feat: allow backporting to remote repository

README.md

@@ -169,6 +169,19 @@ When enabled, the action detects the method used to merge the pull request.
 
 By default, the action always cherry-picks the commits from the pull request.
 
+##### `downstream_repo`
+
+Define if you want to backport to a repository other than where the workflow runs.
+
+By default, the action always backports to the repository in which the workflow runs.
+
+##### `downstream_owner`
+
+Define if you want to backport to another owner than the owner of the repository the workflow runs on.
+Only takes effect if the `downstream_repo` property is also defined.
+
+By default, uses the owner of the repository in which the workflow runs.
+
 ### `github_token`
 
 Default: `${{ github.token }}`

action.yml

@@ -44,6 +44,19 @@ inputs:
       - For "Merged as a merge commit", the action cherry-picks the commits from the pull request.
 
       By default, the action always cherry-picks the commits from the pull request.
+
+      #### `downstream_repo`
+
+      Define if you want to backport to a repository other than where the workflow runs.
+
+      By default, the action always backports to the repository in which the workflow runs.
+
+      #### `downstream_owner`
+
+      Define if you want to backport to another owner than the owner of the repository the workflow runs on.
+      Only takes effect if the `downstream_repo` property is also defined.
+
+      By default, uses the owner of the repository in which the workflow runs.
     default: >
       {
         "detect_merge_method": false

src/backport.ts

@@ -38,9 +38,13 @@ export type Config = {
 
 type Experimental = {
   detect_merge_method: boolean;
+  downstream_repo?: string;
+  downstream_owner?: string;
 };
 const experimentalDefaults: Experimental = {
   detect_merge_method: false,
+  downstream_repo: undefined,
+  downstream_owner: undefined,
 };
 export { experimentalDefaults };
 
@@ -55,25 +59,53 @@ export class Backport {
   private config;
   private git;
 
+  private downstreamRepo;
+  private downstreamOwner;
+
   constructor(github: GithubApi, config: Config, git: Git) {
     this.github = github;
     this.config = config;
     this.git = git;
+
+    this.downstreamRepo = this.config.experimental.downstream_repo ?? undefined;
+    this.downstreamOwner =
+      this.config.experimental.downstream_owner ?? undefined;
+  }
+
+  shouldUseDownstreamRepo(): boolean {
+    return !!this.downstreamRepo;
+  }
+
+  getRemote(): "downstream" | "origin" {
+    return this.shouldUseDownstreamRepo() ? "downstream" : "origin";
   }
 
   async run(): Promise<void> {
     try {
       const payload = this.github.getPayload();
-      const owner = this.github.getRepo().owner;
-      const repo = payload.repository?.name ?? this.github.getRepo().repo;
+
+      const workflowOwner = this.github.getRepo().owner;
+      const owner =
+        this.shouldUseDownstreamRepo() && this.downstreamOwner // if undefined, use owner of workflow
+          ? this.downstreamOwner
+          : workflowOwner;
+
+      const workflowRepo =
+        payload.repository?.name ?? this.github.getRepo().repo;
+      const repo = this.shouldUseDownstreamRepo()
+        ? this.downstreamRepo
+        : workflowRepo;
+
+      if (repo === undefined) throw new Error("No repository defined!");
+
       const pull_number = this.github.getPullNumber();
       const mainpr = await this.github.getPullRequest(pull_number);
 
       if (!(await this.github.isMerged(mainpr))) {
         const message = "Only merged pull requests can be backported.";
         this.github.createComment({
-          owner,
-          repo,
+          owner: workflowOwner,
+          repo: workflowRepo,
           issue_number: pull_number,
           body: message,
         });
@@ -172,8 +204,8 @@ export class Backport {
           You can either backport this pull request manually, or configure the action to skip merge commits.`;
         console.error(message);
         this.github.createComment({
-          owner,
-          repo,
+          owner: workflowOwner,
+          repo: workflowRepo,
           issue_number: pull_number,
           body: message,
         });
@@ -210,21 +242,25 @@ export class Backport {
         `Will copy labels matching ${this.config.copy_labels_pattern}. Found matching labels: ${labelsToCopy}`,
       );
 
+      if (this.shouldUseDownstreamRepo()) {
+        await this.git.remoteAdd(this.config.pwd, "downstream", owner, repo);
+      }
+
       const successByTarget = new Map<string, boolean>();
       const createdPullRequestNumbers = new Array<number>();
       for (const target of target_branches) {
         console.log(`Backporting to target branch '${target}...'`);
 
         try {
-          await this.git.fetch(target, this.config.pwd, 1);
+          await this.git.fetch(target, this.config.pwd, 1, this.getRemote());
         } catch (error) {
           if (error instanceof GitRefNotFoundError) {
             const message = this.composeMessageForFetchTargetFailure(error.ref);
             console.error(message);
             successByTarget.set(target, false);
             await this.github.createComment({
-              owner,
-              repo,
+              owner: workflowOwner,
+              repo: workflowRepo,
               issue_number: pull_number,
               body: message,
             });
@@ -245,7 +281,7 @@ export class Backport {
           try {
             await this.git.checkout(
               branchname,
-              `origin/${target}`,
+              `${this.getRemote()}/${target}`,
               this.config.pwd,
             );
           } catch (error) {
@@ -257,8 +293,8 @@ export class Backport {
             console.error(message);
             successByTarget.set(target, false);
             await this.github.createComment({
-              owner,
-              repo,
+              owner: workflowOwner,
+              repo: workflowRepo,
               issue_number: pull_number,
               body: message,
             });
@@ -276,16 +312,20 @@ export class Backport {
             console.error(message);
             successByTarget.set(target, false);
             await this.github.createComment({
-              owner,
-              repo,
+              owner: workflowOwner,
+              repo: workflowRepo,
               issue_number: pull_number,
               body: message,
             });
             continue;
           }
 
-          console.info(`Push branch to origin`);
-          const pushExitCode = await this.git.push(branchname, this.config.pwd);
+          console.info(`Push branch to ${this.getRemote()}`);
+          const pushExitCode = await this.git.push(
+            branchname,
+            this.getRemote(),
+            this.config.pwd,
+          );
           if (pushExitCode != 0) {
             const message = this.composeMessageForGitPushFailure(
               target,
@@ -294,8 +334,8 @@ export class Backport {
             console.error(message);
             successByTarget.set(target, false);
             await this.github.createComment({
-              owner,
-              repo,
+              owner: workflowOwner,
+              repo: workflowRepo,
               issue_number: pull_number,
               body: message,
             });
@@ -320,8 +360,8 @@ export class Backport {
             const message =
               this.composeMessageForCreatePRFailed(new_pr_response);
             await this.github.createComment({
-              owner,
-              repo,
+              owner: workflowOwner,
+              repo: workflowRepo,
               issue_number: pull_number,
               body: message,
             });
@@ -350,6 +390,10 @@ export class Backport {
               const set_assignee_response = await this.github.setAssignees(
                 new_pr.number,
                 assignees,
+                {
+                  owner,
+                  repo,
+                },
               );
               if (set_assignee_response.status != 201) {
                 console.error(JSON.stringify(set_assignee_response));
@@ -364,7 +408,8 @@ export class Backport {
             if (reviewers?.length > 0) {
               console.info("Setting reviewers " + reviewers);
               const reviewRequest = {
-                ...this.github.getRepo(),
+                owner,
+                repo,
                 pull_number: new_pr.number,
                 reviewers: reviewers,
               };
@@ -380,19 +425,27 @@ export class Backport {
             const label_response = await this.github.labelPR(
               new_pr.number,
               labelsToCopy,
+              {
+                owner,
+                repo,
+              },
             );
             if (label_response.status != 200) {
               console.error(JSON.stringify(label_response));
               // The PR was still created so let's still comment on the original.
             }
           }
 
-          const message = this.composeMessageForSuccess(new_pr.number, target);
+          const message = this.composeMessageForSuccess(
+            new_pr.number,
+            target,
+            this.shouldUseDownstreamRepo() ? `${owner}/${repo}` : "",
+          );
           successByTarget.set(target, true);
           createdPullRequestNumbers.push(new_pr.number);
           await this.github.createComment({
-            owner,
-            repo,
+            owner: workflowOwner,
+            repo: workflowRepo,
             issue_number: pull_number,
             body: message,
           });
@@ -401,8 +454,8 @@ export class Backport {
             console.error(error.message);
             successByTarget.set(target, false);
             await this.github.createComment({
-              owner,
-              repo,
+              owner: workflowOwner,
+              repo: workflowRepo,
               issue_number: pull_number,
               body: error.message,
             });
@@ -515,9 +568,13 @@ export class Backport {
                 (see action log for full response)`;
   }
 
-  private composeMessageForSuccess(pr_number: number, target: string) {
+  private composeMessageForSuccess(
+    pr_number: number,
+    target: string,
+    downstream: string,
+  ) {
     return dedent`Successfully created backport PR for \`${target}\`:
-                  - #${pr_number}`;
+                  - ${downstream}#${pr_number}`;
   }
 
   private createOutput(

src/git.ts

@@ -31,23 +31,55 @@ export class Git {
    * @param ref the sha, branchname, etc to fetch
    * @param pwd the root of the git repository
    * @param depth the number of commits to fetch
+   * @param remote the shortname of the repository from where to fetch commits
    * @throws GitRefNotFoundError when ref not found
    * @throws Error for any other non-zero exit code
    */
-  public async fetch(ref: string, pwd: string, depth: number) {
+  public async fetch(
+    ref: string,
+    pwd: string,
+    depth: number,
+    remote: string = "origin",
+  ) {
     const { exitCode } = await this.git(
       "fetch",
-      [`--depth=${depth}`, "origin", ref],
+      [`--depth=${depth}`, remote, ref],
       pwd,
     );
     if (exitCode === 128) {
       throw new GitRefNotFoundError(
-        `Expected to fetch '${ref}', but couldn't find it`,
+        `Expected to fetch '${ref}' from '${remote}', but couldn't find it`,
         ref,
       );
     } else if (exitCode !== 0) {
       throw new Error(
-        `'git fetch origin ${ref}' failed with exit code ${exitCode}`,
+        `'git fetch ${remote} ${ref}' failed with exit code ${exitCode}`,
+      );
+    }
+  }
+
+  /**
+   * Adds a new remote Git repository as a shortname.
+   *
+   * @param pwd the root of the git repository
+   * @param shortname the shortname referencing the repository
+   * @param owner the owner of the GitHub repository
+   * @param repo the name of the repository
+   */
+  public async remoteAdd(
+    pwd: string,
+    shortname: string,
+    owner: string | undefined,
+    repo: string | undefined,
+  ) {
+    const { exitCode } = await this.git(
+      "remote",
+      ["add", shortname, `https://github.com/${owner}/${repo}.git`],
+      pwd,
+    );
+    if (exitCode !== 0) {
+      throw new Error(
+        `'git remote add ${owner}/${repo}' failed with exit code ${exitCode}`,
       );
     }
   }
@@ -94,10 +126,10 @@ export class Git {
     return mergeCommitShas;
   }
 
-  public async push(branchname: string, pwd: string) {
+  public async push(branchname: string, remote: string, pwd: string) {
     const { exitCode } = await this.git(
       "push",
-      ["--set-upstream", "origin", branchname],
+      ["--set-upstream", remote, branchname],
       pwd,
     );
     return exitCode;