🌱 add Go directive check as Makefile target

Makefile

@@ -25,6 +25,7 @@ SHELL:=/usr/bin/env bash
 #
 GO_VERSION ?= 1.21.9
 GO_CONTAINER_IMAGE ?= docker.io/library/golang:$(GO_VERSION)
+GO_DIRECTIVE_VERSION ?= 1.21.0
 
 # Use GOPROXY environment variable if set
 GOPROXY := $(shell go env GOPROXY)
@@ -424,11 +425,15 @@ APIDIFF_OLD_COMMIT ?= $(shell git rev-parse origin/main)
 apidiff: $(GO_APIDIFF) ## Check for API differences
 	$(GO_APIDIFF) $(APIDIFF_OLD_COMMIT) --print-compatible
 
-ALL_VERIFY_CHECKS = licenses boilerplate shellcheck modules gen conversions doctoc flavors import-restrictions
+ALL_VERIFY_CHECKS = licenses boilerplate shellcheck modules gen conversions doctoc flavors import-restrictions go-directive
 
 .PHONY: verify
 verify: $(addprefix verify-,$(ALL_VERIFY_CHECKS)) ## Run all verify-* targets
 
+.PHONY: verify-go-directive
+verify-go-directive:
+	TRACE=$(TRACE) ./hack/verify-go-directive.sh -g $(GO_DIRECTIVE_VERSION)
+
 .PHONY: verify-modules
 verify-modules: generate-modules  ## Verify go modules are up to date
 	@if !(git diff --quiet HEAD -- go.sum go.mod $(TEST_DIR)/go.mod $(TEST_DIR)/go.sum); then \

hack/verify-go-directive.sh

@@ -0,0 +1,77 @@
+#!/usr/bin/env bash
+
+# Copyright 2024 The Kubernetes Authors.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+set -o errexit
+set -o nounset
+set -o pipefail
+
+if [[ "${TRACE-0}" == "1" ]]; then
+    set -o xtrace
+fi
+
+function usage {
+  local script
+  script="$(basename "$0")"
+
+  cat >&2 <<EOF
+Usage: ${script} [-g <maximum go directive>]
+This script should be run at the root of a module.
+-g <maximum go directive>
+  Compare the go directive in the local working copy's go.mod
+  to the specified maximum version it can be. Versions provided
+  here are of the form 1.x.y, without the 'go' prefix.
+Examples:
+  ${script} -g 1.21.10
+EOF
+  exit 1
+}
+
+max=""
+while getopts g: opt
+do case "$opt" in
+  g)    max="$OPTARG";;
+  [?])  usage;;
+  esac
+done
+
+# If max is empty, print usage
+if [[ -z "${max}" ]]; then
+  usage;
+fi
+
+# If go directive is not specified as 1.x.y, print usage
+if [[ ! "${max}" =~ ^1(\.[0-9]+){2}$ ]]; then
+  usage;
+fi
+
+dir=""
+if [[ -z "${dir}" ]]; then
+  dir="."
+fi
+
+find "${dir}" -name "go.mod" -type f -print0 | while IFS= read -r -d '' file; do
+  echo "Running go directive verify test for ${file} against ${max}"
+  current=$(grep '^go [1-9]*' go.mod | cut -d ' ' -f2)
+  if [[ -z "${current}" ]]; then
+    echo >&2 "FAIL: could not get value of Go directive from ${file}"
+    exit 1
+  fi
+
+  if ! printf '%s\n' "${current}" "${max}" | sort --check=silent --version-sort; then
+    echo >&2 "FAIL: current Go directive ${current} is greater than ${max}"
+    exit 1
+  fi
+done