fix: block.super with strictVariables, #806 (#807)

src/drop/block-drop.ts

@@ -1,9 +1,10 @@
+import { Emitter, SimpleEmitter } from '../emitters'
 import { Drop } from './drop'
 
 export class BlockDrop extends Drop {
   constructor (
     // the block render from layout template
-    private superBlockRender: () => Iterable<any> = () => ''
+    private superBlockRender: (emitter: Emitter) => IterableIterator<unknown> | string = () => ''
   ) {
     super()
   }
@@ -11,7 +12,9 @@ export class BlockDrop extends Drop {
    * Provide parent access in child block by
    * {{ block.super }}
    */
-  public super () {
-    return this.superBlockRender()
+  public * super (): IterableIterator<unknown> {
+    const emitter = new SimpleEmitter()
+    yield this.superBlockRender(emitter)
+    return emitter.buffer
   }
 }