Add codegen to make test work.

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

@@ -1614,7 +1614,6 @@ impl<'a> Context<'a> {
     }
 
     fn global(&mut self, s: &str) {
-        let s = s;
         let s = s.trim();
 
         // Ensure a blank line between adjacent items, and ensure everything is
@@ -1941,6 +1940,7 @@ impl<'a, 'b> SubContext<'a, 'b> {
 
         let js = Rust2Js::new(self.cx)
             .catch(import.catch)
+            .variadic(import.variadic)
             .process(descriptor.unwrap_function())?
             .finish(&target);
         self.cx.export(&import.shim, &js, None);

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

@@ -36,6 +36,9 @@ pub struct Rust2Js<'a, 'b: 'a> {
 
     /// Whether or not we're catching JS exceptions
     catch: bool,
+
+    /// Whether or not the last argument is a slice representing variadic arguments.
+    variadic: bool,
 }
 
 impl<'a, 'b> Rust2Js<'a, 'b> {
@@ -50,6 +53,7 @@ impl<'a, 'b> Rust2Js<'a, 'b> {
             arg_idx: 0,
             ret_expr: String::new(),
             catch: false,
+            variadic: false,
         }
     }
 
@@ -62,6 +66,15 @@ impl<'a, 'b> Rust2Js<'a, 'b> {
         self
     }
 
+    pub fn variadic(&mut self, variadic: bool) -> &mut Self {
+        if variadic {
+            self.cx.expose_uint32_memory();
+            self.cx.expose_add_heap_object();
+        }
+        self.variadic = variadic;
+        self
+    }
+
     /// 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> {
@@ -72,6 +85,7 @@ impl<'a, 'b> Rust2Js<'a, 'b> {
         Ok(self)
     }
 
+    /// Get a generated name for an argument.
     fn shim_argument(&mut self) -> String {
         let s = format!("arg{}", self.arg_idx);
         self.arg_idx += 1;
@@ -516,6 +530,7 @@ impl<'a, 'b> Rust2Js<'a, 'b> {
     }
 
     pub fn finish(&self, invoc: &str) -> String {
+        use std::fmt::Write;
         let mut ret = String::new();
         ret.push_str("function(");
         ret.push_str(&self.shim_arguments.join(", "));
@@ -528,10 +543,31 @@ impl<'a, 'b> Rust2Js<'a, 'b> {
         ret.push_str(") {\n");
         ret.push_str(&self.prelude);
 
-        let mut invoc = self.ret_expr.replace(
-            "JS",
-            &format!("{}({})", invoc, self.js_arguments.join(", ")),
-        );
+        let mut invoc = if self.variadic {
+            if self.js_arguments.is_empty() {
+                unreachable!("the last argument of a variadic must be a slice");
+            }
+            let last_arg = self.js_arguments.len() - 1; // check implies > 0
+            // The variadic part of the arguments could be passed as as a typed array in
+            // javascript, so we cannot just do `.concat(..)`, as this seems to convert the
+            // contents to strings (javascript is very strange).
+            write!(ret, "\
+                let args = [{}];\n\
+                {}.forEach(extra_arg => args.push(extra_arg));\n\
+                ",
+                self.js_arguments[..last_arg].join(", "),
+                self.js_arguments[last_arg]
+            ).unwrap();
+            self.ret_expr.replace(
+                "JS",
+                &format!("{}.apply(this, args)", invoc),
+            )
+        } else {
+            self.ret_expr.replace(
+                "JS",
+                &format!("{}({})", invoc, self.js_arguments.join(", ")),
+            )
+        };
         if self.catch {
             let catch = "\
                          const view = getUint32Memory();\n\