arg});
-                            const len{i} = buf{i}.length;
-                            const ptr{i} = exports.__wbindgen_malloc(len{i});
-                            let memory{i} = new Uint8Array(memory.buffer);
-                            buf{i}.copy(memory{i}, ptr{i});
-                        ", i = i, arg = name));
-                        pass(&format!("ptr{}", i));
-                        pass(&format!("len{}", i));
-                        if let shared::Type::BorrowedStr = *arg {
-                            destructors.push_str(&format!("\n\
-                                exports.__wbindgen_free(ptr{i}, len{i});\n\
-                            ", i = i));
-                        }
-                    } else {
-                        panic!("strings not implemented for browser");
+                    self.expose_global_exports = true;
+                    self.expose_pass_string_to_wasm = true;
+                    arg_conversions.push_str(&format!("\
+                        const [ptr{i}, len{i}] = passStringToWasm({arg});
+                    ", i = i, arg = name));
+                    pass(&format!("ptr{}", i));
+                    pass(&format!("len{}", i));
+                    if let shared::Type::BorrowedStr = *arg {
+                        destructors.push_str(&format!("\n\
+                            exports.__wbindgen_free(ptr{i}, len{i});\n\
+                        ", i = i));
                     }
                 }
                 shared::Type::ByRef(_) |
@@ -85,59 +150,107 @@ impl Js {
                 }
             }
         }
-        let convert_ret = match func.ret {
+        let convert_ret = match ret {
             None |
-            Some(shared::Type::Number) => format!("return ret;"),
-            Some(shared::Type::BorrowedStr) |
-            Some(shared::Type::ByMutRef(_)) |
-            Some(shared::Type::ByRef(_)) => panic!(),
-            Some(shared::Type::ByValue(ref name)) => {
+            Some(&shared::Type::Number) => format!("return ret;"),
+            Some(&shared::Type::BorrowedStr) |
+            Some(&shared::Type::ByMutRef(_)) |
+            Some(&shared::Type::ByRef(_)) => panic!(),
+            Some(&shared::Type::ByValue(ref name)) => {
                 format!("\
-                    return {name}.__wasmWrap(ret);
+                    return new {name}(ret, token);
                 ", name = name)
             }
-            Some(shared::Type::String) => {
-                if self.nodejs {
-                    format!("\
-                        const mem = new Uint8Array(memory.buffer);
-                        const ptr = exports.__wbindgen_boxed_str_ptr(ret);
-                        const len = exports.__wbindgen_boxed_str_len(ret);
-                        const buf = Buffer.from(mem.slice(ptr, ptr + len));
-                        const realRet = buf.toString();
-                        exports.__wbindgen_boxed_str_free(ret);
-                        return realRet;
-                    ")
-                } else {
-                    panic!("strings not implemented for browser");
-                }
+            Some(&shared::Type::String) => {
+                self.expose_get_string_from_wasm = true;
+                format!("return getStringFromWasm(ret);")
             }
         };
         dst.push_str(") {\n        ");
         dst.push_str(&arg_conversions);
-        dst.push_str(&format!("\
-            try {{
+        self.expose_global_exports = true;
+        if destructors.len() == 0 {
+            dst.push_str(&format!("\
                 const ret = exports.{f}({passed});
                 {convert_ret}
-            }} finally {{
-                {destructors}
-            }}
-        ", f = func.name, passed = passed_args, destructors = destructors,
-            convert_ret = convert_ret));
-        dst.push_str("};");
-
-        self.exports.push((func.name.clone(), dst));
+            ", f = wasm_name, passed = passed_args, convert_ret = convert_ret));
+        } else {
+            dst.push_str(&format!("\
+                try {{
+                    const ret = exports.{f}({passed});
+                    {convert_ret}
+                }} finally {{
+                    {destructors}
+                }}
+            ", f = wasm_name, passed = passed_args, destructors = destructors,
+                convert_ret = convert_ret));
+        }
+        dst.push_str("}");
+        return dst
     }
 
     pub fn to_string(&self) -> String {
         let mut globals = String::new();
-        if self.expose_global_memory {
+        if self.expose_global_memory ||
+            self.expose_pass_string_to_wasm ||
+            self.expose_get_string_from_wasm
+        {
             globals.push_str("const memory = obj.instance.exports.memory;\n");
         }
-        if self.expose_global_exports {
+        if self.expose_global_exports ||
+            self.expose_pass_string_to_wasm ||
+            self.expose_get_string_from_wasm
+        {
             globals.push_str("const exports = obj.instance.exports;\n");
         }
+        if self.expose_token {
+            globals.push_str("\
+                const token = Symbol('foo');
+                function _checkToken(sym) {
+                    if (token != sym)
+                        throw new Error('cannot invoke `new` directly');
+                }
+            ");
+        }
+        if self.expose_pass_string_to_wasm {
+            if self.nodejs {
+                globals.push_str("
+                    function passStringToWasm(arg) {
+                        const buf = Buffer.from(arg);
+                        const len = buf.length;
+                        const ptr = exports.__wbindgen_malloc(len);
+                        let array = new Uint8Array(memory.buffer);
+                        buf.copy(array, ptr);
+                        return [ptr, len];
+                    }
+                ");
+            } else {
+                panic!("browser strings not implemented yet");
+            }
+        }
+        if self.expose_get_string_from_wasm {
+            if self.nodejs {
+                globals.push_str("
+                    function getStringFromWasm(ptr) {
+                        const mem = new Uint8Array(memory.buffer);
+                        const data = exports.__wbindgen_boxed_str_ptr(ptr);
+                        const len = exports.__wbindgen_boxed_str_len(ptr);
+                        const buf = Buffer.from(mem.slice(data, data + len));
+                        const ret = buf.toString();
+                        exports.__wbindgen_boxed_str_free(ptr);
+                        return ret;
+                    }
+                ");
+            } else {
+                panic!("strings not implemented for browser");
+            }
+        }
 
         let mut exports = String::new();
+        for class in self.classes.iter() {
+            exports.push_str(class);
+            exports.push_str("\n");
+        }
         for &(ref name, ref body) in self.exports.iter() {
             exports.push_str("obj.");
             exports.push_str(name);
@@ -146,12 +259,12 @@ impl Js {
             exports.push_str(";\n");
         }
         format!("
-            const function xform(obj) {{
+            function xform(obj) {{
                 {}
                 {}
                 return obj;
             }}
-            export const function instantiate(bytes, imports) {{
+            export function instantiate(bytes, imports) {{
                 return WebAssembly.instantiate(bytes, imports).then(xform);
             }}
         ", globals, exports)

crates/wasm-bindgen-cli-support/src/lib.rs

@@ -88,6 +88,7 @@ impl Object {
 
     pub fn generate_js(&self) -> String {
         let mut js = js::Js::default();
+        js.nodejs = self.nodejs;
         js.generate_program(&self.program);
         js.to_string()
     }

crates/wasm-bindgen-macro/src/ast.rs

@@ -24,7 +24,6 @@ pub enum Type {
 
 pub struct Struct {
     pub name: syn::Ident,
-    pub ctor: Option<Function>,
     pub methods: Vec<Method>,
     pub functions: Vec<Function>,
 }
@@ -118,16 +117,30 @@ impl Function {
         Function { name: input.ident, arguments, ret }
     }
 
-    pub fn export_name(&self) -> syn::Lit {
+    pub fn free_function_export_name(&self) -> syn::Lit {
+        let name = self.shared().free_function_export_name();
         syn::Lit {
-            value: syn::LitKind::Other(Literal::string(self.name.sym.as_str())),
+            value: syn::LitKind::Other(Literal::string(&name)),
             span: Default::default(),
         }
     }
 
-    pub fn rust_symbol(&self) -> syn::Ident {
-        let generated_name = format!("__wasm_bindgen_generated_{}",
-                                     self.name.sym.as_str());
+    pub fn struct_function_export_name(&self, s: syn::Ident) -> syn::Lit {
+        let name = self.shared().struct_function_export_name(s.sym.as_str());
+        syn::Lit {
+            value: syn::LitKind::Other(Literal::string(&name)),
+            span: Default::default(),
+        }
+    }
+
+    pub fn rust_symbol(&self, namespace: Option<syn::Ident>) -> syn::Ident {
+        let mut generated_name = format!("__wasm_bindgen_generated");
+        if let Some(ns) = namespace {
+            generated_name.push_str("_");
+            generated_name.push_str(ns.sym.as_str());
+        }
+        generated_name.push_str("_");
+        generated_name.push_str(self.name.sym.as_str());
         syn::Ident::from(generated_name)
     }
 
@@ -220,12 +233,15 @@ impl Struct {
     pub fn from(s: &syn::ItemStruct) -> Struct {
         Struct {
             name: s.ident,
-            ctor: None,
             methods: Vec::new(),
             functions: Vec::new(),
         }
     }
 
+    pub fn free_function(&self) -> syn::Ident {
+        syn::Ident::from(self.shared().free_function())
+    }
+
     pub fn push_item(&mut self, item: &syn::ImplItem) {
         let method = match *item {
             syn::ImplItem::Const(_) => panic!("const definitions aren't supported"),
@@ -299,7 +315,6 @@ impl Struct {
     pub fn shared(&self) -> shared::Struct {
         shared::Struct {
             name: self.name.to_string(),
-            ctor: self.ctor.as_ref().unwrap().shared(),
             functions: self.functions.iter().map(|f| f.shared()).collect(),
             methods: self.methods.iter().map(|f| f.shared()).collect(),
         }

crates/wasm-bindgen-macro/src/lib.rs

@@ -60,6 +60,7 @@ pub fn wasm_bindgen(input: TokenStream) -> TokenStream {
     static CNT: AtomicUsize = ATOMIC_USIZE_INIT;
     let generated_static_name = format!("__WASM_BINDGEN_GENERATED{}",
                                         CNT.fetch_add(1, Ordering::SeqCst));
+    let generated_static_name = syn::Ident::from(generated_static_name);
     let mut generated_static = String::from("wbg:");
     generated_static.push_str(&serde_json::to_string(&program.shared()).unwrap());
     let generated_static_value = syn::Lit {
@@ -75,22 +76,89 @@ pub fn wasm_bindgen(input: TokenStream) -> TokenStream {
             *#generated_static_value;
     }).to_tokens(&mut ret);
 
+    // println!("{}", ret);
+
     ret.into()
 }
 
 fn bindgen_fn(function: &ast::Function, into: &mut Tokens) {
-    let export_name = function.export_name();
-    let generated_name = function.rust_symbol();
+    bindgen(&function.free_function_export_name(),
+            function.rust_symbol(None),
+            Receiver::FreeFunction(function.name),
+            &function.arguments,
+            function.ret.as_ref(),
+            into)
+}
+
+fn bindgen_struct(s: &ast::Struct, into: &mut Tokens) {
+    for f in s.functions.iter() {
+        bindgen_struct_fn(s, f, into);
+    }
+    for f in s.methods.iter() {
+        bindgen_struct_method(s, f, into);
+    }
+
+    let name = &s.name;
+    let free_fn = s.free_function();
+    (quote! {
+        #[no_mangle]
+        pub unsafe extern fn #free_fn(ptr: *mut ::std::cell::RefCell<#name>) {
+            assert!(!ptr.is_null());
+            drop(Box::from_raw(ptr));
+        }
+    }).to_tokens(into);
+}
+
+fn bindgen_struct_fn(s: &ast::Struct, f: &ast::Function, into: &mut Tokens) {
+    bindgen(&f.struct_function_export_name(s.name),
+            f.rust_symbol(Some(s.name)),
+            Receiver::StructFunction(s.name, f.name),
+            &f.arguments,
+            f.ret.as_ref(),
+            into)
+}
+
+fn bindgen_struct_method(s: &ast::Struct, m: &ast::Method, into: &mut Tokens) {
+    bindgen(&m.function.struct_function_export_name(s.name),
+            m.function.rust_symbol(Some(s.name)),
+            Receiver::StructMethod(s.name, m.mutable, m.function.name),
+            &m.function.arguments,
+            m.function.ret.as_ref(),
+            into)
+}
+
+enum Receiver {
+    FreeFunction(syn::Ident),
+    StructFunction(syn::Ident, syn::Ident),
+    StructMethod(syn::Ident, bool, syn::Ident),
+}
+
+fn bindgen(export_name: &syn::Lit,
+           generated_name: syn::Ident,
+           receiver: Receiver,
+           arguments: &[ast::Type],
+           ret_type: Option<&ast::Type>,
+           into: &mut Tokens) {
     let mut args = vec![];
     let mut arg_conversions = vec![];
-    let real_name = &function.name;
     let mut converted_arguments = vec![];
     let ret = syn::Ident::from("_ret");
 
     let mut malloc = false;
     let mut boxed_str = false;
 
-    for (i, ty) in function.arguments.iter().enumerate() {
+    let mut offset = 0;
+    if let Receiver::StructMethod(class, _, _) = receiver {
+        args.push(quote! { me: *mut ::std::cell::RefCell<#class> });
+        arg_conversions.push(quote! {
+            assert!(!me.is_null());
+            let me = unsafe { &*me };
+        });
+        offset = 1;
+    }
+
+    for (i, ty) in arguments.iter().enumerate() {
+        let i = i + offset;
         let ident = syn::Ident::from(format!("arg{}", i));
         match *ty {
             ast::Type::Integer(i) => {
@@ -153,23 +221,23 @@ fn bindgen_fn(function: &ast::Function, into: &mut Tokens) {
     }
     let ret_ty;
     let convert_ret;
-    match function.ret {
-        Some(ast::Type::Integer(i)) => {
+    match ret_type {
+        Some(&ast::Type::Integer(i)) => {
             ret_ty = quote! { -> #i };
             convert_ret = quote! { #ret };
         }
-        Some(ast::Type::BorrowedStr) => panic!("can't return a borrowed string"),
-        Some(ast::Type::ByRef(_)) => panic!("can't return a borrowed ref"),
-        Some(ast::Type::ByMutRef(_)) => panic!("can't return a borrowed ref"),
-        Some(ast::Type::String) => {
+        Some(&ast::Type::BorrowedStr) => panic!("can't return a borrowed string"),
+        Some(&ast::Type::ByRef(_)) => panic!("can't return a borrowed ref"),
+        Some(&ast::Type::ByMutRef(_)) => panic!("can't return a borrowed ref"),
+        Some(&ast::Type::String) => {
             boxed_str = !BOXED_STR_GENERATED.swap(true, Ordering::SeqCst);
             ret_ty = quote! { -> *mut String };
             convert_ret = quote! { Box::into_raw(Box::new(#ret)) };
         }
-        Some(ast::Type::ByValue(name)) => {
+        Some(&ast::Type::ByValue(name)) => {
             ret_ty = quote! { -> *mut ::std::cell::RefCell<#name> };
             convert_ret = quote! {
-                Box::into_raw(Box::new(::std::cell::RefCell<#ret>))
+                Box::into_raw(Box::new(::std::cell::RefCell::new(#ret)))
             };
         }
         None => {
@@ -224,20 +292,38 @@ fn bindgen_fn(function: &ast::Function, into: &mut Tokens) {
         #malloc
         #boxed_str
 
-        #[no_mangle]
         #[export_name = #export_name]
+        #[allow(non_snake_case)]
         pub extern fn #generated_name(#(#args),*) #ret_ty {
             #(#arg_conversions)*
-            let #ret = #real_name(#(#converted_arguments),*);
+            let #ret = #receiver(#(#converted_arguments),*);
             #convert_ret
         }
     };
-    // println!("{}", tokens);
     tokens.to_tokens(into);
 }
 
-fn bindgen_struct(s: &ast::Struct, into: &mut Tokens) {
-    if s.ctor.is_none() {
-        panic!("struct `{}` needs a `new` function to construct it", s.name);
+impl ToTokens for Receiver {
+    fn to_tokens(&self, tokens: &mut Tokens) {
+        match *self {
+            Receiver::FreeFunction(name) => name.to_tokens(tokens),
+            Receiver::StructFunction(s, name) => {
+                s.to_tokens(tokens);
+                syn::tokens::Colon2::default().to_tokens(tokens);
+                name.to_tokens(tokens);
+            }
+            Receiver::StructMethod(_, mutable, name) => {
+                syn::Ident::from("me").to_tokens(tokens);
+                syn::tokens::Dot::default().to_tokens(tokens);
+                if mutable {
+                    syn::Ident::from("borrow_mut").to_tokens(tokens);
+                } else {
+                    syn::Ident::from("borrow").to_tokens(tokens);
+                }
+                tokens.append_delimited("(", Default::default(), |_| ());
+                syn::tokens::Dot::default().to_tokens(tokens);
+                name.to_tokens(tokens);
+            }
+        }
     }
 }

crates/wasm-bindgen-shared/src/lib.rs

@@ -10,7 +10,6 @@ pub struct Program {
 #[derive(Serialize, Deserialize)]
 pub struct Struct {
     pub name: String,
-    pub ctor: Function,
     pub functions: Vec<Function>,
     pub methods: Vec<Method>,
 }
@@ -28,6 +27,33 @@ pub struct Function {
     pub ret: Option<Type>,
 }
 
+impl Struct {
+    pub fn free_function(&self) -> String {
+        let mut name = format!("__wbindgen_");
+        name.extend(self.name
+            .chars()
+            .flat_map(|s| s.to_lowercase()));
+        name.push_str("_free");
+        return name
+    }
+}
+
+impl Function {
+    pub fn free_function_export_name(&self) -> String {
+        self.name.clone()
+    }
+
+    pub fn struct_function_export_name(&self, struct_: &str) -> String {
+        let mut name = struct_
+            .chars()
+            .flat_map(|s| s.to_lowercase())
+            .collect::<String>();
+        name.push_str("_");
+        name.push_str(&self.name);
+        return name
+    }
+}
+
 #[derive(Serialize, Deserialize)]
 pub enum Type {
     Number,

tests/classes.rs

@@ -21,7 +21,7 @@ fn simple() {
                     }
 
                     pub fn with_contents(a: u32) -> Foo {
-                        Foo::with_contents(a)
+                        Foo { contents: a }
                     }
 
                     pub fn add(&mut self, amt: u32) -> u32 {
@@ -35,15 +35,72 @@ fn simple() {
             import * as assert from "assert";
 
             export function test(wasm) {
-                const r = new wasm.Foo();
+                const r = wasm.Foo.new();
                 assert.strictEqual(r.add(0), 0);
                 assert.strictEqual(r.add(1), 1);
                 assert.strictEqual(r.add(1), 2);
+                r.free();
 
                 const r2 = wasm.Foo.with_contents(10);
-                assert.strictEqual(r.add(1), 11);
-                assert.strictEqual(r.add(2), 13);
-                assert.strictEqual(r.add(3), 16);
+                assert.strictEqual(r2.add(1), 11);
+                assert.strictEqual(r2.add(2), 13);
+                assert.strictEqual(r2.add(3), 16);
+                r2.free();
+            }
+        "#)
+        .test();
+}
+
+#[test]
+fn strings() {
+    test_support::project()
+        .file("src/lib.rs", r#"
+            #![feature(proc_macro)]
+
+            extern crate wasm_bindgen;
+
+            use wasm_bindgen::prelude::*;
+
+            wasm_bindgen! {
+                pub struct Foo {
+                    name: u32,
+                }
+
+                pub struct Bar {
+                    contents: String,
+                }
+
+                impl Foo {
+                    pub fn new() -> Foo {
+                        Foo { name: 0 }
+                    }
+
+                    pub fn set(&mut self, amt: u32) {
+                        self.name = amt;
+                    }
+
+                    pub fn bar(&self, mix: &str) -> Bar {
+                        Bar { contents: format!("foo-{}-{}", mix, self.name) }
+                    }
+                }
+
+                impl Bar {
+                    pub fn name(&self) -> String {
+                        self.contents.clone()
+                    }
+                }
+            }
+        "#)
+        .file("test.js", r#"
+            import * as assert from "assert";
+
+            export function test(wasm) {
+                const r = wasm.Foo.new();
+                r.set(3);
+                let bar = r.bar('baz');
+                r.free();
+                assert.strictEqual(bar.name(), "foo-baz-3");
+                bar.free();
             }
         "#)
         .test();