Support wildcard arguments in foreign functions (#351)

No real reason to not support them!

Closes #346

crates/backend/src/codegen.rs

@@ -573,6 +573,7 @@ impl ToTokens for ast::ImportFunction {
         let mut abi_argument_names = Vec::new();
         let mut abi_arguments = Vec::new();
         let mut arg_conversions = Vec::new();
+        let mut arguments = Vec::new();
         let ret_ident = Ident::new("_ret", Span::call_site());
 
         for (i, syn::ArgCaptured { pat, ty, .. }) in self.function.arguments.iter().enumerate() {
@@ -583,6 +584,9 @@ impl ToTokens for ast::ImportFunction {
                     subpat: None,
                     ..
                 }) => ident.clone(),
+                syn::Pat::Wild(_) => {
+                    syn::Ident::new(&format!("__genarg_{}", i), Span::call_site())
+                }
                 _ => panic!("unsupported pattern in foreign function"),
             };
 
@@ -593,6 +597,7 @@ impl ToTokens for ast::ImportFunction {
             let var = if i == 0 && is_method {
                 quote! { self }
             } else {
+                arguments.push(quote! { #name: #ty });
                 quote! { #name }
             };
             arg_conversions.push(quote! {
@@ -651,12 +656,7 @@ impl ToTokens for ast::ImportFunction {
         let rust_name = &self.rust_name;
         let import_name = &self.shim;
         let attrs = &self.function.rust_attrs;
-
+        let arguments = &arguments;
-        let arguments = if is_method {
-            &self.function.arguments[1..]
-        } else {
-            &self.function.arguments[..]
-        };
 
         let me = if is_method {
             quote! { &self, }

tests/all/imports.rs

@@ -490,6 +490,40 @@ fn versions() {
         .test();
 }
 
+#[test]
+fn underscore_pattern() {
+    project()
+        .debug(false)
+        .file("src/lib.rs", r#"
+            #![feature(proc_macro, wasm_custom_section, wasm_import_module)]
+
+            extern crate wasm_bindgen;
+
+            use wasm_bindgen::prelude::*;
+
+            #[wasm_bindgen(module = "./test")]
+            extern {
+                fn foo(_: u8);
+            }
+
+            #[wasm_bindgen]
+            pub fn run() {
+                foo(1);
+            }
+        "#)
+        .file("test.ts", r#"
+            import { run } from "./out";
+
+            export function foo(_a: number) {
+            }
+
+            export function test() {
+                run();
+            }
+        "#)
+        .test();
+}
+
 #[test]
 fn rust_keyword() {
     project()