Fix symbol conflicts in exported Rust functions (#593)

Closes #592

Author: alexcrichton

crates/rust/src/lib.rs

@@ -566,6 +566,7 @@ impl InterfaceGenerator<'_> {
         uwrite!(
             macro_src,
             "
+            const _: () = {{
                 #[doc(hidden)]
                 #[export_name = \"{export_name}\"]
                 #[allow(non_snake_case)]
@@ -647,7 +648,8 @@ impl InterfaceGenerator<'_> {
         for param in params.iter() {
             uwrite!(macro_src, "{param},");
         }
-        uwriteln!(macro_src, ")\n}}");
+        uwriteln!(macro_src, ")\n}}"); // close function call and function
+        uwriteln!(macro_src, "\n}};"); // close `const _: () = { ...`
 
         let mut f = FunctionBindgen::new(self, params);
         f.gen.resolve.call(

crates/rust/tests/codegen.rs

@@ -168,3 +168,36 @@ mod skip {
 
     export_baz!(Component);
 }
+
+mod symbol_does_not_conflict {
+    wit_bindgen::generate!({
+        inline: "
+            package my:inline
+
+            interface foo1 {
+                foo: func()
+            }
+
+            interface foo2 {
+                foo: func()
+            }
+
+            world foo {
+                export foo1
+                export foo2
+            }
+        ",
+    });
+
+    struct Component;
+
+    impl exports::my::inline::foo1::Foo1 for Component {
+        fn foo() {}
+    }
+
+    impl exports::my::inline::foo2::Foo2 for Component {
+        fn foo() {}
+    }
+
+    export_foo!(Component);
+}