🐛 Fixed meta attributes calculation on post preview

closes https://github.com/TryGhost/Ghost/issues/12247

- Internal preview controller was lacking "mapping" call to post object which handled not only missing meta attribute information but lots of other mappings (e.g. users, tags, etc.)
- Have added a regression test to catch issues like this in the future

core/server/api/canary/utils/serializers/output/preview.js

@@ -1,7 +1,9 @@
+const mapper = require('./utils/mapper');
+
 module.exports = {
     all(model, apiConfig, frame) {
         frame.response = {
-            preview: [model.toJSON(frame.options)]
+            preview: [mapper.mapPost(model, frame)]
         };
     }
 };

core/server/api/v2/utils/serializers/output/preview.js

@@ -1,7 +1,9 @@
+const mapper = require('./utils/mapper');
+
 module.exports = {
     all(model, apiConfig, frame) {
         frame.response = {
-            preview: [model.toJSON(frame.options)]
+            preview: [mapper.mapPost(model, frame)]
         };
     }
 };

test/regression/site/frontend_spec.js

@@ -253,6 +253,8 @@ describe('Frontend Routing', function () {
                         should.exist(res.headers.date);
 
                         $('title').text().should.equal('Not finished yet');
+                        $('meta[name="description"]').attr('content').should.equal('meta description for draft post');
+
                         // @TODO: use theme from fixtures and don't rely on content/themes/casper
                         // $('.content .post').length.should.equal(1);
                         // $('.poweredby').text().should.equal('Proudly published with Ghost');

test/utils/fixtures/data-generator.js

@@ -809,6 +809,11 @@ DataGenerator.forKnex = (function () {
             id: ObjectId.generate(),
             post_id: DataGenerator.Content.posts[2].id,
             meta_description: 'test stuff'
+        },
+        {
+            id: ObjectId.generate(),
+            post_id: DataGenerator.Content.posts[3].id,
+            meta_description: 'meta description for draft post'
         }
     ];