feat(pr-url-output): add PULL_REQUEST_URL output variable

This is set to either the generated PR or the one that was found to be already open.

README.md

@@ -28,6 +28,12 @@ What you would like in the body of the pull request.
 
 Default: `sync-branches: New code has just landed in {FROM_BRANCH} so let's bring {TO_BRANCH} up to speed!`
 
+## Outputs
+
+### `PULL_REQUEST_URL`
+
+Set to the URL of either the pull request that was opened by this action or the one that was found to already be open between the two branches.
+
 ## Example usage
 
 ```YML

action.yml

@@ -1,8 +1,8 @@
 name: "Sync branches"
 description: "GitHub Action to, upon successful merge, open a pull request to sync the updated branch back to one or more other branches."
 branding:
-icon: git-pull-request
-color: green
+  icon: git-pull-request
+  color: green
 inputs:
   GITHUB_TOKEN:
     description: "User token to be associated with this pull request."
@@ -19,6 +19,9 @@ inputs:
   PULL_REQUEST_BODY:
     description: "What you would like in the body of the pull request. Default: 'New code has just landed in {fromBranch} so let's bring {toBranch} up to speed!'"
     required: false
+outputs:
+  PULL_REQUEST_URL:
+    description: "URL for either the generated pull request or the currently open one"
 runs:
   using: "node12"
   main: "dist/index.js"

index.js

@@ -43,11 +43,15 @@ async function run() {
       console.log(
         `Pull request successful! You can view it here: ${pullRequest.url}.`
       );
+
+      core.setOutput("PULL_REQUEST_URL", pullRequest.url);
     } else {
       console.log(
         `There is already a pull request to ${toBranch} from ${fromBranch}.`,
         `You can view it here: ${currentPull.url}`
       );
+
+      core.setOutput("PULL_REQUEST_URL", currentPull.url);
     }
   } catch (error) {
     core.setFailed(error.message);