Add exporting Rust functions as variadic JS functions (#2954)

* add variadic argument into function structures

* bind variadic function last argument

* comment variadic assertions

* add variadic functions tests

* fix variadic var name

* add new schema file hash in the shared crate

* add variadic param in JS doc

* remove assert_not_variadic references

* add variadic TS tests

* update variadic docs

Author: joaofreires

crates/backend/src/ast.rs

@@ -303,6 +303,8 @@ pub struct Function {
     pub r#async: bool,
     /// Whether to generate a typescript definition for this function
     pub generate_typescript: bool,
+    /// Whether this is a function with a variadict parameter
+    pub variadic: bool,
 }
 
 /// Information about a Struct being exported

crates/backend/src/encode.rs

@@ -212,6 +212,7 @@ fn shared_function<'a>(func: &'a ast::Function, _intern: &'a Interner) -> Functi
         asyncness: func.r#async,
         name: &func.name,
         generate_typescript: func.generate_typescript,
+        variadic: func.variadic,
     }
 }
 

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

@@ -102,6 +102,7 @@ impl<'a, 'b> Builder<'a, 'b> {
         instructions: &[InstructionData],
         explicit_arg_names: &Option<Vec<String>>,
         asyncness: bool,
+        variadic: bool,
     ) -> Result<JsFunction, Error> {
         if self
             .cx
@@ -193,7 +194,17 @@ impl<'a, 'b> Builder<'a, 'b> {
 
         let mut code = String::new();
         code.push_str("(");
-        code.push_str(&function_args.join(", "));
+        if variadic {
+            if let Some((last, non_variadic_args)) = function_args.split_last() {
+                code.push_str(&non_variadic_args.join(", "));
+                if non_variadic_args.len() > 0 {
+                    code.push_str(", ");
+                }
+                code.push_str((String::from("...") + last).as_str())
+            }
+        } else {
+            code.push_str(&function_args.join(", "));
+        }
         code.push_str(") {\n");
 
         let mut call = js.prelude;
@@ -227,8 +238,9 @@ impl<'a, 'b> Builder<'a, 'b> {
             &adapter.inner_results,
             &mut might_be_optional_field,
             asyncness,
+            variadic,
         );
-        let js_doc = self.js_doc_comments(&function_args, &arg_tys, &ts_ret_ty);
+        let js_doc = self.js_doc_comments(&function_args, &arg_tys, &ts_ret_ty, variadic);
 
         Ok(JsFunction {
             code,
@@ -254,6 +266,7 @@ impl<'a, 'b> Builder<'a, 'b> {
         result_tys: &[AdapterType],
         might_be_optional_field: &mut bool,
         asyncness: bool,
+        variadic: bool,
     ) -> (String, Vec<String>, Option<String>) {
         // Build up the typescript signature as well
         let mut omittable = true;
@@ -284,7 +297,19 @@ impl<'a, 'b> Builder<'a, 'b> {
         }
         ts_args.reverse();
         ts_arg_tys.reverse();
-        let mut ts = format!("({})", ts_args.join(", "));
+        let mut ts = String::from("(");
+        if variadic {
+            if let Some((last, non_variadic_args)) = ts_args.split_last() {
+                ts.push_str(&non_variadic_args.join(", "));
+                if non_variadic_args.len() > 0 {
+                    ts.push_str(", ");
+                }
+                ts.push_str((String::from("...") + last).as_str())
+            }
+        } else {
+            ts.push_str(&format!("{}", ts_args.join(", ")));
+        };
+        ts.push_str(")");
 
         // If this function is an optional field's setter, it should have only
         // one arg, and omittable should be `true`.
@@ -318,15 +343,27 @@ impl<'a, 'b> Builder<'a, 'b> {
         arg_names: &[String],
         arg_tys: &[&AdapterType],
         ts_ret: &Option<String>,
+        variadic: bool,
     ) -> String {
         let mut ret = String::new();
-        for (name, ty) in arg_names.iter().zip(arg_tys) {
+        let (variadic_arg, fn_arg_names) = match arg_names.split_last() {
+            Some((last, args)) if variadic => (Some(last), args),
+            _ => (None, arg_names),
+        };
+        for (name, ty) in fn_arg_names.iter().zip(arg_tys) {
             ret.push_str("@param {");
             adapter2ts(ty, &mut ret);
             ret.push_str("} ");
             ret.push_str(name);
             ret.push_str("\n");
         }
+        if let (Some(name), Some(ty)) = (variadic_arg, arg_tys.last()) {
+            ret.push_str("@param {...");
+            adapter2ts(ty, &mut ret);
+            ret.push_str("} ");
+            ret.push_str(name);
+            ret.push_str("\n");
+        }
         if let Some(ts) = ts_ret {
             if ts != "void" {
                 ret.push_str(&format!("@returns {{{}}}", ts));

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

@@ -2511,10 +2511,12 @@ impl<'a> Context<'a> {
         builder.catch(catch);
         let mut arg_names = &None;
         let mut asyncness = false;
+        let mut variadic = false;
         match kind {
             Kind::Export(export) => {
                 arg_names = &export.arg_names;
                 asyncness = export.asyncness;
+                variadic = export.variadic;
                 match &export.kind {
                     AuxExportKind::Function(_) => {}
                     AuxExportKind::StaticFunction { .. } => {}
@@ -2539,7 +2541,7 @@ impl<'a> Context<'a> {
             catch,
             log_error,
         } = builder
-            .process(&adapter, instrs, arg_names, asyncness)
+            .process(&adapter, instrs, arg_names, asyncness, variadic)
             .with_context(|| match kind {
                 Kind::Export(e) => format!("failed to generate bindings for `{}`", e.debug_name),
                 Kind::Import(i) => {

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

@@ -464,6 +464,7 @@ impl<'a> Context<'a> {
                 asyncness: export.function.asyncness,
                 kind,
                 generate_typescript: export.function.generate_typescript,
+                variadic: export.function.variadic,
             },
         );
         Ok(())
@@ -822,6 +823,7 @@ impl<'a> Context<'a> {
                         consumed: false,
                     },
                     generate_typescript: field.generate_typescript,
+                    variadic: false,
                 },
             );
 
@@ -851,6 +853,7 @@ impl<'a> Context<'a> {
                         consumed: false,
                     },
                     generate_typescript: field.generate_typescript,
+                    variadic: false,
                 },
             );
         }
@@ -1085,6 +1088,7 @@ impl<'a> Context<'a> {
                 asyncness: false,
                 kind,
                 generate_typescript: true,
+                variadic: false,
             };
             assert!(self.aux.export_map.insert(id, export).is_none());
         }

crates/cli-support/src/wit/nonstandard.rs

@@ -79,6 +79,8 @@ pub struct AuxExport {
     pub kind: AuxExportKind,
     /// Whether typescript bindings should be generated for this export.
     pub generate_typescript: bool,
+    /// Whether typescript bindings should be generated for this export.
+    pub variadic: bool,
 }
 
 /// All possible kinds of exports from a wasm module.

crates/macro-support/src/parser.rs

@@ -411,7 +411,6 @@ impl<'a> ConvertToAst<BindgenAttrs> for &'a mut syn::ItemStruct {
             };
 
             let attrs = BindgenAttrs::find(&mut field.attrs)?;
-            assert_not_variadic(&attrs)?;
             if attrs.skip().is_some() {
                 attrs.check_used()?;
                 continue;
@@ -627,7 +626,6 @@ impl ConvertToAst<BindgenAttrs> for syn::ForeignItemType {
     type Target = ast::ImportKind;
 
     fn convert(self, attrs: BindgenAttrs) -> Result<Self::Target, Diagnostic> {
-        assert_not_variadic(&attrs)?;
         let js_name = attrs
             .js_name()
             .map(|s| s.0)
@@ -678,7 +676,7 @@ impl<'a> ConvertToAst<(BindgenAttrs, &'a ast::ImportModule)> for syn::ForeignIte
         if self.mutability.is_some() {
             bail_span!(self.mutability, "cannot import mutable globals yet")
         }
-        assert_not_variadic(&opts)?;
+
         let default_name = self.ident.to_string();
         let js_name = opts
             .js_name()
@@ -718,7 +716,6 @@ impl ConvertToAst<BindgenAttrs> for syn::ItemFn {
         if self.sig.unsafety.is_some() {
             bail_span!(self.sig.unsafety, "can only #[wasm_bindgen] safe functions");
         }
-        assert_not_variadic(&attrs)?;
 
         let ret = function_from_decl(
             &self.sig.ident,
@@ -859,6 +856,7 @@ fn function_from_decl(
             rust_vis: vis,
             r#async: sig.asyncness.is_some(),
             generate_typescript: opts.skip_typescript().is_none(),
+            variadic: opts.variadic().is_some(),
         },
         method_self,
     ))
@@ -1558,16 +1556,6 @@ fn assert_no_lifetimes(sig: &syn::Signature) -> Result<(), Diagnostic> {
     Diagnostic::from_vec(walk.diagnostics)
 }
 
-/// This method always fails if the BindgenAttrs contain variadic
-fn assert_not_variadic(attrs: &BindgenAttrs) -> Result<(), Diagnostic> {
-    if let Some(span) = attrs.variadic() {
-        let msg = "the `variadic` attribute can only be applied to imported \
-                   (`extern`) functions";
-        return Err(Diagnostic::span_error(*span, msg));
-    }
-    Ok(())
-}
-
 /// Extracts the last ident from the path
 fn extract_path_ident(path: &syn::Path) -> Result<Ident, Diagnostic> {
     for segment in path.segments.iter() {

crates/shared/src/lib.rs

@@ -118,6 +118,7 @@ macro_rules! shared_api {
             asyncness: bool,
             name: &'a str,
             generate_typescript: bool,
+            variadic: bool,
         }
 
         struct Struct<'a> {

crates/shared/src/schema_hash_approval.rs

@@ -8,7 +8,7 @@
 // If the schema in this library has changed then:
 //  1. Bump the version in `crates/shared/Cargo.toml`
 //  2. Change the `SCHEMA_VERSION` in this library to this new Cargo.toml version
-const APPROVED_SCHEMA_FILE_HASH: &'static str = "3468290064813615840";
+const APPROVED_SCHEMA_FILE_HASH: &'static str = "16056751188521403565";
 
 #[test]
 fn schema_version() {

crates/typescript-tests/src/simple_fn.rs

@@ -7,3 +7,8 @@ pub fn greet(_: &str) {}
 pub fn take_and_return_bool(_: bool) -> bool {
     true
 }
+
+#[wasm_bindgen(variadic)]
+pub fn variadic_function(arr: &JsValue) -> JsValue {
+    arr.into()
+}

crates/typescript-tests/src/simple_fn.ts

@@ -4,3 +4,5 @@ import * as wasm from '../pkg/typescript_tests_bg.wasm';
 const wbg_greet: (a: string) => void = wbg.greet;
 const wasm_greet: (a: number, b: number) => void = wasm.greet;
 const take_and_return_bool: (a: boolean) => boolean = wbg.take_and_return_bool;
+const wbg_variadic_function: (...arr: any) => any = wbg.variadic_function;
+const wasm_variadic_function: (arr: number) => number = wasm.variadic_function;

guide/src/reference/attributes/on-js-imports/variadic.md

@@ -36,3 +36,18 @@ extern "C" {
 
 when we call this function, the last argument will be expanded as the javascript expects.
 
+
+To export a rust function to javascript with a variadic argument, we will use the same bindgen variadic attribute and assume that the last argument will be the variadic array. For example the following rust function:
+
+```rust
+#[wasm_bindgen(variadic)]
+pub  fn  variadic_function(arr: &JsValue) -> JsValue {
+	arr.into()
+}
+```
+
+will generate the following TS interface
+
+```ts
+export  function  variadic_function(...arr:  any):  any;
+```

tests/wasm/api.js

@@ -20,24 +20,36 @@ exports.js_works = () => {
     assert.strictEqual(wasm.api_get_false(), false);
     wasm.api_test_bool(true, false, 1.0);
 
-    assert.strictEqual(typeof(wasm.api_mk_symbol()), 'symbol');
-    assert.strictEqual(typeof(wasm.api_mk_symbol2('a')), 'symbol');
+    assert.strictEqual(typeof (wasm.api_mk_symbol()), 'symbol');
+    assert.strictEqual(typeof (wasm.api_mk_symbol2('a')), 'symbol');
     assert.strictEqual(Symbol.keyFor(wasm.api_mk_symbol()), undefined);
     assert.strictEqual(Symbol.keyFor(wasm.api_mk_symbol2('b')), undefined);
 
     wasm.api_assert_symbols(Symbol(), 'a');
     wasm.api_acquire_string('foo', null);
     assert.strictEqual(wasm.api_acquire_string2(''), '');
     assert.strictEqual(wasm.api_acquire_string2('a'), 'a');
+
+    let arr = [1, 2, 3, 4, {}, ['a', 'b', 'c']]
+    wasm.api_completely_variadic(...arr).forEach((element, index) => {
+        assert.strictEqual(element, arr[index]);
+    });
+    assert.strictEqual(
+        wasm.api_completely_variadic().length,
+        0
+    );
+    wasm.api_variadic_with_prefixed_params([], {}, ...arr).forEach((element, index) => {
+        assert.strictEqual(element, arr[index]);
+    });
 };
 
 exports.js_eq_works = () => {
     assert.strictEqual(wasm.eq_test('a', 'a'), true);
     assert.strictEqual(wasm.eq_test('a', 'b'), false);
     assert.strictEqual(wasm.eq_test(NaN, NaN), false);
-    assert.strictEqual(wasm.eq_test({a: 'a'}, {a: 'a'}), false);
+    assert.strictEqual(wasm.eq_test({ a: 'a' }, { a: 'a' }), false);
     assert.strictEqual(wasm.eq_test1(NaN), false);
-    let x = {a: 'a'};
+    let x = { a: 'a' };
     assert.strictEqual(wasm.eq_test(x, x), true);
     assert.strictEqual(wasm.eq_test1(x), true);
 };
@@ -48,16 +60,16 @@ exports.debug_values = () => ([
     0,
     1.0,
     true,
-    [1,2,3],
+    [1, 2, 3],
     "string",
-    {test: "object"},
+    { test: "object" },
     [1.0, [2.0, 3.0]],
     () => (null),
     new Set(),
 ]);
 
 exports.assert_function_table = (x, i) => {
-  const rawWasm = require('wasm-bindgen-test.js').__wasm;
-  assert.ok(x instanceof WebAssembly.Table);
-  assert.strictEqual(x.get(i), rawWasm.function_table_lookup);
+    const rawWasm = require('wasm-bindgen-test.js').__wasm;
+    assert.ok(x instanceof WebAssembly.Table);
+    assert.strictEqual(x.get(i), rawWasm.function_table_lookup);
 };

tests/wasm/api.rs

@@ -126,6 +126,20 @@ pub fn eq_test1(a: &JsValue) -> bool {
     a == a
 }
 
+#[wasm_bindgen(variadic)]
+pub fn api_completely_variadic(args: &JsValue) -> JsValue {
+    args.into()
+}
+
+#[wasm_bindgen(variadic)]
+pub fn api_variadic_with_prefixed_params(
+    first: &JsValue,
+    second: &JsValue,
+    args: &JsValue,
+) -> JsValue {
+    args.into()
+}
+
 #[wasm_bindgen_test]
 fn null_keeps_working() {
     assert_null(JsValue::null());