feat(create-pr): update pr with base branch first (#211)

src/helpers/create-pr.ts

@@ -24,21 +24,30 @@ export class CreatePR extends HelperInputs {
 
 export const createPr = async ({ title, body, head = context.ref.replace('refs/heads/', ''), base }: CreatePR) => {
   const pr_base = base || (await getDefaultBranch());
-  const result = await octokit.pulls.create({
+  await updateHeadWithBaseBranch(pr_base, head);
+  const {
+    data: { number }
+  } = await octokit.pulls.create({
     title,
     head,
     base: pr_base,
     body,
     maintainer_can_modify: true,
     ...context.repo
   });
-  const pullNumber = result?.data?.number;
-  return pullNumber;
+  return number;
 };
 
-async function getDefaultBranch() {
+const updateHeadWithBaseBranch = (base: string, head: string) =>
+  octokit.repos.merge({
+    base: head,
+    head: base,
+    ...context.repo
+  });
+
+const getDefaultBranch = async () => {
   const {
     data: { default_branch }
   } = await octokit.repos.get({ ...context.repo });
   return default_branch;
-}
+};

test/helpers/create-pr.test.ts

@@ -21,7 +21,7 @@ jest.mock('@actions/github', () => ({
   context: { repo: { repo: 'repo', owner: 'owner' }, ref: 'refs/heads/source' },
   getOctokit: jest.fn(() => ({
     rest: {
-      repos: { get: jest.fn() },
+      repos: { get: jest.fn(), merge: jest.fn() },
       pulls: { create: jest.fn() }
     }
   }))
@@ -50,6 +50,18 @@ describe('createPr', () => {
     expect(octokit.repos.get).toHaveBeenCalledWith({ ...context.repo });
   });
 
+  it('should call repos merge with correct params', async () => {
+    await createPr({
+      title,
+      body
+    });
+    expect(octokit.repos.merge).toHaveBeenCalledWith({
+      base: 'source',
+      head: 'default branch',
+      ...context.repo
+    });
+  });
+
   it('should call create with correct params', async () => {
     await createPr({
       title,