Prerelease branch: conventional commits cause version bump instead of rc increment

[omrid-mentee]

Bug Description

When on a prerelease branch, conventional commit messages (e.g., fix:, feat:) cause the version number to bump instead of incrementing the prerelease (rc) number.

Expected Behavior

Given:

• Previous tag: v1.1.1-rc.0
• New commit with message: fix: some bug fix
• Branch is a prerelease branch

Expected new tag: v1.1.1-rc.1 (rc increment)

Actual Behavior

Actual new tag: v1.1.2-rc.0 (patch bump + rc reset)

Root Cause

In src/action.ts, when a conventional commit bump is detected on a prerelease branch:

const releaseType: ReleaseType = isPrerelease
  ? `pre${bump}`   // bump="patch" → "prepatch"
  : bump || defaultBump;

semver.inc("1.1.1-rc.0", "prepatch", "rc") returns 1.1.2-rc.0 — it bumps the patch version and resets the rc counter.

The correct behavior when the previous tag is already a prerelease at the same or higher bump level should be to use prerelease as the release type:

semver.inc("1.1.1-rc.0", "prerelease", "rc") returns 1.1.1-rc.1

The version bump from conventional commits should only be applied on the first prerelease (e.g., going from v1.1.0 release to v1.1.1-rc.0), not on subsequent prereleases where the bump has already been applied.

Configuration

uses: mathieudutour/github-tag-action@v6.2
with:
  github_token: ${{ secrets.TOKEN }}
  default_bump: patch
  default_prerelease_bump: prerelease
  append_to_pre_release_tag: rc
  release_branches: master,main,develop
  pre_release_branches: .*

Suggested Fix

When on a prerelease branch, check if the previous tag is already a prerelease with the same or higher version bump applied. If so, use prerelease instead of pre${bump}:

if (isPrerelease && previousVersion.prerelease.length > 0) {
  // Already on a prerelease — just increment the rc number
  releaseType = 'prerelease';
} else {
  releaseType = isPrerelease ? `pre${bump}` : bump || defaultBump;
}

Related Issues

• Prerelease not incrementing #88 — same underlying problem
• Support for incrementing the prerelease number when no automatic bumps are encountered. #102 — fixed the no-bump case but not the conventional-commit-bump case