🐛 only save imported post ids if amp field is empty

closes TryGhost#8963
- if an LTS export is imported into a 1.0 blog, then the 1.0 blog is
exported and re-imported into another 1.0 blog, any post ids from the
lts import were getting clobbered. This only saves the post id if the
amp field does not already exist
- add failing test that passes w/change

core/server/data/importer/importers/data/posts.js

@@ -139,7 +139,10 @@ class PostsImporter extends BaseImporter {
             }
 
             // NOTE: we remember the old post id for disqus
-            if (model.id) {
+            // We also check if amp already exists to prevent
+            // overwriting any comment ids from a 1.0 export
+            // (see https://github.com/TryGhost/Ghost/issues/8963)
+            if (model.id && !model.amp) {
                 model.amp = model.id.toString();
             }
         });

core/test/integration/data/importer/importers/data_spec.js

@@ -1450,6 +1450,8 @@ describe('Import (new test structure)', function () {
 
                     // Check post language is null
                     should(firstPost.locale).equal(null);
+                    // Check post id has been inserted into amp column
+                    should(firstPost.amp).equal(exportData.data.posts[0].id.toString());
                     // Check user language is null
                     should(users[1].locale).equal(null);
 
@@ -1658,4 +1660,30 @@ describe('Import (new test structure)', function () {
                 }).catch(done);
         });
     });
+
+    describe('1.0: basic import test', function () {
+        var exportData;
+
+        before(function doImport() {
+            // initialize the blog with some data
+            return testUtils.initFixtures('roles', 'owner', 'settings').then(function () {
+                return testUtils.fixtures.loadExportFixture('export-basic-test');
+            }).then(function (exported) {
+                exportData = exported.db[0];
+                return dataImporter.doImport(exportData);
+            });
+        });
+
+        after(testUtils.teardown);
+
+        it('keeps the value of the amp field', function () {
+            return knex('posts').select().then(function (posts) {
+                should.exist(posts);
+
+                posts.length.should.eql(exportData.data.posts.length);
+                posts[0].amp.should.eql(exportData.data.posts[0].amp);
+                posts[1].amp.should.eql(exportData.data.posts[1].id);
+            });
+        });
+    });
 });