fix symbol conflicts for post return (#602)

follow-up of #593

Author: xxchan

crates/rust/src/lib.rs

@@ -687,6 +687,7 @@ impl InterfaceGenerator<'_> {
             uwrite!(
                 macro_src,
                 "
+                    const _: () = {{
                     #[doc(hidden)]
                     #[export_name = \"cabi_post_{export_name}\"]
                     #[allow(non_snake_case)]
@@ -708,7 +709,8 @@ 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.post_return(func, &mut f);

crates/rust/tests/codegen.rs

@@ -184,9 +184,20 @@ mod symbol_does_not_conflict {
                 foo: func()
             }
 
+            interface bar1 {
+                bar: func() -> string
+            }
+
+            interface bar2 {
+                bar: func() -> string
+            }
+
+
             world foo {
                 export foo1
                 export foo2
+                export bar1
+                export bar2
             }
         ",
     });
@@ -201,5 +212,17 @@ mod symbol_does_not_conflict {
         fn foo() {}
     }
 
+    impl exports::my::inline::bar1::Bar1 for Component {
+        fn bar() -> String {
+            String::new()
+        }
+    }
+
+    impl exports::my::inline::bar2::Bar2 for Component {
+        fn bar() -> String {
+            String::new()
+        }
+    }
+
     export_foo!(Component);
 }