dx(suspense): warn when using async setup when not inside a Suspense boundary (#5565)

close #3649

packages/runtime-core/src/component.ts

@@ -654,7 +654,6 @@ function setupStatefulComponent(
 
     if (isPromise(setupResult)) {
       setupResult.then(unsetCurrentInstance, unsetCurrentInstance)
-
       if (isSSR) {
         // return the promise so server-renderer can wait on it
         return setupResult
@@ -668,6 +667,15 @@ function setupStatefulComponent(
         // async setup returned Promise.
         // bail here and wait for re-entry.
         instance.asyncDep = setupResult
+        if (__DEV__ && !instance.suspense) {
+          const name = Component.name ?? 'Anonymous'
+          warn(
+            `Component <${name}>: setup function returned a promise, but no ` +
+              `<Suspense> boundary was found in the parent component tree. ` +
+              `A component with async setup() must be nested in a <Suspense> ` +
+              `in order to be rendered.`
+          )
+        }
       } else if (__DEV__) {
         warn(
           `setup() returned a Promise, but the version of Vue you are using ` +