fix(runtime-core): support for nested calls to runWithContext (vuejs#10261)

close vuejs#10260

Author: yangxiuxiu1115

packages/runtime-core/__tests__/apiCreateApp.spec.ts

@@ -123,6 +123,13 @@ describe('api: createApp', () => {
 
     expect(app.runWithContext(() => inject('foo'))).toBe(1)
 
+    expect(
+      app.runWithContext(() => {
+        app.runWithContext(() => {})
+        return inject('foo')
+      }),
+    ).toBe(1)
+
     // ensure the context is restored
     inject('foo')
     expect('inject() can only be used inside setup').toHaveBeenWarned()

packages/runtime-core/src/apiCreateApp.ts

@@ -387,11 +387,12 @@ export function createAppAPI<HostElement>(
       },
 
       runWithContext(fn) {
+        const lastApp = currentApp
         currentApp = app
         try {
           return fn()
         } finally {
-          currentApp = null
+          currentApp = lastApp
         }
       },
     })