[BUGFIX lts] ensure deserializeQueryParam is called for lazy routes

packages/@ember/-internals/glimmer/tests/integration/application/engine-test.js

@@ -974,5 +974,64 @@ moduleFor(
           assert.equal(error.message, 'Whoops! Something went wrong...');
         });
     }
+
+    ['@test visit() with `shouldRender: true` queryParams are properly deserialized for lazy routes'](
+      assert
+    ) {
+      assert.expect(2);
+
+      let hooks = [];
+
+      this.setupAppAndRoutableEngine(hooks);
+
+      this.add(
+        'engine:blog',
+        Engine.extend({
+          Resolver: ModuleBasedTestResolver,
+
+          init() {
+            this._super(...arguments);
+            this.register(
+              'controller:application',
+              Controller.extend({
+                queryParams: ['lazyQueryParam'],
+              })
+            );
+
+            this.register(
+              'template:application',
+              compile('Engine<div class="lazy-query-param">{{this.lazyQueryParam}}</div>{{outlet}}')
+            );
+
+            this.register(
+              'route:application',
+              Route.extend({
+                queryParams: {
+                  lazyQueryParam: {
+                    defaultValue: null,
+                  },
+                },
+                deserializeQueryParam() {
+                  hooks.push('engine - deserialize query param');
+                  return 'foo';
+                },
+                model() {
+                  hooks.push('engine - application');
+                },
+              })
+            );
+          },
+        })
+      );
+
+      return this.visit('/blog?lazyQueryParam=bar', { shouldRender: true }).then(() => {
+        assert.deepEqual(
+          hooks,
+          ['application - application', 'engine - deserialize query param', 'engine - application'],
+          'the expected hooks were fired'
+        );
+        assert.strictEqual(this.element.querySelector('.lazy-query-param').innerHTML, 'foo');
+      });
+    }
   }
 );

packages/@ember/-internals/routing/lib/system/route.ts

@@ -2082,11 +2082,21 @@ export function getFullQueryParams(router: EmberRouter, state: TransitionState<R
     return state['fullQueryParams'];
   }
 
-  state['fullQueryParams'] = {};
-  Object.assign(state['fullQueryParams'], state.queryParams);
+  let fullQueryParamsState = {};
+  let haveAllRouteInfosResolved = state.routeInfos.every((routeInfo) => routeInfo.route);
 
-  router._deserializeQueryParams(state.routeInfos, state['fullQueryParams'] as QueryParam);
-  return state['fullQueryParams'];
+  Object.assign(fullQueryParamsState, state.queryParams);
+
+  router._deserializeQueryParams(state.routeInfos, fullQueryParamsState as QueryParam);
+
+  // only cache query params state if all routeinfos have resolved; it's possible
+  // for lazy routes to not have resolved when `getFullQueryParams` is called, so
+  // we wait until all routes have resolved prior to caching query params state
+  if (haveAllRouteInfosResolved) {
+    state['fullQueryParams'] = fullQueryParamsState;
+  }
+
+  return fullQueryParamsState;
 }
 
 function getQueryParamsFor(route: Route, state: TransitionState<Route>) {