Fetch necessary git refs

.github/workflows/backport.yml

@@ -21,9 +21,6 @@ jobs:
       )
     steps:
       - uses: actions/checkout@v2
-        with:
-          # Required to find all branches
-          fetch-depth: 0
       - name: Create backport PRs
         uses: zeebe-io/backport-action@master
         with:

README.md

@@ -46,9 +46,6 @@ jobs:
     if: github.event.pull_request.merged
     steps:
       - uses: actions/checkout@v2
-        with:
-          # Required to find all branches
-          fetch-depth: 0
       - name: Create backport PRs
         uses: zeebe-io/backport-action@master
         with:
@@ -107,9 +104,6 @@ jobs:
       )
     steps:
       - uses: actions/checkout@v2
-        with:
-          # Required to find all branches
-          fetch-depth: 0
       - name: Create backport PRs
         uses: zeebe-io/backport-action@master
         with:

src/backport.ts

@@ -62,6 +62,15 @@ export class Backport {
         `Detected labels on PR: ${labels.map((label) => label.name)}`
       );
 
+      if (!someLabelIn(labels).matches(this.config.labels.pattern)) {
+        console.log(
+          `Nothing to backport: none of the labels match the backport pattern '${this.config.labels.pattern.source}'`
+        );
+        return; // nothing left to do here
+      }
+
+      await git.fetch(`refs/pull/${pull_number}/head`, this.config.pwd);
+
       for (const label of labels) {
         console.log(`Working on label ${label.name}`);
 
@@ -86,6 +95,8 @@ export class Backport {
         const target = match[1];
         console.log(`Found target in label: ${target}`);
 
+        await git.fetch(target, this.config.pwd);
+
         try {
           const branchname = `backport-${pull_number}-to-${target}`;
 
@@ -289,3 +300,17 @@ export class Backport {
     return dedent`Successfully created backport PR #${pr_number} for \`${target}\`.`;
   }
 }
+
+/**
+ * Helper method for label arrays to check that it matches a particular pattern
+ *
+ * @param labels an array of labels
+ * @returns a 'curried' function to easily test for a matching a label
+ */
+function someLabelIn(labels: { name: string }[]): {
+  matches: (pattern: RegExp) => boolean;
+} {
+  return {
+    matches: (pattern) => labels.some((l) => pattern.test(l.name)),
+  };
+}

src/git.ts

@@ -1,5 +1,20 @@
 import execa from "execa";
 
+/**
+ * Fetches a ref from origin
+ *
+ * @param ref the sha, branchname, etc to fetch
+ * @param pwd the root of the git repository
+ */
+export async function fetch(ref: string, pwd: string) {
+  const { exitCode } = await git("fetch", ["origin", ref], pwd);
+  if (exitCode !== 0) {
+    throw new Error(
+      `'git fetch origin ${ref}' failed with exit code ${exitCode}`
+    );
+  }
+}
+
 /**
  * Performs the backport
  *

src/test/backport.test.ts

@@ -30,6 +30,11 @@ describe("the backport action", () => {
       await backport.run();
       expect(mockedDefaultGithub.createComment).toHaveBeenCalledTimes(0);
     });
+
+    it("does not fetch the pull request's head", async () => {
+      await backport.run();
+      expect(mockedGit.fetch).toHaveBeenCalledTimes(0);
+    });
   });
 
   describe("given a payload for a PR with backport label", () => {
@@ -89,6 +94,14 @@ describe("the backport action", () => {
       beforeEach(() => {
         mockedGit.performBackport.mockResolvedValue(0);
       });
+      it("fetches the pull request's head", async () => {
+        await backport.run();
+        expect(mockedGit.fetch).toHaveBeenCalledWith(
+          "refs/pull/1347/head",
+          config.pwd
+        );
+        expect(mockedGit.fetch).toHaveBeenCalledWith("stable/0.25", config.pwd);
+      });
       it("pushes the commits to origin", async () => {
         mockedGit.push.mockResolvedValue(0);
         await backport.run();