Deprecate JsStatic in favor of #[wasm_bindgen(thread_local)]`

Removed `impl Deref for JsStatic` when compiling with `cfg(target_feature = "atomics")`, which was unsound.

CHANGELOG.md

@@ -72,7 +72,7 @@
 * Added an experimental Node.JS ES module target, in comparison the current `node` target uses CommonJS, with `--target experimental-nodejs-module` or when testing with `wasm_bindgen_test_configure!(run_in_node_experimental)`.
   [#4027](https://github.com/rustwasm/wasm-bindgen/pull/4027)
 
-* Added importing strings as `JsString` through `#[wasm_bindgen(static_string)] static STRING: JsString = "a string literal";`.
+* Added importing strings as `JsString` through `#[wasm_bindgen(thread_local, static_string)] static STRING: JsString = "a string literal";`.
   [#4055](https://github.com/rustwasm/wasm-bindgen/pull/4055)
 
 ### Changed
@@ -129,6 +129,12 @@
 * Filtered files in published crates, significantly reducing the package size and notably excluding any bash files.
   [#4046](https://github.com/rustwasm/wasm-bindgen/pull/4046)
 
+* Deprecated `JsStatic` in favor of `#[wasm_bindgen(thread_local)]`, which creates a `std::thread::LocalKey`. The syntax is otherwise the same.
+  [#4057](https://github.com/rustwasm/wasm-bindgen/pull/4057)
+
+* Removed `impl Deref for JsStatic` when compiling with `cfg(target_feature = "atomics")`, which was unsound.
+  [#4057](https://github.com/rustwasm/wasm-bindgen/pull/4057)
+
 ### Fixed
 
 * Copy port from headless test server when using `WASM_BINDGEN_TEST_ADDRESS`.

crates/backend/src/ast.rs

@@ -275,6 +275,8 @@ pub struct ImportStatic {
     pub js_name: String,
     /// Path to wasm_bindgen
     pub wasm_bindgen: Path,
+    /// [`true`] if using the new `thread_local` representation.
+    pub thread_local: bool,
 }
 
 /// The type of a static string being imported

crates/backend/src/codegen.rs

@@ -1645,15 +1645,42 @@ impl ToTokens for ast::Enum {
 impl ToTokens for ast::ImportStatic {
     fn to_tokens(&self, into: &mut TokenStream) {
         let ty = &self.ty;
-        static_import(
-            &self.vis,
-            &self.rust_name,
-            &self.wasm_bindgen,
-            ty,
-            ty,
-            &self.shim,
-        )
-        .to_tokens(into);
+
+        if self.thread_local {
+            thread_local_import(
+                &self.vis,
+                &self.rust_name,
+                &self.wasm_bindgen,
+                ty,
+                ty,
+                &self.shim,
+            )
+            .to_tokens(into)
+        } else {
+            let vis = &self.vis;
+            let name = &self.rust_name;
+            let wasm_bindgen = &self.wasm_bindgen;
+            let ty = &self.ty;
+            let shim_name = &self.shim;
+            let init = static_init(wasm_bindgen, ty, shim_name);
+
+            into.extend(quote! {
+                #[automatically_derived]
+                #[deprecated = "use with `#[wasm_bindgen(thread_local)]` instead"]
+            });
+            into.extend(
+                quote_spanned! { name.span() => #vis static #name: #wasm_bindgen::JsStatic<#ty> = {
+                        fn init() -> #ty {
+                            #init
+                        }
+                        thread_local!(static _VAL: #ty = init(););
+                        #wasm_bindgen::JsStatic {
+                            __inner: &_VAL,
+                        }
+                    };
+                },
+            );
+        }
 
         Descriptor {
             ident: &self.shim,
@@ -1672,7 +1699,7 @@ impl ToTokens for ast::ImportString {
         let js_sys = &self.js_sys;
         let actual_ty: syn::Type = parse_quote!(#js_sys::JsString);
 
-        static_import(
+        thread_local_import(
             &self.vis,
             &self.rust_name,
             &self.wasm_bindgen,
@@ -1684,41 +1711,45 @@ impl ToTokens for ast::ImportString {
     }
 }
 
-fn static_import(
+fn thread_local_import(
     vis: &syn::Visibility,
     name: &Ident,
     wasm_bindgen: &syn::Path,
     actual_ty: &syn::Type,
     ty: &syn::Type,
     shim_name: &Ident,
 ) -> TokenStream {
+    let init = static_init(wasm_bindgen, ty, shim_name);
+
+    quote! {
+        thread_local! {
+            #[automatically_derived]
+            #vis static #name: #actual_ty = {
+                #init
+            };
+        }
+    }
+}
+
+fn static_init(wasm_bindgen: &syn::Path, ty: &syn::Type, shim_name: &Ident) -> TokenStream {
     let abi_ret = quote! {
         #wasm_bindgen::convert::WasmRet<<#ty as #wasm_bindgen::convert::FromWasmAbi>::Abi>
     };
     quote! {
-        #[automatically_derived]
-        #vis static #name: #wasm_bindgen::JsStatic<#actual_ty> = {
-            fn init() -> #ty {
-                #[link(wasm_import_module = "__wbindgen_placeholder__")]
-                #[cfg(all(target_arch = "wasm32", target_os = "unknown"))]
-                extern "C" {
-                    fn #shim_name() -> #abi_ret;
-                }
+        #[link(wasm_import_module = "__wbindgen_placeholder__")]
+        #[cfg(all(target_arch = "wasm32", target_os = "unknown"))]
+        extern "C" {
+            fn #shim_name() -> #abi_ret;
+        }
 
-                #[cfg(not(all(target_arch = "wasm32", target_os = "unknown")))]
-                unsafe fn #shim_name() -> #abi_ret {
-                    panic!("cannot access imported statics on non-wasm targets")
-                }
+        #[cfg(not(all(target_arch = "wasm32", target_os = "unknown")))]
+        unsafe fn #shim_name() -> #abi_ret {
+            panic!("cannot access imported statics on non-wasm targets")
+        }
 
-                unsafe {
-                    <#ty as #wasm_bindgen::convert::FromWasmAbi>::from_abi(#shim_name().join())
-                }
-            }
-            thread_local!(static _VAL: #ty = init(););
-            #wasm_bindgen::JsStatic {
-                __inner: &_VAL,
-            }
-        };
+        unsafe {
+            <#ty as #wasm_bindgen::convert::FromWasmAbi>::from_abi(#shim_name().join())
+        }
     }
 }
 

crates/js-sys/tests/wasm/Function.rs

@@ -5,13 +5,13 @@ use wasm_bindgen_test::*;
 
 #[wasm_bindgen]
 extern "C" {
-    #[wasm_bindgen(js_name = max, js_namespace = Math)]
+    #[wasm_bindgen(thread_local, js_name = max, js_namespace = Math)]
     static MAX: Function;
 
     type ArrayPrototype;
     #[wasm_bindgen(method, getter, structural)]
     pub fn push(this: &ArrayPrototype) -> Function;
-    #[wasm_bindgen(js_name = prototype, js_namespace = Array)]
+    #[wasm_bindgen(thread_local, js_name = prototype, js_namespace = Array)]
     static ARRAY_PROTOTYPE2: ArrayPrototype;
 }
 
@@ -21,12 +21,19 @@ fn apply() {
     args.push(&1.into());
     args.push(&2.into());
     args.push(&3.into());
-    assert_eq!(MAX.apply(&JsValue::undefined(), &args).unwrap(), 3);
+    assert_eq!(
+        MAX.with(|max| max.apply(&JsValue::undefined(), &args))
+            .unwrap(),
+        3
+    );
 
     let arr = JsValue::from(Array::new());
     let args = Array::new();
     args.push(&1.into());
-    ARRAY_PROTOTYPE2.push().apply(&arr, &args).unwrap();
+    ARRAY_PROTOTYPE2
+        .with(ArrayPrototype::push)
+        .apply(&arr, &args)
+        .unwrap();
     assert_eq!(Array::from(&arr).length(), 1);
 }
 
@@ -111,24 +118,29 @@ fn bind3() {
 
 #[wasm_bindgen_test]
 fn length() {
-    assert_eq!(MAX.length(), 2);
-    assert_eq!(ARRAY_PROTOTYPE2.push().length(), 1);
+    assert_eq!(MAX.with(Function::length), 2);
+    assert_eq!(ARRAY_PROTOTYPE2.with(ArrayPrototype::push).length(), 1);
 }
 
 #[wasm_bindgen_test]
 fn name() {
-    assert_eq!(JsValue::from(MAX.name()), "max");
-    assert_eq!(JsValue::from(ARRAY_PROTOTYPE2.push().name()), "push");
+    assert_eq!(JsValue::from(MAX.with(Function::name)), "max");
+    assert_eq!(
+        JsValue::from(ARRAY_PROTOTYPE2.with(ArrayPrototype::push).name()),
+        "push"
+    );
 }
 
 #[wasm_bindgen_test]
 fn to_string() {
-    assert!(MAX.to_string().length() > 0);
+    assert!(MAX.with(Function::to_string).length() > 0);
 }
 
 #[wasm_bindgen_test]
 fn function_inheritance() {
-    assert!(MAX.is_instance_of::<Function>());
-    assert!(MAX.is_instance_of::<Object>());
-    let _: &Object = MAX.as_ref();
+    assert!(MAX.with(Function::is_instance_of::<Function>));
+    assert!(MAX.with(Function::is_instance_of::<Object>));
+    MAX.with(|max| {
+        let _: &Object = max.as_ref();
+    });
 }

crates/js-sys/tests/wasm/Object.rs

@@ -9,9 +9,9 @@ extern "C" {
     #[wasm_bindgen(method, setter, structural)]
     fn set_foo(this: &Foo42, val: JsValue);
 
-    #[wasm_bindgen(js_name = prototype, js_namespace = Object)]
+    #[wasm_bindgen(thread_local, js_name = prototype, js_namespace = Object)]
     static OBJECT_PROTOTYPE: JsValue;
-    #[wasm_bindgen(js_name = prototype, js_namespace = Array)]
+    #[wasm_bindgen(thread_local, js_name = prototype, js_namespace = Array)]
     static ARRAY_PROTOTYPE: JsValue;
 
     type DefinePropertyAttrs;
@@ -32,9 +32,9 @@ extern "C" {
     #[wasm_bindgen(constructor)]
     fn new() -> Foo;
 
-    #[wasm_bindgen(js_name = prototype, js_namespace = Foo)]
+    #[wasm_bindgen(thread_local, js_name = prototype, js_namespace = Foo)]
     static FOO_PROTOTYPE: Object;
-    #[wasm_bindgen(js_name = prototype, js_namespace = Bar)]
+    #[wasm_bindgen(thread_local, js_name = prototype, js_namespace = Bar)]
     static BAR_PROTOTYPE: Object;
 }
 
@@ -178,9 +178,9 @@ fn get_own_property_symbols() {
 #[wasm_bindgen_test]
 fn get_prototype_of() {
     let proto = JsValue::from(Object::get_prototype_of(&Object::new().into()));
-    assert_eq!(proto, *OBJECT_PROTOTYPE);
+    OBJECT_PROTOTYPE.with(|op| assert_eq!(proto, *op));
     let proto = JsValue::from(Object::get_prototype_of(&Array::new().into()));
-    assert_eq!(proto, *ARRAY_PROTOTYPE);
+    ARRAY_PROTOTYPE.with(|ap| assert_eq!(proto, *ap));
 }
 
 #[wasm_bindgen_test]
@@ -249,8 +249,8 @@ fn is_sealed() {
 #[wasm_bindgen_test]
 fn is_prototype_of() {
     let foo = JsValue::from(Foo::new());
-    assert!(FOO_PROTOTYPE.is_prototype_of(&foo));
-    assert!(!BAR_PROTOTYPE.is_prototype_of(&foo));
+    assert!(FOO_PROTOTYPE.with(|fp| fp.is_prototype_of(&foo)));
+    assert!(!BAR_PROTOTYPE.with(|bp| bp.is_prototype_of(&foo)));
 }
 
 #[wasm_bindgen_test]

crates/macro-support/src/parser.rs

@@ -93,6 +93,7 @@ macro_rules! attrgen {
             (typescript_type, TypeScriptType(Span, String, Span)),
             (getter_with_clone, GetterWithClone(Span)),
             (static_string, StaticString(Span)),
+            (thread_local, ThreadLocal(Span)),
 
             // For testing purposes only.
             (assert_no_shim, AssertNoShim(Span)),
@@ -753,6 +754,13 @@ impl<'a> ConvertToAst<(&ast::Program, BindgenAttrs, &'a Option<ast::ImportModule
             bail_span!(self.mutability, "cannot import mutable globals yet")
         }
 
+        if let Some(span) = opts.static_string() {
+            return Err(Diagnostic::span_error(
+                *span,
+                "static strings require a string literal",
+            ));
+        }
+
         let default_name = self.ident.to_string();
         let js_name = opts
             .js_name()
@@ -764,6 +772,8 @@ impl<'a> ConvertToAst<(&ast::Program, BindgenAttrs, &'a Option<ast::ImportModule
             self.ident,
             ShortHash((&js_name, module, &self.ident)),
         );
+        let thread_local = opts.thread_local().is_some();
+
         opts.check_used();
         Ok(ast::ImportKind::Static(ast::ImportStatic {
             ty: *self.ty,
@@ -772,6 +782,7 @@ impl<'a> ConvertToAst<(&ast::Program, BindgenAttrs, &'a Option<ast::ImportModule
             js_name,
             shim: Ident::new(&shim, Span::call_site()),
             wasm_bindgen: program.wasm_bindgen.clone(),
+            thread_local,
         }))
     }
 }
@@ -805,7 +816,14 @@ impl<'a> ConvertToAst<(&ast::Program, BindgenAttrs, &'a Option<ast::ImportModule
         if opts.static_string().is_none() {
             bail_span!(
                 self,
-                "statics strings require `#[wasm_bindgen(static_string)]`"
+                "static strings require `#[wasm_bindgen(static_string)]`"
+            )
+        }
+
+        if opts.thread_local().is_none() {
+            bail_span!(
+                self,
+                "static strings require `#[wasm_bindgen(thread_local)]`"
             )
         }
 

crates/macro/Cargo.toml

@@ -26,6 +26,7 @@ wasm-bindgen-macro-support = { path = "../macro-support", version = "=0.2.92" }
 quote = "1.0"
 
 [dev-dependencies]
+js-sys = { path = "../js-sys" }
 trybuild = "1.0"
 wasm-bindgen = { path = "../.." }
 wasm-bindgen-futures = { path = "../futures" }

crates/macro/ui-tests/invalid-items.rs

@@ -10,15 +10,26 @@ pub const fn foo2() {}
 struct Foo<T>(T);
 
 #[wasm_bindgen]
+#[rustfmt::skip]
 extern "C" {
     static mut FOO: u32;
 
+    #[wasm_bindgen(static_string)]
+    static FOO2: JsString;
+
+    #[wasm_bindgen(thread_local, static_string)]
+    static FOO3: JsString;
+
+    static FOO4: JsString = "test";
+
+    #[wasm_bindgen(static_string)]
+    static FOO5: JsString = "test";
+
     pub fn foo3(x: i32, ...);
 }
 
 #[wasm_bindgen]
-extern "system" {
-}
+extern "system" {}
 
 #[wasm_bindgen]
 pub fn foo4<T>() {}