Add default_mainline input

README.md

@@ -113,6 +113,15 @@ Regex pattern to match github labels which will be copied from the original pull
 Note that labels matching `label_pattern` are excluded.
 By default, no labels are copied.
 
+### `default_mainline`
+
+Default: `''` (disabled)
+
+The mainline (parent-number) to use when cherry-picking.
+This allows the action to cherry-pick merge commits.
+See https://git-scm.com/docs/git-cherry-pick for more information.
+By default, the action fails when it encounters a merge commit.
+
 ### `github_token`
 
 Default: `${{ github.token }}`

action.yml

@@ -8,6 +8,12 @@ inputs:
       Regex pattern to match github labels which will be copied from the original pull request to the backport pull request.
       Note that labels matching `label_pattern` are excluded.
       By default, no labels are copied.
+  default_mainline:
+    description: >
+      The mainline (parent-number) to use when cherry-picking.
+      This allows the action to cherry-pick merge commits.
+      See https://git-scm.com/docs/git-cherry-pick for more information.
+      By default, the action fails when it encounters a merge commit.
   github_token:
     description: >
       Token to authenticate requests to GitHub.

dist/index.js

@@ -140,7 +140,7 @@ class Backport {
                             continue;
                         }
                         try {
-                            yield git.cherryPick(commitShas, this.config.pwd);
+                            yield git.cherryPick(commitShas, this.config.pwd, this.config.default_mainline);
                         }
                         catch (error) {
                             const message = this.composeMessageForBackportScriptFailure(target, 4, baseref, headref, branchname);
@@ -419,12 +419,17 @@ function checkout(branch, start, pwd) {
     });
 }
 exports.checkout = checkout;
-function cherryPick(commitShas, pwd) {
+function cherryPick(commitShas, pwd, default_mainline) {
     return __awaiter(this, void 0, void 0, function* () {
-        const { exitCode } = yield git("cherry-pick", ["-x", ...commitShas], pwd);
+        const args = ["-x"];
+        if (default_mainline !== undefined) {
+            args.push(`--mainline=${default_mainline}`);
+        }
+        args.push(...commitShas);
+        const { exitCode } = yield git("cherry-pick", args, pwd);
         if (exitCode !== 0) {
             yield git("cherry-pick", ["--abort"], pwd);
-            throw new Error(`'git cherry-pick -x ${commitShas}' failed with exit code ${exitCode}`);
+            throw new Error(`'git cherry-pick ${args.join(" ")}' failed with exit code ${exitCode}`);
         }
     });
 }
@@ -637,6 +642,7 @@ const github_1 = __nccwpck_require__(5928);
  * Is separated from backport for testing purposes
  */
 function run() {
+    var _a;
     return __awaiter(this, void 0, void 0, function* () {
         const token = core.getInput("github_token", { required: true });
         const pwd = core.getInput("github_workspace", { required: true });
@@ -645,14 +651,21 @@ function run() {
         const title = core.getInput("pull_title");
         const copy_labels_pattern = core.getInput("copy_labels_pattern");
         const target_branches = core.getInput("target_branches");
-        const github = new github_1.Github(token);
-        const backport = new backport_1.Backport(github, {
+        const default_mainline = core.getInput("default_mainline");
+        const config = {
             pwd,
             labels: { pattern: pattern === "" ? undefined : new RegExp(pattern) },
             pull: { description, title },
             copy_labels_pattern: copy_labels_pattern === "" ? undefined : new RegExp(copy_labels_pattern),
             target_branches: target_branches === "" ? undefined : target_branches,
-        });
+            default_mainline: default_mainline === "" ? undefined : Number(default_mainline),
+        };
+        // todo: improve config validation
+        if (isNaN((_a = config.default_mainline) !== null && _a !== void 0 ? _a : -1)) {
+            throw new Error(`When defined, \`default_mainline\` must be a number but it was '${default_mainline}''`);
+        }
+        const github = new github_1.Github(token);
+        const backport = new backport_1.Backport(github, config);
         return backport.run();
     });
 }

src/backport.ts

@@ -11,7 +11,7 @@ type PRContent = {
   body: string;
 };
 
-type Config = {
+export type Config = {
   pwd: string;
   labels: {
     pattern?: RegExp;
@@ -22,6 +22,7 @@ type Config = {
   };
   copy_labels_pattern?: RegExp;
   target_branches?: string;
+  default_mainline?: number;
 };
 
 enum Output {
@@ -148,7 +149,11 @@ export class Backport {
           }
 
           try {
-            await git.cherryPick(commitShas, this.config.pwd);
+            await git.cherryPick(
+              commitShas,
+              this.config.pwd,
+              this.config.default_mainline,
+            );
           } catch (error) {
             const message = this.composeMessageForBackportScriptFailure(
               target,

src/git.ts

@@ -67,12 +67,21 @@ export async function checkout(branch: string, start: string, pwd: string) {
   }
 }
 
-export async function cherryPick(commitShas: string[], pwd: string) {
-  const { exitCode } = await git("cherry-pick", ["-x", ...commitShas], pwd);
+export async function cherryPick(
+  commitShas: string[],
+  pwd: string,
+  default_mainline?: number,
+) {
+  const args = ["-x"];
+  if (default_mainline !== undefined) {
+    args.push(`--mainline=${default_mainline}`);
+  }
+  args.push(...commitShas);
+  const { exitCode } = await git("cherry-pick", args, pwd);
   if (exitCode !== 0) {
     await git("cherry-pick", ["--abort"], pwd);
     throw new Error(
-      `'git cherry-pick -x ${commitShas}' failed with exit code ${exitCode}`,
+      `'git cherry-pick ${args.join(" ")}' failed with exit code ${exitCode}`,
     );
   }
 }

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";
 
 /**
@@ -15,17 +15,29 @@ 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 default_mainline = core.getInput("default_mainline");
 
-  const github = new Github(token);
-  const backport = new Backport(github, {
+  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),
-  });
+    default_mainline:
+      default_mainline === "" ? undefined : Number(default_mainline),
+  };
+
+  // todo: improve config validation
+  if (isNaN(config.default_mainline ?? -1)) {
+    throw new Error(
+      `When defined, \`default_mainline\` must be a number but it was '${default_mainline}''`,
+    );
+  }
+
+  const github = new Github(token);
+  const backport = new Backport(github, config);
 
   return backport.run();
 }