web-sys: Add support for Global-scope methods

This commit adds further support for the `Global` attribute to not only emit
structural accessors but also emit functions that don't take `&self`. All
methods on a `[Global]` interface will not require `&self` and will call
functions and/or access properties on the global scope.

This should enable things like:

    Window::location() // returns `Location`
    Window::fetch(...) // invokes the `fetch` function

Closes #659

crates/webidl-tests/global.js

@@ -0,0 +1,4 @@
+global.global_no_args = () => 3;
+global.global_with_args = (a, b) => a + b;
+global.global_attribute = 'x';
+

crates/webidl-tests/global.rs

@@ -0,0 +1,12 @@
+use wasm_bindgen_test::*;
+
+include!(concat!(env!("OUT_DIR"), "/global.rs"));
+
+#[wasm_bindgen_test]
+fn works() {
+    assert_eq!(Global::global_no_args(), 3);
+    assert_eq!(Global::global_with_args("a", "b"), "ab");
+    assert_eq!(Global::global_attribute(), "x");
+    Global::set_global_attribute("y");
+    assert_eq!(Global::global_attribute(), "y");
+}

crates/webidl-tests/global.webidl

@@ -0,0 +1,6 @@
+[Global=x]
+interface Global {
+  unsigned long global_no_args();
+  DOMString global_with_args(DOMString a, DOMString b);
+  attribute DOMString global_attribute;
+};

crates/webidl-tests/main.rs

@@ -10,3 +10,4 @@ pub mod namespace;
 pub mod simple;
 pub mod throws;
 pub mod dictionary;
+pub mod global;

crates/webidl-tests/simple.js

@@ -87,11 +87,7 @@ global.Unforgeable = class Unforgeable {
   }
 };
 
-global.GlobalMethod = class GlobalMethod {
-  constructor() {
-    this.m = () => 123;
-  }
-};
+global.m = () => 123;
 
 global.Indexing = function () {
   return new Proxy({}, {

crates/webidl-tests/simple.rs

@@ -64,8 +64,7 @@ fn nullable_method() {
 
 #[wasm_bindgen_test]
 fn global_method() {
-    let f = GlobalMethod::new().unwrap();
-    assert_eq!(f.m(), 123);
+    assert_eq!(GlobalMethod::m(), 123);
 }
 
 #[wasm_bindgen_test]