Change query to get the latest SHA in the pipeline editor

This fixes the editor not working with branches as the
previous query would return empty for merged results
among other scenarios

app/assets/javascripts/pipeline_editor/graphql/queries/latest_commit_sha.query.graphql

 query getLatestCommitSha($projectPath: ID!, $ref: String) {
   project(fullPath: $projectPath) {
-    pipelines(ref: $ref) {
-      nodes {
-        id
-        sha
-        path
-        commitPath
+    repository {
+      tree(ref: $ref) {
+        lastCommit {
+          sha
+        }
       }
     }
   }

app/assets/javascripts/pipeline_editor/pipeline_editor_app.vue

@@ -164,22 +164,8 @@ export default {
         };
       },
       update(data) {
-        const pipelineNodes = data.project?.pipelines?.nodes ?? [];
+        const latestCommitSha = data.project?.repository?.tree?.lastCommit?.sha;
 
-        // it's possible to query for the commit sha too early after an update
-        // (e.g. after committing a new branch, we might query for the commit sha
-        // but the pipeline nodes are still empty).
-        // in this case, we start polling until we get a commit sha.
-        if (pipelineNodes.length === 0) {
-          if (![EDITOR_APP_STATUS_LOADING, EDITOR_APP_STATUS_EMPTY].includes(this.appStatus)) {
-            this.$apollo.queries.commitSha.startPolling(COMMIT_SHA_POLL_INTERVAL);
-            return this.commitSha;
-          }
-
-          return '';
-        }
-
-        const latestCommitSha = pipelineNodes[0].sha;
         if (this.isFetchingCommitSha && latestCommitSha === this.commitSha) {
           this.$apollo.queries.commitSha.startPolling(COMMIT_SHA_POLL_INTERVAL);
           return this.commitSha;

spec/frontend/pipeline_editor/mock_data.js

@@ -159,15 +159,12 @@ export const mergeUnwrappedCiConfig = (mergedConfig) => {
 export const mockCommitShaResults = {
   data: {
     project: {
-      pipelines: {
-        nodes: [
-          {
-            id: 'gid://gitlab/Ci::Pipeline/1',
+      repository: {
+        tree: {
+          lastCommit: {
             sha: mockCommitSha,
-            path: `/${mockProjectFullPath}/-/pipelines/488`,
-            commitPath: `/${mockProjectFullPath}/-/commit/d0d56d363d8a3f67a8ab9fc00207d468f30032ca`,
           },
-        ],
+        },
       },
     },
   },
@@ -176,21 +173,12 @@ export const mockCommitShaResults = {
 export const mockNewCommitShaResults = {
   data: {
     project: {
-      pipelines: {
-        nodes: [
-          {
-            id: 'gid://gitlab/Ci::Pipeline/2',
+      repository: {
+        tree: {
+          lastCommit: {
             sha: 'eeff1122',
-            path: `/${mockProjectFullPath}/-/pipelines/489`,
-            commitPath: `/${mockProjectFullPath}/-/commit/bb1abcfe3d8a3f67a8ab9fc00207d468f3022bee`,
           },
-          {
-            id: 'gid://gitlab/Ci::Pipeline/1',
-            sha: mockCommitSha,
-            path: `/${mockProjectFullPath}/-/pipelines/488`,
-            commitPath: `/${mockProjectFullPath}/-/commit/d0d56d363d8a3f67a8ab9fc00207d468f30032ca`,
-          },
-        ],
+        },
       },
     },
   },
@@ -199,8 +187,12 @@ export const mockNewCommitShaResults = {
 export const mockEmptyCommitShaResults = {
   data: {
     project: {
-      pipelines: {
-        nodes: [],
+      repository: {
+        tree: {
+          lastCommit: {
+            sha: '',
+          },
+        },
       },
     },
   },

spec/frontend/pipeline_editor/pipeline_editor_app_spec.js

@@ -283,19 +283,6 @@ describe('Pipeline editor app component', () => {
           expect(window.scrollTo).toHaveBeenCalledWith({ top: 0, behavior: 'smooth' });
         });
 
-        it('polls for commit sha while pipeline data is not yet available for newly committed branch', async () => {
-          jest
-            .spyOn(wrapper.vm.$apollo.queries.commitSha, 'startPolling')
-            .mockImplementation(jest.fn());
-
-          // simulate updating current branch (which triggers commitSha refetch)
-          // while pipeline data is not yet available
-          mockLatestCommitShaQuery.mockResolvedValue(mockEmptyCommitShaResults);
-          await wrapper.vm.$apollo.queries.commitSha.refetch();
-
-          expect(wrapper.vm.$apollo.queries.commitSha.startPolling).toHaveBeenCalledTimes(1);
-        });
-
         it('polls for commit sha while pipeline data is not yet available for current branch', async () => {
           jest
             .spyOn(wrapper.vm.$apollo.queries.commitSha, 'startPolling')