Short-circuited resource URL regeneration when it's not necessary

refs https://github.com/TryGhost/Toolbox/issues/503

- Full URL regeneration process was happening even when only unrelated to URL generation fields were updated (e.g. 'plaintext' change in post does not affect the URL of the post). Stopping the  "resource updated" event processing early circumvents full url regeneration inside of DynamicRouting, which can be quite heavy depending on routing configuration
- The URLResourceUpdatedEvent is supposed to be emmited whenever there's an update to the resource already associated with the URL and no url-affecting fields were touched.

ghost/core/core/server/services/url/Resources.js

@@ -1,5 +1,7 @@
 const _ = require('lodash');
 const debug = require('@tryghost/debug')('services:url:resources');
+const DomainEvents = require('@tryghost/domain-events');
+const {URLResourceUpdatedEvent} = require('@tryghost/dynamic-routing-events');
 const Resource = require('./Resource');
 const config = require('../../../shared/config');
 const models = require('../../models');
@@ -297,6 +299,25 @@ class Resources {
 
         const resourceConfig = _.find(this.resourcesConfig, {type: type});
 
+        if (resourceConfig && Object.keys(model._changed).length) {
+            const ignoredProperties = [...resourceConfig.modelOptions.exclude, 'updated_at'];
+            const containsRouteAffectingChanges = _.difference(Object.keys(model._changed), ignoredProperties).length !== 0;
+
+            if (!containsRouteAffectingChanges) {
+                const cachedResource = this.getByIdAndType(type, model.id);
+
+                if (cachedResource && Object.keys(model._changed).includes('updated_at')) {
+                    DomainEvents.dispatch(URLResourceUpdatedEvent.create(Object.assign(cachedResource.data, {
+                        resourceType: cachedResource.config.type,
+                        updated_at: model._changed.updated_at
+                    })));
+                }
+
+                debug('skipping _onResourceUpdated because only non-route-related properties changed');
+                return false;
+            }
+        }
+
         // NOTE: synchronous handling for post and pages so that their URL is available without a delay
         //       for more context and future improvements check https://github.com/TryGhost/Ghost/issues/10360
         if (['posts', 'pages'].includes(type)) {

ghost/core/test/unit/server/services/url/Resources.test.js

@@ -0,0 +1,36 @@
+const assert = require('assert');
+
+const Resources = require('../../../../../core/server/services/url/Resources');
+
+describe('Unit: services/url/Resources', function () {
+    describe('_onResourceUpdated', function () {
+        it('does not start the queue when non-routing properties were changed', async function () {
+            const resources = new Resources({
+                resourcesConfig: [{
+                    type: 'post',
+                    modelOptions: {
+                        modelName: 'Post',
+                        exclude: [
+                            'title',
+                            'mobiledoc',
+                            'lexical',
+                            'html',
+                            'plaintext'
+                        ]
+                    }
+                }]
+            });
+
+            const postModelMock = {
+                _changed: {
+                    title: 'New Title',
+                    plaintext: 'New plaintext'
+                }
+            };
+
+            const updated = await resources._onResourceUpdated('post', postModelMock);
+
+            assert.equal(updated, false);
+        });
+    });
+});