Re-add "Skip merge commits""

README.md

@@ -140,6 +140,16 @@ The action will backport the pull request to each matched target branch.
 Note that the pull request's headref is excluded automatically.
 See [How it works](#how-it-works).
 
+### `merge_commits`
+
+Default: `fail`
+
+Specifies how the action should deal with merge commits on the merged pull request.
+
+- When set to `fail` the backport fails when the action detects one or more merge commits.
+- When set to `skip` the action only cherry-picks non-merge commits, i.e. it ignores merge commits.
+ This can be useful when you [keep your pull requests in sync with the base branch using merge commits](https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/proposing-changes-to-your-work-with-pull-requests/keeping-your-pull-request-in-sync-with-the-base-branch).
+
 ### `pull_description`
 
 Default:

action.yml

@@ -24,6 +24,12 @@ inputs:
  The action will backport the pull request to each matched target branch.
  Note that the pull request's headref is excluded automatically.
  default: ^backport ([^ ]+)$
+ merge_commits:
+ description: >
+ Specifies how the action should deal with merge commits on the merged pull request.
+ When set to `fail` the backport fails when the action detects one or more merge commits.
+ When set to `skip` the action only cherry-picks non-merge commits, i.e. it ignores merge commits.
+ default: fail
  pull_description:
  description: >
  Template used as description (i.e. body) in the pull requests created by this action.

src/backport.ts

@@ -11,7 +11,7 @@ type PRContent = {
  body: string;
 };
 
-type Config = {
+export type Config = {
  pwd: string;
  labels: {
  pattern?: RegExp;
@@ -22,6 +22,9 @@ type Config = {
  };
  copy_labels_pattern?: RegExp;
  target_branches?: string;
+ commits: {
+ merge_commits: "fail" | "skip";
+ };
 };
 
 enum Output {
@@ -78,12 +81,47 @@ export class Backport {
  mainpr.commits + 1, // +1 in case this concerns a shallowly cloned repo
  );
 
+ const commitShas = await this.github.getCommits(mainpr);
+ console.log(`Found commits: ${commitShas}`);
+
+ console.log("Checking the merged pull request for merge commits");
+ const mergeCommitShas = await this.git.findMergeCommits(
+ commitShas,
+ this.config.pwd,
+ );
  console.log(
- "Determining first and last commit shas, so we can cherry-pick the commit range",
+ `Encountered ${mergeCommitShas.length ?? "no"} merge commits`,
  );
+ if (
+ mergeCommitShas.length > 0 &&
+ this.config.commits.merge_commits == "fail"
+ ) {
+ const message = dedent`Backport failed because this pull request contains merge commits. \
+ You can either backport this pull request manually, or configure the action to skip merge commits.`;
+ console.error(message);
+ this.github.createComment({
+ owner,
+ repo,
+ issue_number: pull_number,
+ body: message,
+ });
+ return;
+ }
 
- const commitShas = await this.github.getCommits(mainpr);
- console.log(`Found commits: ${commitShas}`);
+ let commitShasToCherryPick = commitShas;
+ if (
+ mergeCommitShas.length > 0 &&
+ this.config.commits.merge_commits == "skip"
+ ) {
+ console.log("Skipping merge commits: " + mergeCommitShas);
+ const nonMergeCommitShas = commitShas.filter(
+ (sha) => !mergeCommitShas.includes(sha),
+ );
+ commitShasToCherryPick = nonMergeCommitShas;
+ }
+ console.log(
+ "Will cherry-pick the following commits: " + commitShasToCherryPick,
+ );
 
  let labelsToCopy: string[] = [];
  if (typeof this.config.copy_labels_pattern !== "undefined") {
@@ -154,7 +192,7 @@ export class Backport {
  }
 
  try {
- await this.git.cherryPick(commitShas, this.config.pwd);
+ await this.git.cherryPick(commitShasToCherryPick, this.config.pwd);
  } catch (error) {
  const message = this.composeMessageForBackportScriptFailure(
  target,

src/git.ts

@@ -52,6 +52,27 @@ export class Git {
  }
  }
 
+ public async findMergeCommits(
+ commitShas: string[],
+ pwd: string,
+ ): Promise<string[]> {
+ const range = `${commitShas[0]}^..${commitShas[commitShas.length - 1]}`;
+ const { exitCode, stdout } = await this.git(
+ "rev-list",
+ ["--merges", range],
+ pwd,
+ );
+ if (exitCode !== 0) {
+ throw new Error(
+ `'git rev-list --merges ${range}' failed with exit code ${exitCode}`,
+ );
+ }
+ const mergeCommitShas = stdout
+ .split("\n")
+ .filter((sha) => sha.trim() !== "");
+ return mergeCommitShas;
+ }
+
  public async push(branchname: string, pwd: string) {
  const { exitCode } = await this.git(
  "push",

src/main.ts

@@ -1,5 +1,5 @@
 import * as core from "@actions/core";
-import { Backport } from "./backport";
+import { Backport, Config } from "./backport";
 import { Github } from "./github";
 import { Git } from "./git";
 import { execa } from "execa";
@@ -17,17 +17,25 @@ async function run(): Promise<void> {
  const title = core.getInput("pull_title");
  const copy_labels_pattern = core.getInput("copy_labels_pattern");
  const target_branches = core.getInput("target_branches");
+ const merge_commits = core.getInput("merge_commits");
+
+ if (merge_commits != "fail" && merge_commits != "skip") {
+ const message = `Expected input 'merge_commits' to be either 'fail' or 'skip', but was '${merge_commits}'`;
+ console.error(message);
+ core.setFailed(message);
+ return;
+ }
 
  const github = new Github(token);
  const git = new Git(execa);
- const config = {
+ const config: Config = {
  pwd,
  labels: { pattern: pattern === "" ? undefined : new RegExp(pattern) },
  pull: { description, title },
  copy_labels_pattern:
  copy_labels_pattern === "" ? undefined : new RegExp(copy_labels_pattern),
- target_branches:
-  target_branches === "" ? undefined : (target_branches as string),
+ target_branches: target_branches === "" ? undefined : target_branches,
+ commits: { merge_commits },
  };
  const backport = new Backport(github, config, git);
 

src/test/git.test.ts

@@ -44,3 +44,24 @@ describe("git.cherryPick", () => {
  });
  });
 });
+
+describe("git.findMergeCommits", () => {
+ describe("throws Error", () => {
+ it("when failing with an unpexected non-zero exit code", async () => {
+ response.exitCode = 1;
+ await expect(git.findMergeCommits(["unknown"], "")).rejects.toThrowError(
+ `'git rev-list --merges unknown^..unknown' failed with exit code 1`,
+ );
+ });
+ });
+
+ describe("returns all merge commits", () => {
+ it("when git rev-list outputs them", async () => {
+ response.exitCode = 0;
+ response.stdout = "two\nfour";
+ expect(
+ await git.findMergeCommits(["one", "two", "three", "four"], ""),
+ ).toEqual(["two", "four"]);
+ });
+ });
+});