Improve files_decorator performance

**How?**
Previously the files_decorator inserted parent folders inefficiently.
It started at the first part and ensured each was inserted.

Since the file entries are given to use in alphabetical order, we can
start at the last part of the blob's parents. If this exists, we can
short circuit and be done inserting parents.

**What else?**
- Improve performance of decorateData. The object spread operator is
not needed because the object is brand new.

2 files changed, 84 insertions, 0 deletions

diff --git a/spec/javascripts/ide/lib/files_spec.js b/spec/javascripts/ide/lib/files_spec.js
new file mode 100644
index 00000000000..fe791aa2b74
--- /dev/null
+++ b/spec/javascripts/ide/lib/files_spec.js
@@ -0,0 +1,77 @@
+import { viewerInformationForPath } from '~/vue_shared/components/content_viewer/lib/viewer_utils';
+import { decorateFiles, splitParent } from '~/ide/lib/files';
+import { decorateData } from '~/ide/stores/utils';
+
+const TEST_BRANCH_ID = 'lorem-ipsum';
+const TEST_PROJECT_ID = 10;
+
+const createEntries = paths => {
+  const createEntry = (acc, { path, type, children }) => {
+    // Sometimes we need to end the url with a '/'
+    const createUrl = base => (type === 'tree' ? `${base}/` : base);
+
+    const { name, parent } = splitParent(path);
+    const parentEntry = acc[parent];
+
+    acc[path] = {
+      ...decorateData({
+        projectId: TEST_PROJECT_ID,
+        branchId: TEST_BRANCH_ID,
+        id: path,
+        name,
+        path,
+        url: createUrl(`/${TEST_PROJECT_ID}/${type}/${TEST_BRANCH_ID}/-/${path}`),
+        type,
+        previewMode: viewerInformationForPath(path),
+        parentPath: parent,
+        parentTreeUrl: parentEntry
+          ? parentEntry.url
+          : createUrl(`/${TEST_PROJECT_ID}/${type}/${TEST_BRANCH_ID}`),
+      }),
+      tree: children.map(childName => jasmine.objectContaining({ name: childName })),
+    };
+
+    return acc;
+  };
+
+  const entries = paths.reduce(createEntry, {});
+
+  // Wrap entries in jasmine.objectContaining.
+  // We couldn't do this earlier because we still need to select properties from parent entries.
+  return Object.keys(entries).reduce((acc, key) => {
+    acc[key] = jasmine.objectContaining(entries[key]);
+
+    return acc;
+  }, {});
+};
+
+describe('IDE lib decorate files', () => {
+  it('creates entries and treeList', () => {
+    const data = ['app/assets/apples/foo.js', 'app/bugs.js', 'README.md'];
+    const expectedEntries = createEntries([
+      { path: 'app', type: 'tree', children: ['assets', 'bugs.js'] },
+      { path: 'app/assets', type: 'tree', children: ['apples'] },
+      { path: 'app/assets/apples', type: 'tree', children: ['foo.js'] },
+      { path: 'app/assets/apples/foo.js', type: 'blob', children: [] },
+      { path: 'app/bugs.js', type: 'blob', children: [] },
+      { path: 'README.md', type: 'blob', children: [] },
+    ]);
+
+    const { entries, treeList } = decorateFiles({
+      data,
+      branchId: TEST_BRANCH_ID,
+      projectId: TEST_PROJECT_ID,
+    });
+
+    // Here we test the keys and then each key/value individually because `expect(entries).toEqual(expectedEntries)`
+    // was taking a very long time for some reason. Probably due to large objects and nested `jasmine.objectContaining`.
+    const entryKeys = Object.keys(entries);
+
+    expect(entryKeys).toEqual(Object.keys(expectedEntries));
+    entryKeys.forEach(key => {
+      expect(entries[key]).toEqual(expectedEntries[key]);
+    });
+
+    expect(treeList).toEqual([expectedEntries.app, expectedEntries['README.md']]);
+  });
+});
diff --git a/spec/javascripts/ide/stores/actions/tree_spec.js b/spec/javascripts/ide/stores/actions/tree_spec.js
index bd41e87bf0e..fbb676aab33 100644
--- a/spec/javascripts/ide/stores/actions/tree_spec.js
+++ b/spec/javascripts/ide/stores/actions/tree_spec.js
@@ -20,6 +20,7 @@ describe('Multi-file store tree actions', () => {
   };
 
   beforeEach(() => {
+    jasmine.clock().install();
     spyOn(router, 'push');
 
     mock = new MockAdapter(axios);
@@ -37,6 +38,7 @@ describe('Multi-file store tree actions', () => {
   });
 
   afterEach(() => {
+    jasmine.clock().uninstall();
     mock.restore();
     resetStore(store);
   });
@@ -70,6 +72,11 @@ describe('Multi-file store tree actions', () => {
         store
           .dispatch('getFiles', basicCallParameters)
           .then(() => {
+            // The populating of the tree is deferred for performance reasons.
+            // See this merge request for details: https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/25700
+            jasmine.clock().tick(1);
+          })
+          .then(() => {
             projectTree = store.state.trees['abcproject/master'];
 
             expect(projectTree.tree.length).toBe(2);