Merge pull request #1410 from alexlapa/add-wasm-bindgen-skip-attr

Add wasm_bindgen(skip) attribute

crates/macro-support/src/parser.rs

@@ -51,6 +51,7 @@ macro_rules! attrgen {
             (variadic, Variadic(Span)),
             (typescript_custom_section, TypescriptCustomSection(Span)),
             (start, Start(Span)),
+            (skip, Skip(Span)),
         }
     };
 }
@@ -295,7 +296,7 @@ trait ConvertToAst<Ctx> {
 impl<'a> ConvertToAst<BindgenAttrs> for &'a mut syn::ItemStruct {
     type Target = ast::Struct;
 
-    fn convert(self, opts: BindgenAttrs) -> Result<Self::Target, Diagnostic> {
+    fn convert(self, attrs: BindgenAttrs) -> Result<Self::Target, Diagnostic> {
         if self.generics.params.len() > 0 {
             bail_span!(
                 self.generics,
@@ -304,7 +305,7 @@ impl<'a> ConvertToAst<BindgenAttrs> for &'a mut syn::ItemStruct {
             );
         }
         let mut fields = Vec::new();
-        let js_name = opts
+        let js_name = attrs
             .js_name()
             .map(|s| s.0.to_string())
             .unwrap_or(self.ident.to_string());
@@ -318,26 +319,33 @@ impl<'a> ConvertToAst<BindgenAttrs> for &'a mut syn::ItemStruct {
                     Some(n) => n,
                     None => continue,
                 };
+
+                let attrs = BindgenAttrs::find(&mut field.attrs)?;
+                assert_not_variadic(&attrs)?;
+                if attrs.skip().is_some() {
+                    attrs.check_used()?;
+                    continue
+                }
+
+                let comments = extract_doc_comments(&field.attrs);
                 let name_str = name.to_string();
                 let getter = shared::struct_field_get(&js_name, &name_str);
                 let setter = shared::struct_field_set(&js_name, &name_str);
-                let opts = BindgenAttrs::find(&mut field.attrs)?;
-                assert_not_variadic(&opts)?;
-                let comments = extract_doc_comments(&field.attrs);
+
                 fields.push(ast::StructField {
                     name: name.clone(),
                     struct_name: self.ident.clone(),
-                    readonly: opts.readonly().is_some(),
+                    readonly: attrs.readonly().is_some(),
                     ty: field.ty.clone(),
                     getter: Ident::new(&getter, Span::call_site()),
                     setter: Ident::new(&setter, Span::call_site()),
                     comments,
                 });
-                opts.check_used()?;
+                attrs.check_used()?;
             }
         }
         let comments: Vec<String> = extract_doc_comments(&self.attrs);
-        opts.check_used()?;
+        attrs.check_used()?;
         Ok(ast::Struct {
             rust_name: self.ident.clone(),
             js_name,

guide/src/SUMMARY.md

@@ -75,6 +75,7 @@
       - [`constructor`](./reference/attributes/on-rust-exports/constructor.md)
       - [`js_name = Blah`](./reference/attributes/on-rust-exports/js_name.md)
       - [`readonly`](./reference/attributes/on-rust-exports/readonly.md)
+      - [`skip`](./reference/attributes/on-rust-exports/skip.md)
       - [`start`](./reference/attributes/on-rust-exports/start.md)
       - [`typescript_custom_section`](./reference/attributes/on-rust-exports/typescript_custom_section.md)
 

guide/src/reference/attributes/on-rust-exports/skip.md

@@ -0,0 +1,46 @@
+# `skip`
+
+When attached to a `pub` struct field this indicates that field will not be exposed to JavaScript,
+and neither getter nor setter will be generated in ES6 class.
+
+```rust
+use wasm_bindgen::prelude::*;
+
+#[wasm_bindgen]
+pub struct Foo {
+    pub bar: u32,
+
+    #[wasm_bindgen(skip)]
+    pub baz: u32,
+}
+
+#[wasm_bindgen]
+impl Foo {
+    pub fn new() -> Self {
+        Foo {
+            bar: 1,
+            baz: 2
+        }
+    }
+}
+```
+
+Here the `bar` field will be both readable and writable from JS, but the
+`baz` field will be `undefined` in JS.
+
+```js
+import('./pkg/').then(rust => {
+    let foo = rust.Foo.new();
+    
+    // bar is accessible by getter
+    console.log(foo.bar);
+    // field marked with `skip` is undefined
+    console.log(foo.baz);      
+
+    // you can shadow it
+    foo.baz = 45;       
+    // so accessing by getter will return `45`
+    // but it won't affect real value in rust memory
+    console.log(foo.baz);
+});
+```

tests/wasm/classes.js

@@ -108,6 +108,8 @@ exports.js_public_fields = () => {
     assert.strictEqual(a.d, 0);
     a.d = 3.3;
     assert.strictEqual(a.d, 3);
+
+    assert.strictEqual(a.skipped, undefined);
 };
 
 exports.js_using_self = () => {

tests/wasm/classes.rs

@@ -274,6 +274,8 @@ pub struct PublicFields {
     pub b: f32,
     pub c: f64,
     pub d: i32,
+    #[wasm_bindgen(skip)]
+    pub skipped: u32
 }
 
 #[wasm_bindgen]