fail validation if callback missing for async export

crates/wit-component/src/validation.rs

@@ -1375,6 +1375,29 @@ impl ExportMap {
             bail!("cannot componentize module that exports multiple memories")
         }
 
+        // Every async-with-callback-lifted export must have a callback.
+        for (name, export) in &self.names {
+            match export {
+                Export::WorldFunc(_, _, AbiVariant::GuestExportAsync) => {
+                    if !matches!(
+                        self.names.get(&format!("[callback]{name}")),
+                        Some(Export::WorldFuncCallback(_))
+                    ) {
+                        bail!("missing callback for `{name}`");
+                    }
+                }
+                Export::InterfaceFunc(_, _, _, AbiVariant::GuestExportAsync) => {
+                    if !matches!(
+                        self.names.get(&format!("[callback]{name}")),
+                        Some(Export::InterfaceFuncCallback(_, _))
+                    ) {
+                        bail!("missing callback for `{name}`");
+                    }
+                }
+                _ => {}
+            }
+        }
+
         // All of `exports` must be exported and found within this module.
         for export in exports {
             let require_interface_func = |interface: InterfaceId, name: &str| -> Result<()> {

crates/wit-component/tests/components/error-async-export-missing-callback/error.txt

@@ -0,0 +1 @@
+failed to decode world from module: module was not valid: missing callback for `[async-lift]foo`

crates/wit-component/tests/components/error-async-export-missing-callback/module.wat

@@ -0,0 +1,6 @@
+(module
+  (func (export "[async-lift]foo") (param i32 i32) (result i32) unreachable)
+  (func (export "[async-lift]foo:foo/bar#foo") (param i32 i32) (result i32) unreachable)
+  (memory (export "memory") 1)
+  (func (export "cabi_realloc") (param i32 i32 i32 i32) (result i32) unreachable)
+)

crates/wit-component/tests/components/error-async-export-missing-callback/module.wit

@@ -0,0 +1,10 @@
+package foo:foo;
+
+interface bar {
+  foo: func(s: string) -> string;
+}
+
+world module {
+  export bar;
+  export foo: func(s: string) -> string;
+}