feat: disable label_pattern with empty string

In order to only use the `target_branches` input, it can be useful to
completely disable the `label_pattern` input.

This adds the ability to completely disable determining the target
branches based on labels. Simply set the `label_pattern` input to an
empty string `''`.

README.md

@@ -134,6 +134,7 @@ Default: `^backport ([^ ]+)$` (e.g. matches `backport release-3.4`)
 
 Regex pattern to match the backport labels on the merged pull request.
 Must contain a capture group for the target branch.
+Label matching can be disabled entirely using an empty string `''` as pattern.
 
 The action will backport the pull request to each matched target branch.
 See [How it works](#how-it-works).

src/backport.ts

@@ -14,7 +14,7 @@ type PRContent = {
 type Config = {
   pwd: string;
   labels: {
-    pattern: RegExp;
+    pattern?: RegExp;
   };
   pull: {
     description: string;
@@ -62,7 +62,7 @@ export class Backport {
       const target_branches = this.findTargetBranches(mainpr, this.config);
       if (target_branches.length === 0) {
         console.log(
-          `Nothing to backport: no 'target_branches' specified and none of the labels match the backport pattern '${this.config.labels.pattern.source}'`
+          `Nothing to backport: no 'target_branches' specified and none of the labels match the backport pattern '${this.config.labels.pattern?.source}'`
         );
         return; // nothing left to do here
       }
@@ -91,7 +91,8 @@ export class Backport {
           .filter(
             (label) =>
               label.match(copyLabelsPattern) &&
-              !label.match(this.config.labels.pattern)
+              (this.config.labels.pattern === undefined ||
+                !label.match(this.config.labels.pattern))
           );
       }
       console.log(
@@ -386,21 +387,22 @@ function findTargetBranchesFromLabels(
   labels: string[],
   config: Pick<Config, "labels">
 ) {
-  if (config.labels.pattern.source === new RegExp("").source) {
+  const pattern = config.labels.pattern;
+  if (pattern === undefined) {
     return [];
   }
   return labels
     .map((label) => {
-      return { label: label, match: config.labels.pattern.exec(label) };
+      return { label: label, match: pattern.exec(label) };
     })
     .filter((result) => {
       if (!result.match) {
         console.log(
-          `label '${result.label}' doesn't match \`label_pattern\` '${config.labels.pattern.source}'`
+          `label '${result.label}' doesn't match \`label_pattern\` '${pattern.source}'`
         );
       } else if (result.match.length < 2) {
         console.error(
-          dedent`label '${result.label}' matches \`label_pattern\` '${config.labels.pattern.source}', \
+          dedent`label '${result.label}' matches \`label_pattern\` '${pattern.source}', \
           but no branchname could be captured. Please make sure to provide a regex with a capture group as \
           \`label_pattern\`.`
         );

src/main.ts

@@ -10,7 +10,7 @@ import { Github } from "./github";
 async function run(): Promise<void> {
   const token = core.getInput("github_token", { required: true });
   const pwd = core.getInput("github_workspace", { required: true });
-  const pattern = new RegExp(core.getInput("label_pattern"));
+  const pattern = core.getInput("label_pattern");
   const description = core.getInput("pull_description");
   const title = core.getInput("pull_title");
   const copy_labels_pattern = core.getInput("copy_labels_pattern");
@@ -19,7 +19,7 @@ async function run(): Promise<void> {
   const github = new Github(token);
   const backport = new Backport(github, {
     pwd,
-    labels: { pattern },
+    labels: { pattern: pattern === "" ? undefined : new RegExp(pattern) },
     pull: { description, title },
     copy_labels_pattern:
       copy_labels_pattern === "" ? undefined : new RegExp(copy_labels_pattern),

src/test/backport.test.ts

@@ -26,13 +26,15 @@ describe("find target branches", () => {
 
     it("when a label matches the pattern but doesn't capture a target branch", () => {
       expect(
-        findTargetBranches({ labels: { pattern: /^no capture group$/ } }, ["no capture group"])
+        findTargetBranches({ labels: { pattern: /^no capture group$/ } }, [
+          "no capture group",
+        ])
       ).toEqual([]);
     });
 
     it("when the label pattern is an empty string", () => {
       expect(
-        findTargetBranches({ labels: { pattern: new RegExp("") } }, [
+        findTargetBranches({ labels: { pattern: undefined } }, [
           "an empty string",
         ])
       ).toEqual([]);