Automate FBC upgrade graph flow

During publish of the operator to OperatorHub, "PREVIOUS_VERSION"
variable is used to configure upgrade path for FBC.
Currently, this variable is maintainer manually and in case of missing
update to the relevant version, leads to a gate job failure.

Automate "PREVIOUS_VERSION" variable detection, based on the "VERSION"
variable, which is updated as part of the release flow and based on "git
tag" detection to catch the latest released version.

Signed-off-by: Maxim Babushkin <mbabushk@redhat.com>

Author: MaxBab

Makefile.core.mk

@@ -22,15 +22,25 @@ OLD_VARS := $(.VARIABLES)
 VERSION ?= 1.30.0
 MINOR_VERSION := $(shell echo "${VERSION}" | cut -f1,2 -d'.')
 
-# This version will be used to generate the OLM upgrade graph in the FBC as a version to be replaced by the new operator version defined in $VERSION.
-# This applies for stable releases, for nightly releases we are getting previous version directly from the FBC.
+# Auto-detect PREVIOUS_VERSION from git tags relative to VERSION
+# This is used to generate the OLM upgrade graph in FBC for stable releases.
+# For nightly releases, the previous version is fetched directly from the FBC catalog.
+#
+# The VERSION variable should be updated to the new release version before running bundle-publish.
+# The query will find the latest existing tag less than VERSION (e.g., VERSION=1.31.0 → finds 1.30.0).
+#
 # Currently we are pushing the operator to two operator hubs https://github.com/k8s-operatorhub/community-operators and
 # https://github.com/redhat-openshift-ecosystem/community-operators-prod. Nightly builds go only to community-operators-prod which already
-# supports FBC. FBC yaml files and kept in community-operators-prod repo and we only generate a PR with changes using make targets from this Makefile.
+# supports FBC. FBC yaml files are kept in community-operators-prod repo and we only generate a PR with changes using make targets from this Makefile.
 # There are also GH workflows defined to release nightly and stable operators.
 # There is no need to define `replaces` and `skipRange` fields in the CSV as those fields are defined in the FBC and CSV values are ignored.
 # FBC is source of truth for OLM upgrade graph.
-PREVIOUS_VERSION ?= 1.29.1
+#
+# To override: make bundle-publish -e PREVIOUS_VERSION=X.Y.Z
+#
+PREVIOUS_VERSION ?= $(shell \
+	MAJOR=$$(echo "$(VERSION)" | cut -f1 -d'.'); \
+	git tag --list "$${MAJOR}.*.*" 2>/dev/null | sort -V | awk -v ver="$(VERSION)" '$$0 < ver {latest=$$0} END {print latest}')
 
 OPERATOR_NAME ?= sailoperator
 VERSIONS_YAML_DIR ?= pkg/istioversion

hack/operatorhub/publish-bundle.sh

@@ -32,6 +32,47 @@ GIT_CONFIG_USER_EMAIL="${GIT_CONFIG_USER_EMAIL:-}"
 : "${CHANNELS:?"Missing CHANNELS variable"}"
 : "${PREVIOUS_VERSION:?"Missing PREVIOUS_VERSION variable"}"
 
+# Validate PREVIOUS_VERSION is a valid semantic version
+if ! validate_semantic_versioning "v${PREVIOUS_VERSION}" 2>/dev/null; then
+  echo "ERROR: PREVIOUS_VERSION (${PREVIOUS_VERSION}) is not a valid semantic version" >&2
+  exit 1
+fi
+
+# Validate PREVIOUS_VERSION exists as git tag
+if [[ ${OPERATOR_VERSION} != *"nightly"* ]]; then
+  # Check if PREVIOUS_VERSION is empty (git tag query failed)
+  if [ -z "${PREVIOUS_VERSION}" ]; then
+    echo "ERROR: PREVIOUS_VERSION is empty!" >&2
+    echo "  This indicates git tag query failed to find a suitable previous version" >&2
+    echo "  Possible causes:" >&2
+    echo "    - No git tags exist for this major version" >&2
+    echo "    - Git repository is not available" >&2
+    echo "    - VERSION in Makefile is incorrect" >&2
+    echo "  Please verify VERSION is set correctly and git tags exist" >&2
+    echo "  Or explicitly set: make bundle-publish -e PREVIOUS_VERSION=X.Y.Z" >&2
+    exit 1
+  fi
+
+  if git rev-parse --git-dir > /dev/null 2>&1; then
+    if ! git tag --list | grep -q "^${PREVIOUS_VERSION}$"; then
+      echo "WARNING: PREVIOUS_VERSION (${PREVIOUS_VERSION}) does not exist as a git tag!" >&2
+      echo "  This may indicate the version detection failed or an override was used" >&2
+      echo "  Available recent tags:" >&2
+      git tag --list | grep -E '^[0-9]+\.[0-9]+\.[0-9]+$' | sort -V | tail -5 >&2
+
+      # In CI, this is an error
+      if [ "${CI:-false}" = "true" ]; then
+        echo "ERROR: PREVIOUS_VERSION must be a valid git tag in CI mode" >&2
+        exit 1
+      fi
+    else
+      echo "Verified: PREVIOUS_VERSION tag exists in git repository ✓"
+    fi
+  fi
+fi
+
+echo "Using PREVIOUS_VERSION: ${PREVIOUS_VERSION} for OLM upgrade graph"
+
 show_help() {
   echo "publish-bundle - raises PR to Operator Hub"
   echo " "