Implement RFC #2 - casting hierarchy between JS values

crates/backend/src/ast.rs

@@ -127,6 +127,8 @@ pub struct ImportType {
     pub name: Ident,
     pub attrs: Vec<syn::Attribute>,
     pub doc_comment: Option<String>,
+    pub instanceof_shim: String,
+    pub extends: Vec<Ident>,
 }
 
 #[cfg_attr(feature = "extra-traits", derive(Debug, PartialEq, Eq))]
@@ -408,7 +410,10 @@ impl ImportStatic {
 
 impl ImportType {
     fn shared(&self) -> shared::ImportType {
-        shared::ImportType {}
+        shared::ImportType {
+            name: self.name.to_string(),
+            instanceof_shim: self.instanceof_shim.clone(),
+        }
     }
 }
 

crates/backend/src/codegen.rs

@@ -519,93 +519,168 @@ impl ToTokens for ast::ImportType {
             None => "",
             Some(comment) => comment,
         };
+        let const_name = format!("__wbg_generated_const_{}", name);
+        let const_name = Ident::new(&const_name, Span::call_site());
+        let instanceof_shim = Ident::new(&self.instanceof_shim, Span::call_site());
         (quote! {
             #[allow(bad_style)]
             #(#attrs)*
             #[doc = #doc_comment]
+            #[repr(transparent)]
             #vis struct #name {
                 obj: ::wasm_bindgen::JsValue,
             }
 
-            impl ::wasm_bindgen::describe::WasmDescribe for #name {
-                fn describe() {
-                    ::wasm_bindgen::JsValue::describe();
+            #[allow(bad_style)]
+            const #const_name: () = {
+                use wasm_bindgen::convert::{IntoWasmAbi, FromWasmAbi, Stack};
+                use wasm_bindgen::convert::{OptionIntoWasmAbi, OptionFromWasmAbi};
+                use wasm_bindgen::convert::{RefFromWasmAbi, GlobalStack};
+                use wasm_bindgen::describe::WasmDescribe;
+                use wasm_bindgen::{JsValue, JsCast};
+                use wasm_bindgen::__rt::core::mem::ManuallyDrop;
+
+                impl WasmDescribe for #name {
+                    fn describe() {
+                        JsValue::describe();
+                    }
                 }
-            }
 
-            impl ::wasm_bindgen::convert::IntoWasmAbi for #name {
-                type Abi = <::wasm_bindgen::JsValue as
-                    ::wasm_bindgen::convert::IntoWasmAbi>::Abi;
+                impl IntoWasmAbi for #name {
+                    type Abi = <JsValue as IntoWasmAbi>::Abi;
 
-                fn into_abi(self, extra: &mut ::wasm_bindgen::convert::Stack) -> Self::Abi {
-                    self.obj.into_abi(extra)
+                    fn into_abi(self, extra: &mut Stack) -> Self::Abi {
+                        self.obj.into_abi(extra)
+                    }
                 }
-            }
 
-            impl ::wasm_bindgen::convert::OptionIntoWasmAbi for #name {
-                fn none() -> Self::Abi { 0 }
-            }
+                impl OptionIntoWasmAbi for #name {
+                    fn none() -> Self::Abi { 0 }
+                }
 
-            impl<'a> ::wasm_bindgen::convert::OptionIntoWasmAbi for &'a #name {
-                fn none() -> Self::Abi { 0 }
-            }
+                impl<'a> OptionIntoWasmAbi for &'a #name {
+                    fn none() -> Self::Abi { 0 }
+                }
 
-            impl ::wasm_bindgen::convert::FromWasmAbi for #name {
-                type Abi = <::wasm_bindgen::JsValue as
-                    ::wasm_bindgen::convert::FromWasmAbi>::Abi;
+                impl FromWasmAbi for #name {
+                    type Abi = <JsValue as FromWasmAbi>::Abi;
 
-                unsafe fn from_abi(
-                    js: Self::Abi,
-                    extra: &mut ::wasm_bindgen::convert::Stack,
-                ) -> Self {
-                    #name {
-                        obj: ::wasm_bindgen::JsValue::from_abi(js, extra),
+                    unsafe fn from_abi(js: Self::Abi, extra: &mut Stack) -> Self {
+                        #name {
+                            obj: JsValue::from_abi(js, extra),
+                        }
                     }
                 }
-            }
 
-            impl ::wasm_bindgen::convert::OptionFromWasmAbi for #name {
-                fn is_none(abi: &Self::Abi) -> bool { *abi == 0 }
-            }
+                impl OptionFromWasmAbi for #name {
+                    fn is_none(abi: &Self::Abi) -> bool { *abi == 0 }
+                }
 
-            impl<'a> ::wasm_bindgen::convert::IntoWasmAbi for &'a #name {
-                type Abi = <&'a ::wasm_bindgen::JsValue as
-                    ::wasm_bindgen::convert::IntoWasmAbi>::Abi;
+                impl<'a> IntoWasmAbi for &'a #name {
+                    type Abi = <&'a JsValue as IntoWasmAbi>::Abi;
 
-                fn into_abi(self, extra: &mut ::wasm_bindgen::convert::Stack) -> Self::Abi {
-                    (&self.obj).into_abi(extra)
+                    fn into_abi(self, extra: &mut Stack) -> Self::Abi {
+                        (&self.obj).into_abi(extra)
+                    }
                 }
-            }
 
-            impl ::wasm_bindgen::convert::RefFromWasmAbi for #name {
-                type Abi = <::wasm_bindgen::JsValue as
-                    ::wasm_bindgen::convert::RefFromWasmAbi>::Abi;
-                type Anchor = ::wasm_bindgen::__rt::core::mem::ManuallyDrop<#name>;
+                impl RefFromWasmAbi for #name {
+                    type Abi = <JsValue as RefFromWasmAbi>::Abi;
+                    type Anchor = ManuallyDrop<#name>;
 
-                unsafe fn ref_from_abi(
-                    js: Self::Abi,
-                    extra: &mut ::wasm_bindgen::convert::Stack,
-                ) -> Self::Anchor {
-                    let tmp = <::wasm_bindgen::JsValue as ::wasm_bindgen::convert::RefFromWasmAbi>
-                        ::ref_from_abi(js, extra);
-                    ::wasm_bindgen::__rt::core::mem::ManuallyDrop::new(#name {
-                        obj: ::wasm_bindgen::__rt::core::mem::ManuallyDrop::into_inner(tmp),
-                    })
+                    unsafe fn ref_from_abi(js: Self::Abi, extra: &mut Stack) -> Self::Anchor {
+                        let tmp = <JsValue as RefFromWasmAbi>::ref_from_abi(js, extra);
+                        ManuallyDrop::new(#name {
+                            obj: ManuallyDrop::into_inner(tmp),
+                        })
+                    }
                 }
-            }
 
-            impl From<::wasm_bindgen::JsValue> for #name {
-                fn from(obj: ::wasm_bindgen::JsValue) -> #name {
-                    #name { obj }
+                // TODO: remove this on the next major version
+                impl From<JsValue> for #name {
+                    fn from(obj: JsValue) -> #name {
+                        #name { obj }
+                    }
                 }
-            }
 
-            impl From<#name> for ::wasm_bindgen::JsValue {
-                fn from(obj: #name) -> ::wasm_bindgen::JsValue {
-                    obj.obj
+                impl AsRef<JsValue> for #name {
+                    fn as_ref(&self) -> &JsValue { &self.obj }
                 }
-            }
+
+                impl AsMut<JsValue> for #name {
+                    fn as_mut(&mut self) -> &mut JsValue { &mut self.obj }
+                }
+
+                impl From<#name> for JsValue {
+                    fn from(obj: #name) -> JsValue {
+                        obj.obj
+                    }
+                }
+
+                impl JsCast for #name {
+                    #[cfg(all(target_arch = "wasm32", not(target_os = "emscripten")))]
+                    fn instanceof(val: &JsValue) -> bool {
+                        #[link(wasm_import_module = "__wbindgen_placeholder__")]
+                        extern {
+                            fn #instanceof_shim(val: u32) -> u32;
+                        }
+                        unsafe {
+                            let idx = val.into_abi(&mut GlobalStack::new());
+                            #instanceof_shim(idx) != 0
+                        }
+                    }
+
+                    #[cfg(not(all(target_arch = "wasm32", not(target_os = "emscripten"))))]
+                    fn instanceof(val: &JsValue) -> bool {
+                        drop(val);
+                        panic!("cannot check instanceof on non-wasm targets");
+                    }
+
+                    fn unchecked_from_js(val: JsValue) -> Self {
+                        #name { obj: val }
+                    }
+
+                    fn unchecked_from_js_ref(val: &JsValue) -> &Self {
+                        // Should be safe because `#name` is a transparent
+                        // wrapper around `val`
+                        unsafe { &*(val as *const JsValue as *const #name) }
+                    }
+
+                    fn unchecked_from_js_mut(val: &mut JsValue) -> &mut Self {
+                        // Should be safe because `#name` is a transparent
+                        // wrapper around `val`
+                        unsafe { &mut *(val as *mut JsValue as *mut #name) }
+                    }
+                }
+
+                ()
+            };
         }).to_tokens(tokens);
+
+        for superclass in self.extends.iter() {
+            (quote! {
+                impl From<#name> for #superclass {
+                    fn from(obj: #name) -> #superclass {
+                        use wasm_bindgen::JsCast;
+                        #superclass::unchecked_from_js(obj.into())
+                    }
+                }
+
+                impl AsRef<#superclass> for #name {
+                    fn as_ref(&self) -> &#superclass {
+                        use wasm_bindgen::JsCast;
+                        #superclass::unchecked_from_js_ref(self.as_ref())
+                    }
+                }
+
+                impl AsMut<#superclass> for #name {
+                    fn as_mut(&mut self) -> &mut #superclass {
+                        use wasm_bindgen::JsCast;
+                        #superclass::unchecked_from_js_mut(self.as_mut())
+                    }
+                }
+            }).to_tokens(tokens);
+        }
     }
 }
 

crates/cli-support/src/js/mod.rs

@@ -1755,7 +1755,14 @@ impl<'a, 'b> SubContext<'a, 'b> {
                     format!("failed to generate bindings for JS import `{}`", s.name)
                 })?;
             }
-            shared::ImportKind::Type(_) => {}
+            shared::ImportKind::Type(ref ty) => {
+                self.generate_import_type(import, ty).with_context(|_| {
+                    format!(
+                        "failed to generate bindings for JS import `{}`",
+                        ty.name,
+                    )
+                })?;
+            }
             shared::ImportKind::Enum(_) => {}
         }
         Ok(())
@@ -1936,6 +1943,27 @@ impl<'a, 'b> SubContext<'a, 'b> {
         Ok(())
     }
 
+    fn generate_import_type(
+        &mut self,
+        info: &shared::Import,
+        import: &shared::ImportType,
+    ) -> Result<(), Error> {
+        if !self.cx.wasm_import_needed(&import.instanceof_shim) {
+            return Ok(());
+        }
+        let name = self.import_name(info, &import.name)?;
+        self.cx.expose_get_object();
+        let body = format!("
+                function(idx) {{
+                    return getObject(idx) instanceof {} ? 1 : 0;
+                }}
+            ",
+            name,
+        );
+        self.cx.export(&import.instanceof_shim, &body, None);
+        Ok(())
+    }
+
     fn generate_enum(&mut self, enum_: &shared::Enum) {
         let mut variants = String::new();
 

crates/macro-support/src/parser.rs

@@ -182,6 +182,16 @@ impl BindgenAttrs {
             })
             .next()
     }
+
+    /// Return the list of classes that a type extends
+    fn extends(&self) -> impl Iterator<Item = &Ident> {
+        self.attrs
+            .iter()
+            .filter_map(|a| match a {
+                BindgenAttr::Extends(s) => Some(s),
+                _ => None,
+            })
+    }
 }
 
 impl syn::synom::Synom for BindgenAttrs {
@@ -217,6 +227,7 @@ pub enum BindgenAttr {
     Readonly,
     JsName(String),
     JsClass(String),
+    Extends(Ident),
 }
 
 impl syn::synom::Synom for BindgenAttr {
@@ -295,6 +306,13 @@ impl syn::synom::Synom for BindgenAttr {
             s: syn!(syn::LitStr) >>
             (s.value())
         )=> { BindgenAttr::JsClass }
+        |
+        do_parse!(
+            call!(term, "extends") >>
+            punct!(=) >>
+            ns: call!(term2ident) >>
+            (ns)
+        )=> { BindgenAttr::Extends }
     ));
 }
 
@@ -520,15 +538,18 @@ impl<'a> ConvertToAst<(BindgenAttrs, &'a Option<String>)> for syn::ForeignItemFn
     }
 }
 
-impl ConvertToAst<()> for syn::ForeignItemType {
+impl ConvertToAst<BindgenAttrs> for syn::ForeignItemType {
     type Target = ast::ImportKind;
 
-    fn convert(self, (): ()) -> Result<Self::Target, Diagnostic> {
+    fn convert(self, attrs: BindgenAttrs) -> Result<Self::Target, Diagnostic> {
+        let shim = format!("__wbg_instanceof_{}_{}", self.ident, ShortHash(&self.ident));
         Ok(ast::ImportKind::Type(ast::ImportType {
             vis: self.vis,
-            name: self.ident,
             attrs: self.attrs,
             doc_comment: None,
+            instanceof_shim: shim,
+            name: self.ident,
+            extends: attrs.extends().cloned().collect(),
         }))
     }
 }
@@ -935,7 +956,7 @@ impl<'a> MacroParse<&'a BindgenAttrs> for syn::ForeignItem {
         let js_namespace = item_opts.js_namespace().or(opts.js_namespace()).cloned();
         let kind = match self {
             syn::ForeignItem::Fn(f) => f.convert((item_opts, &module))?,
-            syn::ForeignItem::Type(t) => t.convert(())?,
+            syn::ForeignItem::Type(t) => t.convert(item_opts)?,
             syn::ForeignItem::Static(s) => s.convert(item_opts)?,
             _ => panic!("only foreign functions/types allowed for now"),
         };

crates/shared/src/lib.rs

@@ -3,7 +3,7 @@
 #[macro_use]
 extern crate serde_derive;
 
-pub const SCHEMA_VERSION: &str = "7";
+pub const SCHEMA_VERSION: &str = "8";
 
 #[derive(Deserialize)]
 pub struct ProgramOnlySchema {
@@ -81,7 +81,10 @@ pub struct ImportStatic {
 }
 
 #[derive(Deserialize, Serialize)]
-pub struct ImportType {}
+pub struct ImportType {
+    pub name: String,
+    pub instanceof_shim: String,
+}
 
 #[derive(Deserialize, Serialize)]
 pub struct ImportEnum {}