Preserve argument names

crates/backend/src/encode.rs

@@ -165,7 +165,22 @@ fn shared_export<'a>(export: &'a ast::Export, intern: &'a Interner) -> Export<'a
 }
 
 fn shared_function<'a>(func: &'a ast::Function, _intern: &'a Interner) -> Function<'a> {
-    Function { name: &func.name }
+    let arg_names = func
+        .arguments
+        .iter()
+        .enumerate()
+        .map(|(idx, arg)| {
+            if let syn::Pat::Ident(ref x) = arg.pat {
+                x.ident.to_string()
+            } else {
+                format!("arg{}", idx)
+            }
+        })
+        .collect::<Vec<_>>();
+    Function {
+        name: &func.name,
+        arg_names,
+    }
 }
 
 fn shared_enum<'a>(e: &'a ast::Enum, intern: &'a Interner) -> Enum<'a> {
@@ -364,6 +379,12 @@ impl<'a> Encode for &'a str {
     }
 }
 
+impl<'a> Encode for String {
+    fn encode(&self, dst: &mut Encoder) {
+        self.as_bytes().encode(dst);
+    }
+}
+
 impl<T: Encode> Encode for Vec<T> {
     fn encode(&self, dst: &mut Encoder) {
         self.len().encode(dst);

crates/cli-support/src/decode.rs

@@ -46,6 +46,15 @@ impl<'src> Decode<'src> for &'src str {
     }
 }
 
+impl<'src> Decode<'src> for String {
+    fn decode(data: &mut &'src [u8]) -> String {
+        let n = u32::decode(data);
+        let (a, b) = data.split_at(n as usize);
+        *data = b;
+        String::from_utf8(a.to_vec()).unwrap()
+    }
+}
+
 impl<'src, T: Decode<'src>> Decode<'src> for Vec<T> {
     fn decode(data: &mut &'src [u8]) -> Self {
         let n = u32::decode(data);

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

@@ -193,7 +193,7 @@ impl ClosureDescriptors {
                     builder.rust_argument("this.a").rust_argument("b");
                 }
                 builder.finally("if (this.cnt-- == 1) d(this.a, b);");
-                builder.process(&closure.function)?.finish(
+                builder.process(&closure.function, None)?.finish(
                     "function",
                     "f",
                     ExportedShim::TableElement(&mut shim),

crates/cli-support/src/js/js2rust.rs

@@ -75,9 +75,22 @@ impl<'a, 'b> Js2Rust<'a, 'b> {
 
     /// Generates all bindings necessary for the signature in `Function`,
     /// creating necessary argument conversions and return value processing.
-    pub fn process(&mut self, function: &Function) -> Result<&mut Self, Error> {
-        for arg in function.arguments.iter() {
-            self.argument(arg)?;
+    pub fn process<'c, I>(
+        &mut self,
+        function: &Function,
+        opt_arg_names: I,
+    ) -> Result<&mut Self, Error>
+    where
+        I: Into<Option<&'c Vec<String>>>,
+    {
+        if let Some(arg_names) = opt_arg_names.into() {
+            for (arg, arg_name) in function.arguments.iter().zip(arg_names) {
+                self.argument(arg, arg_name.clone())?;
+            }
+        } else {
+            for arg in function.arguments.iter() {
+                self.argument(arg, None)?;
+            }
         }
         self.ret(&function.ret)?;
         Ok(self)
@@ -138,15 +151,22 @@ impl<'a, 'b> Js2Rust<'a, 'b> {
         self
     }
 
-    fn abi_arg(&mut self) -> String {
-        let s = format!("arg{}", self.arg_idx);
+    fn abi_arg(&mut self, opt_arg_name: Option<String>) -> String {
+        let ret = if let Some(x) = opt_arg_name {
+            x
+        } else {
+            format!("arg{}", self.arg_idx)
+        };
         self.arg_idx += 1;
-        s
+        ret
     }
 
-    pub fn argument(&mut self, arg: &Descriptor) -> Result<&mut Self, Error> {
+    pub fn argument<I>(&mut self, arg: &Descriptor, opt_arg_name: I) -> Result<&mut Self, Error>
+    where
+        I: Into<Option<String>>,
+    {
         let i = self.arg_idx;
-        let name = self.abi_arg();
+        let name = self.abi_arg(opt_arg_name.into());
 
         let (arg, optional) = match arg {
             Descriptor::Option(t) => (&**t, true),

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

@@ -2498,7 +2498,7 @@ impl<'a, 'b> SubContext<'a, 'b> {
         }
 
         let (js, ts, js_doc) = Js2Rust::new(&export.function.name, self.cx)
-            .process(descriptor.unwrap_function())?
+            .process(descriptor.unwrap_function(), &export.function.arg_names)?
             .finish(
                 "function",
                 &format!("wasm.{}", export.function.name),
@@ -2554,7 +2554,7 @@ impl<'a, 'b> SubContext<'a, 'b> {
             } else {
                 None
             })
-            .process(descriptor.unwrap_function())?
+            .process(descriptor.unwrap_function(), &export.function.arg_names)?
             .finish(
                 "",
                 &format!("wasm.{}", wasm_name),
@@ -2772,7 +2772,7 @@ impl<'a, 'b> SubContext<'a, 'b> {
                 let setter = ExportedShim::Named(&wasm_setter);
                 let mut cx = Js2Rust::new(&field.name, self.cx);
                 cx.method(true, false)
-                    .argument(&descriptor)?
+                    .argument(&descriptor, None)?
                     .ret(&Descriptor::Unit)?;
                 ts_dst.push_str(&format!(
                     "\n  {}{}: {};",

crates/cli-support/src/js/rust2js.rs

@@ -285,7 +285,7 @@ impl<'a, 'b> Rust2Js<'a, 'b> {
                 } else {
                     builder.rust_argument("this.a");
                 }
-                builder.rust_argument("this.b").process(f)?.finish(
+                builder.rust_argument("this.b").process(f, None)?.finish(
                     "function",
                     "this.f",
                     ExportedShim::TableElement(&mut shim),

crates/shared/src/lib.rs

@@ -106,6 +106,7 @@ macro_rules! shared_api {
         }
 
         struct Function<'a> {
+            arg_names: Vec<String>,
             name: &'a str,
         }
 

tests/wasm/arg_names.js

@@ -0,0 +1,16 @@
+const wasm = require('wasm-bindgen-test.js');
+const assert = require('assert');
+
+const ARGUMENT_NAMES = /([^\s,]+)/g;
+const STRIP_COMMENTS = /((\/\/.*$)|(\/\*[\s\S]*?\*\/))/mg;
+
+// https://stackoverflow.com/q/1007981/210304
+function getArgNames(func) {
+    let fnStr = func.toString().replace(STRIP_COMMENTS, '');
+    let result = fnStr.slice(fnStr.indexOf('(')+1, fnStr.indexOf(')')).match(ARGUMENT_NAMES);
+    return result === null ? [] : result;
+}
+
+exports.js_arg_names = () => {
+    assert.deepEqual(getArgNames(wasm.fn_with_many_args), ['_a', '_b', '_c', '_d']);
+};

tests/wasm/arg_names.rs

@@ -0,0 +1,15 @@
+use wasm_bindgen::prelude::*;
+use wasm_bindgen_test::*;
+
+#[wasm_bindgen(module = "tests/wasm/arg_names.js")]
+extern "C" {
+    fn js_arg_names();
+}
+
+#[wasm_bindgen]
+pub fn fn_with_many_args(_a: i32, _b: i32, _c: i32, _d: i32) {}
+
+#[wasm_bindgen_test]
+fn rust_arg_names() {
+    js_arg_names();
+}

tests/wasm/main.rs

@@ -13,6 +13,7 @@ extern crate serde_derive;
 use wasm_bindgen::prelude::*;
 
 pub mod api;
+pub mod arg_names;
 pub mod char;
 pub mod classes;
 pub mod closures;