feat: fallback to default branch (#68)

README.md

@@ -62,7 +62,7 @@ ignore-team-members | true | Whether to ignore in the case that the PR author is
 body-regex | `(fix\|resolv\|clos)(e)*(s\|d)* #\d+` | Regular expression to identify whether the PR body refers to an issue[^2].
 body-auto-close | true | Whether or not to auto-close on failed check of PR Body
 body-comment | (see [action.yml](./action.yml)) | Comment to leave on PR on failed check of PR Body
-protected-branch | "main" | Branch that check should ensure that PR does not use as it's head.
+protected-branch | (Blank) | Branch that check should ensure that PR does not use as it's head. If left blank, it falls back to default branch.
 protected-branch-auto-close | true | Whether or not to auto-close on failed check of PR head branch
 protected-branch-comment | (see [action.yml](./action.yml)) | Comment to leave on PR on failed check of PR head branch.
 title-check-enable | true | Whether or not to lint PR title per [conventional commits](https://www.conventionalcommits.org/en/v1.0.0/).

src/main.ts

@@ -10,7 +10,7 @@ const baseComment = core.getInput('base-comment')
 const bodyRegexInput = core.getInput('body-regex')
 const bodyAutoClose = core.getBooleanInput('body-auto-close')
 const bodyComment = core.getInput('body-comment')
-const protectedBranch = core.getInput('protected-branch')
+let protectedBranch = core.getInput('protected-branch')
 const protectedBranchAutoClose = core.getBooleanInput(
   'protected-branch-auto-close'
 )
@@ -26,6 +26,8 @@ async function run(): Promise<void> {
     const pr = ctx.issue
     const isDraft = (ctx.payload.pull_request?.draft ?? false) === true
     const repoOwner = context.repo.owner
+    if (protectedBranch === '')
+      protectedBranch = ctx.payload.repository?.default_branch ?? ''
     const isClosed =
       (ctx.payload.pull_request?.state ?? 'open').toLowerCase() === 'closed'
     if (isClosed) {