feat: add source-dir and repo-url inputs for external repo support

Allow changelog generation from upstream repositories instead of only
the current working directory. Supports packaging repos that contain
only rpm spec files while the source lives in an external git repo.

- source-dir: point at an existing local checkout
- repo-url: action clones a bare copy automatically
- source-dir takes precedence if both are set

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

scripts/generate-rpm-changelog.sh

@@ -9,6 +9,12 @@
 #   RELEASE           — release suffix, default "1"
 #   TAG_PATTERN       — glob for release tags, default "v*"
 #   EXCLUDE_PATTERNS  — newline-separated grep -E patterns to drop
+#   SOURCE_DIR        — path to an external git checkout to read history from
+#   REPO_URL          — URL of a remote repo to clone (bare) for history
+#
+# If SOURCE_DIR or REPO_URL is set, commits are collected from that
+# repository instead of the current working directory. SOURCE_DIR
+# takes precedence over REPO_URL.
 #
 # Collects commits since the previous matching tag, drops filtered
 # lines (bump-version chore commits, merges, etc.), and writes a
@@ -22,6 +28,35 @@ AUTHOR="${CHANGELOG_AUTHOR:-Gitea Actions <actions@git.lair.cafe>}"
 RELEASE="${RELEASE:-1}"
 TAG_PATTERN="${TAG_PATTERN:-v*}"
 EXCLUDE_PATTERNS="${EXCLUDE_PATTERNS:-$'^- chore: bump version\n^- Merge'}"
+SOURCE_DIR="${SOURCE_DIR:-}"
+REPO_URL="${REPO_URL:-}"
+
+# Resolve the git directory to collect commits from.
+# Priority: SOURCE_DIR > REPO_URL > current working directory.
+CLEANUP_DIR=""
+GIT_ARGS=()
+
+if [ -n "$SOURCE_DIR" ]; then
+  if [ ! -d "$SOURCE_DIR/.git" ] && ! git -C "$SOURCE_DIR" rev-parse --git-dir >/dev/null 2>&1; then
+    printf 'error: source-dir is not a git repository: %s\n' "$SOURCE_DIR" >&2
+    exit 1
+  fi
+  GIT_ARGS=(-C "$SOURCE_DIR")
+  printf 'Using source-dir for commit history: %s\n' "$SOURCE_DIR"
+elif [ -n "$REPO_URL" ]; then
+  CLONE_DIR=$(mktemp -d)
+  CLEANUP_DIR="$CLONE_DIR"
+  printf 'Cloning %s (bare) for commit history…\n' "$REPO_URL"
+  git clone --bare --filter=blob:none "$REPO_URL" "$CLONE_DIR/repo.git"
+  GIT_ARGS=(-C "$CLONE_DIR/repo.git")
+fi
+
+cleanup() {
+  if [ -n "$CLEANUP_DIR" ] && [ -d "$CLEANUP_DIR" ]; then
+    rm -rf "$CLEANUP_DIR"
+  fi
+}
+trap cleanup EXIT
 
 if [ ! -f "$SPEC" ]; then
   echo "error: spec file not found: $SPEC" >&2
@@ -34,10 +69,10 @@ if ! grep -q '^%changelog' "$SPEC"; then
 fi
 
 # Find the previous release tag (exclude the current tag at HEAD).
-PREV_TAG=$(git describe --tags --abbrev=0 --match="$TAG_PATTERN" HEAD^ 2>/dev/null || echo "")
+PREV_TAG=$(git "${GIT_ARGS[@]}" describe --tags --abbrev=0 --match="$TAG_PATTERN" HEAD^ 2>/dev/null || echo "")
 
 if [ -n "$PREV_TAG" ]; then
-  RAW=$(git log --no-merges --pretty=format:'- %s' "${PREV_TAG}..HEAD")
+  RAW=$(git "${GIT_ARGS[@]}" log --no-merges --pretty=format:'- %s' "${PREV_TAG}..HEAD")
 
   # Build a combined grep -E pattern from the exclude list; drop blanks.
   COMBINED=""