Merge pull request #127 from konstin/new

Support `new Foo(...)` to fix #115

Author: alexcrichton

DESIGN.md

@@ -536,31 +536,37 @@ available to JS through generated shims. If we take a look at the generated JS
 code for this we'll see:
 
 ```js
-import * as wasm from './foo_bg';
+import * as wasm from './js_hello_world_bg';
 
 export class Foo {
-  constructor(ptr) {
-    this.ptr = ptr;
-  }
+    static __construct(ptr) {
+        return new Foo(ptr);
+    }
 
-  free() {
-    const ptr = this.ptr;
-    this.ptr = 0;
-    wasm.__wbindgen_foo_free(ptr);
-  }
+    constructor(ptr) {
+        this.ptr = ptr;
+    }
 
-  static new(arg0) {
-    const ret = wasm.foo_new(arg0);
-    return new Foo(ret);
-  }
+    free() {
+        const ptr = this.ptr;
+        this.ptr = 0;
+        wasm.__wbg_foo_free(ptr);
+    }
 
-  get() {
-    return wasm.foo_get(this.ptr);
-  }
+    static new(arg0) {
+        const ret = wasm.foo_new(arg0);
+        return Foo.__construct(ret)
+    }
 
-  set(arg0) {
-    wasm.foo_set(this.ptr, arg0);
-  }
+    get() {
+        const ret = wasm.foo_get(this.ptr);
+        return ret;
+    }
+
+    set(arg0) {
+        const ret = wasm.foo_set(this.ptr, arg0);
+        return ret;
+    }
 }
 ```
 
@@ -573,9 +579,7 @@ to JS:
 * Manual memory management is exposed in JS as well. The `free` function is
   required to be invoked to deallocate resources on the Rust side of things.
 
-It's intended that `new Foo()` is never used in JS. When `wasm-bindgen` is run
-with `--debug` it'll actually emit assertions to this effect to ensure that
-instances of `Foo` are only constructed with the functions like `Foo.new` in JS.
+To be able to use `new Foo()`, you'd need to annotate `new` as `#[wasm_bindgen(constructor)]`.
 
 One important aspect to note here, though, is that once `free` is called the JS
 object is "neutered" in that its internal pointer is nulled out. This means that

crates/backend/src/ast.rs

@@ -14,6 +14,7 @@ pub struct Export {
     pub class: Option<syn::Ident>,
     pub method: bool,
     pub mutable: bool,
+    pub constructor: Option<String>,
     pub function: Function,
 }
 
@@ -116,6 +117,7 @@ impl Program {
                     class: None,
                     method: false,
                     mutable: false,
+                    constructor: None,
                     function: Function::from(f, opts),
                 });
             }
@@ -126,8 +128,8 @@ impl Program {
             }
             syn::Item::Impl(mut i) => {
                 let opts = opts.unwrap_or_else(|| BindgenAttrs::find(&mut i.attrs));
+                self.push_impl(&mut i, opts);
                 i.to_tokens(tokens);
-                self.push_impl(i, opts);
             }
             syn::Item::ForeignMod(mut f) => {
                 let opts = opts.unwrap_or_else(|| BindgenAttrs::find(&mut f.attrs));
@@ -145,7 +147,7 @@ impl Program {
         }
     }
 
-    pub fn push_impl(&mut self, item: syn::ItemImpl, _opts: BindgenAttrs) {
+    pub fn push_impl(&mut self, item: &mut syn::ItemImpl, _opts: BindgenAttrs) {
         if item.defaultness.is_some() {
             panic!("default impls are not supported");
         }
@@ -168,16 +170,16 @@ impl Program {
             },
             _ => panic!("unsupported self type in impl"),
         };
-        for item in item.items.into_iter() {
-            self.push_impl_item(name, item);
+        for mut item in item.items.iter_mut() {
+            self.push_impl_item(name, &mut item);
         }
     }
 
-    fn push_impl_item(&mut self, class: syn::Ident, item: syn::ImplItem) {
-        let mut method = match item {
+    fn push_impl_item(&mut self, class: syn::Ident, item: &mut syn::ImplItem) {
+        let method = match item {
             syn::ImplItem::Const(_) => panic!("const definitions aren't supported"),
             syn::ImplItem::Type(_) => panic!("type definitions in impls aren't supported"),
-            syn::ImplItem::Method(m) => m,
+            syn::ImplItem::Method(ref mut m) => m,
             syn::ImplItem::Macro(_) => panic!("macros in impls aren't supported"),
             syn::ImplItem::Verbatim(_) => panic!("unparsed impl item?"),
         };
@@ -196,19 +198,27 @@ impl Program {
         }
 
         let opts = BindgenAttrs::find(&mut method.attrs);
+        let is_constructor = opts.constructor();
+        let constructor = if is_constructor {
+            Some(method.sig.ident.to_string())
+        } else {
+            None
+        };
 
         let (function, mutable) = Function::from_decl(
             method.sig.ident,
-            Box::new(method.sig.decl),
-            method.attrs,
+            Box::new(method.sig.decl.clone()),
+            method.attrs.clone(),
             opts,
-            method.vis,
+            method.vis.clone(),
             true,
         );
+
         self.exports.push(Export {
             class: Some(class),
             method: mutable.is_some(),
             mutable: mutable.unwrap_or(false),
+            constructor,
             function,
         });
     }
@@ -536,6 +546,7 @@ impl Export {
         shared::Export {
             class: self.class.map(|s| s.as_ref().to_string()),
             method: self.method,
+            constructor: self.constructor.clone(),
             function: self.function.shared(),
         }
     }
@@ -764,6 +775,7 @@ impl syn::synom::Synom for BindgenAttrs {
     ));
 }
 
+#[derive(PartialEq)]
 enum BindgenAttr {
     Catch,
     Constructor,

crates/cli-support/src/js.rs

@@ -29,6 +29,7 @@ pub struct Context<'a> {
 pub struct ExportedClass {
     pub contents: String,
     pub typescript: String,
+    pub constructor: Option<String>,
 }
 
 pub struct SubContext<'a, 'b: 'a> {
@@ -316,42 +317,57 @@ impl<'a> Context<'a> {
             ts_dst.push_str("
                 public ptr: number;
             ");
-            if self.config.debug {
-                self.expose_check_token();
+
+            if self.config.debug || exports.constructor.is_some() {
+                self.expose_constructor_token();
+
                 dst.push_str(&format!("
-                    constructor(ptr, sym) {{
-                        _checkToken(sym);
-                        this.ptr = ptr;
+                    static __construct(ptr) {{
+                        return new {}(new ConstructorToken(ptr));
                     }}
-                "));
-                ts_dst.push_str("constructor(ptr: number, sym: Symbol);\n");
-
-                let new_name = shared::new_function(&class);
-                if self.wasm_import_needed(&new_name) {
-                    self.expose_add_heap_object();
-                    self.export(&new_name, &format!("
-                        function(ptr) {{
-                            return addHeapObject(new {class}(ptr, token));
+
+                    constructor(...args) {{
+                        if (args.length === 1 && args[0] instanceof ConstructorToken) {{
+                            this.ptr = args[0].ptr;
+                            return;
                         }}
-                    ", class = class));
+                ", class));
+
+                if let Some(constructor) = exports.constructor {
+                    ts_dst.push_str(&format!("constructor(...args: [any]);\n"));
+
+                    dst.push_str(&format!("
+                        // This invocation of new will call this constructor with a ConstructorToken
+                        let instance = {class}.{constructor}(...args);
+                        this.ptr = instance.ptr;
+                    ", class = class, constructor = constructor));
+                } else {
+                    dst.push_str("throw new Error('you cannot invoke `new` directly without having a \
+                method annotated a constructor');");
                 }
+
+                dst.push_str("}");
             } else {
                 dst.push_str(&format!("
+                    static __construct(ptr) {{
+                        return new {}(ptr);
+                    }}
+
                     constructor(ptr) {{
                         this.ptr = ptr;
                     }}
-                "));
-                ts_dst.push_str("constructor(ptr: number);\n");
-
-                let new_name = shared::new_function(&class);
-                if self.wasm_import_needed(&new_name) {
-                    self.expose_add_heap_object();
-                    self.export(&new_name, &format!("
-                        function(ptr) {{
-                            return addHeapObject(new {class}(ptr));
-                        }}
-                    ", class = class));
-                }
+                ", class));
+            }
+
+            let new_name = shared::new_function(&class);
+            if self.wasm_import_needed(&new_name) {
+                self.expose_add_heap_object();
+
+                self.export(&new_name, &format!("
+                    function(ptr) {{
+                        return addHeapObject({}.__construct(ptr));
+                    }}
+                ", class));
             }
 
             dst.push_str(&format!("
@@ -589,19 +605,6 @@ impl<'a> Context<'a> {
         ", get_obj));
     }
 
-    fn expose_check_token(&mut self) {
-        if !self.exposed_globals.insert("check_token") {
-            return;
-        }
-        self.globals.push_str(&format!("
-            const token = Symbol('foo');
-            function _checkToken(sym) {{
-                if (token !== sym)
-                    throw new Error('cannot invoke `new` directly');
-            }}
-        "));
-    }
-
     fn expose_assert_num(&mut self) {
         if !self.exposed_globals.insert("assert_num") {
             return;
@@ -765,6 +768,20 @@ impl<'a> Context<'a> {
         "));
     }
 
+    fn expose_constructor_token(&mut self) {
+        if !self.exposed_globals.insert("ConstructorToken") {
+            return;
+        }
+
+        self.globals.push_str("
+            class ConstructorToken {
+                constructor(ptr) {
+                    this.ptr = ptr;
+                }
+            }
+        ");
+    }
+
     fn expose_get_string_from_wasm(&mut self) {
         if !self.exposed_globals.insert("get_string_from_wasm") {
             return;
@@ -1236,11 +1253,8 @@ impl<'a> Context<'a> {
         if let Some(name) = ty.rust_struct() {
             dst_ts.push_str(": ");
             dst_ts.push_str(name);
-            return if self.config.debug {
-                format!("return new {name}(ret, token);", name = name)
-            } else {
-                format!("return new {name}(ret);", name = name)
-            }
+
+            return format!("return {}.__construct(ret)",&name);
         }
 
         if ty.is_number() {
@@ -1324,8 +1338,8 @@ impl<'a, 'b> SubContext<'a, 'b> {
         self.cx.typescript.push_str("\n");
     }
 
-    pub fn generate_export_for_class(&mut self, class: &str, export: &shared::Export) {
-        let wasm_name = shared::struct_function_export_name(class, &export.function.name);
+    pub fn generate_export_for_class(&mut self, class_name: &str, export: &shared::Export) {
+        let wasm_name = shared::struct_function_export_name(class_name, &export.function.name);
         let descriptor = self.cx.describe(&wasm_name);
         let (js, ts) = self.generate_function(
             "",
@@ -1334,12 +1348,26 @@ impl<'a, 'b> SubContext<'a, 'b> {
             export.method,
             &descriptor.unwrap_function(),
         );
-        let class = self.cx.exported_classes.entry(class.to_string())
+
+        let class = self.cx.exported_classes.entry(class_name.to_string())
             .or_insert(ExportedClass::default());
         if !export.method {
             class.contents.push_str("static ");
             class.typescript.push_str("static ");
         }
+
+        let constructors: Vec<String> = self.program.exports
+            .iter()
+            .filter(|x| x.class == Some(class_name.to_string()))
+            .filter_map(|x| x.constructor.clone())
+            .collect();
+
+        class.constructor = match constructors.len() {
+            0 => None,
+            1 => Some(constructors[0].clone()),
+            x @ _ => panic!("There must be only one constructor, not {}", x),
+        };
+
         class.contents.push_str(&export.function.name);
         class.contents.push_str(&js);
         class.contents.push_str("\n");
@@ -1560,15 +1588,11 @@ impl<'a, 'b> SubContext<'a, 'b> {
                 continue
             }
 
-            if let Some(s) = arg.rust_struct() {
+            if let Some(class) = arg.rust_struct() {
                 if arg.is_by_ref() {
                     panic!("cannot invoke JS functions with custom ref types yet")
                 }
-                let assign = if self.cx.config.debug {
-                    format!("let c{0} = new {class}(arg{0}, token);", i, class = s)
-                } else {
-                    format!("let c{0} = new {class}(arg{0});", i, class = s)
-                };
+                let assign = format!("let c{0} = {1}.__construct(arg{0});", i, class);
                 extra.push_str(&assign);
                 invoc_args.push(format!("c{}", i));
                 continue

crates/shared/src/lib.rs

@@ -54,6 +54,7 @@ pub struct ImportType {
 pub struct Export {
     pub class: Option<String>,
     pub method: bool,
+    pub constructor: Option<String>,
     pub function: Function,
 }