fix(release-changelog): handle missing bootstrap previous version

Author: jobcespedes

release/changelog/README.md

@@ -4,6 +4,8 @@ Generates a release changelog with `git-cliff` and stages the output file.
 
 Use this action in release workflows that need a changelog file, a step summary, and an optional artifact generated from the commit range between the previous version and the new version.
 
+When `previous-version` is `0.0.0` and that ref does not exist, the action treats the release as the initial changelog generation. It warns in the workflow log, generates from `HEAD` so the first commit is included, and disables prepend mode for that run.
+
 ```yaml
 steps:
   - uses: actions/checkout@v6

release/changelog/action.yml

@@ -109,16 +109,24 @@ runs:
         git-cliff --version
 
         echo "Setting up git-cliff context..."
+        initial_release_without_previous_ref="false"
+        if [ "${PREVIOUS_VERSION}" = "0.0.0" ] && ! git rev-parse --verify --quiet "${PREVIOUS_VERSION}^{commit}" >/dev/null; then
+          initial_release_without_previous_ref="true"
+          echo "::warning title=Release changelog::Previous version 0.0.0 does not exist; generating the initial changelog from HEAD and disabling prepend."
+        fi
+
         output="${CHANGELOG_OUTPUT}"
-        if [ "${PREPEND}" = "true" ]; then
+        if [ "${PREPEND}" = "true" ] && [ "${initial_release_without_previous_ref}" != "true" ]; then
           output="${RUNNER_TEMP}/cliff/changelog/${CHANGELOG_OUTPUT}"
           mkdir -p "$(dirname "${output}")"
           [ -f "${output}" ] || touch "${output}"
         fi
 
         range="${PREVIOUS_VERSION}..${VERSION}"
         prepend_args=()
-        if [ "${PREPEND}" = "true" ]; then
+        if [ "${initial_release_without_previous_ref}" = "true" ]; then
+          range="HEAD"
+        elif [ "${PREPEND}" = "true" ]; then
           range="${PREVIOUS_VERSION}..HEAD"
           prepend_args=(--prepend "${CHANGELOG_OUTPUT}")
         fi