scripts/prepare-release: patch golang version in Makefile

Make it mandatory to specify a golang version with "-g" when running the
script (and patching repo content). The given version will be patched
into the Makefile to fix the version used in the release build - it is
meant to use a exact point release (like 1.18.3) to get reproducible
builds.

scripts/prepare-release.sh

@@ -5,12 +5,14 @@ this=`basename $0`
 
 usage () {
 cat << EOF
-Usage: $this [-h] [-a] [-b] [-k GPG_KEY] RELEASE_VERSION
+Usage: $this [-h] [-b] [-k GPG_KEY] {-a|-g GOLANG_VERSION} RELEASE_VERSION
 
 Options:
   -h         show this help and exit
   -a         do not patch files in the repo
   -b         do not generate assets
+  -g         golang version to fix for the release (mandatory when -a not
+             specified). Should be a exact point release e.g. 1.18.3.
   -k         gpg key to use for signing the assets
 
 Example:
@@ -39,12 +41,14 @@ files:
 #
 no_patching=
 no_assets=
-while getopts "abk:h" opt; do
+while getopts "abg:k:h" opt; do
     case $opt in
         a)  no_patching=y
             ;;
         b)  no_assets=y
             ;;
+        g) golang_version="$OPTARG"
+            ;;
         k) signing_key="$OPTARG"
             ;;
         h)  usage
@@ -68,6 +72,12 @@ if [ $# -ne 1 ]; then
     exit 1
 fi
 
+if [ -z "$no_patching" -a -z "$golang_version" ]; then
+    echo -e "ERROR: '-g GOLANG_VERSION' must be specified when modifying repo (i.e. when '-a' is not used)\n"
+    usage
+    exit 1
+fi
+
 release=$1
 shift 1
 
@@ -94,6 +104,11 @@ fi
 # Modify files in the repo to point to new release
 #
 if [ -z "$no_patching" ]; then
+    # Patch docs configuration
+    echo Patching golang version $golang_version into Makefile
+    sed -e s"/\(^BUILDER_IMAGE.*=.*golang:\)[0-9][0-9.]*\(.*\)/\1$golang_version\2/" \
+        -i Makefile
+
     # Patch docs configuration
     echo Patching docs/_config.yml
     sed -e s"/release:.*/release: $release/"  \