Avoid errors if vendor-prefixed APIs do not exist

Avoid errors in the generated vendor-prefix code if neither the
standard API nor the vendor-prefixed API exists. Instead, fall back
to undefined, which will give the Rust module a chance to run and
handle the error when it tries to use the API.

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

@@ -2095,18 +2095,18 @@ impl<'a> Context<'a> {
  self.imports_post.push_str(";\n");
 
  fn switch(dst: &mut String, name: &str, prefix: &str, left: &[String]) {
- if left.len() == 0 {
- dst.push_str(prefix);
- return dst.push_str(name);
- }
  dst.push_str("(typeof ");
  dst.push_str(prefix);
  dst.push_str(name);
  dst.push_str(" !== 'undefined' ? ");
  dst.push_str(prefix);
  dst.push_str(name);
  dst.push_str(" : ");
- switch(dst, name, &left[0], &left[1..]);
+ if left.len() > 0 {
+ switch(dst, name, &left[0], &left[1..]);
+ } else {
+ dst.push_str("undefined");
+ }
  dst.push_str(")");
  }
  format!("l{}", name)

tests/wasm/vendor_prefix.rs

@@ -28,6 +28,13 @@ extern "C" {
  fn new() -> MySpecialApi3;
  #[wasm_bindgen(method)]
  fn foo(this: &MySpecialApi3) -> u32;
+
+ // This API does not exist at all;
+ // test that Rust gets a chance to catch the error (#2437)
+ #[wasm_bindgen(vendor_prefix = a, vendor_prefix = b)]
+ type MyMissingApi;
+ #[wasm_bindgen(constructor, catch)]
+ fn new() -> Result<MyMissingApi, JsValue>;
 }
 
 #[wasm_bindgen_test]
@@ -37,4 +44,5 @@ pub fn polyfill_works() {
  assert_eq!(MySpecialApi::new().foo(), 123);
  assert_eq!(MySpecialApi2::new().foo(), 124);
  assert_eq!(MySpecialApi3::new().foo(), 125);
+ assert!(MyMissingApi::new().is_err());
 }