build-release: fix VERSION build-arg and add --no-push for the docker target

Pass the computed VERSION as a build-arg, mirroring the docker-release workflow. Without it the container's VERSION is set-but-empty, `VERSION ?=` in the Makefile won't overwrite it, the git-describe fallback never runs, and `make install-program` fails with "git is required for generating version information".

Also add --no-push, so a release captain can do a full test build without publishing elementsproject/lightningd:$VERSION and :latest (the target always runs `docker buildx build --push`, since multi-arch images cannot be --load'ed into the classic docker store). The build only populates the builder's cache; a subsequent run without the flag pushes from cache quickly.

Co-Authored-By: Claude <claude@users.noreply.github.com>

Author: 2 people

tools/build-release.sh

@@ -31,6 +31,7 @@ fi
 FORCE_UNCLEAN=false
 VERIFY_RELEASE=false
 WITHOUT_ZIP=false
+NO_PUSH=false
 SUDO=
 
 ALL_TARGETS="bin-Fedora bin-Ubuntu docker sign"
@@ -63,11 +64,14 @@ while [ $# -gt 0 ]; do
         --without-zip)
             WITHOUT_ZIP=true
             ;;
+        --no-push)
+            NO_PUSH=true
+            ;;
         --sudo)
             SUDO=sudo
             ;;
         --help)
-            echo "Usage: [--force-version=<ver>] [--force-unclean] [--force-mtime=YYYY-MM-DD] [--verify] [TARGETS]"
+            echo "Usage: [--force-version=<ver>] [--force-unclean] [--force-mtime=YYYY-MM-DD] [--verify] [--no-push] [TARGETS]"
             echo Known targets: "$ALL_TARGETS"
             echo "Example: tools/build-release.sh"
             echo "Example: tools/build-release.sh --force-version=v23.05 --force-unclean --force-mtime=2023-05-01 bin-Fedora bin-Ubuntu sign"
@@ -213,9 +217,14 @@ if [ -z "${TARGETS##* docker *}" ] || [ -z "${TARGETS##* docker}" ]; then
     echo "Building Docker Images"
     DOCKER_USER="elementsproject"
     echo "Creating multi-platform images tagged as $VERSION and latest"
-    # --load does not work with multiarch. Only --push works.
-    # ERROR: docker exporter does not currently support exporting manifest lists
-    DOCKER_OPTS="--push --platform linux/amd64,linux/arm64,linux/arm/v7"
+    if $NO_PUSH; then
+        # Build without publishing: the result only populates the builder's
+        # cache, so a later run without --no-push pushes from cache quickly.
+        DOCKER_OPTS="--platform linux/amd64,linux/arm64,linux/arm/v7"
+    else
+        DOCKER_OPTS="--push --platform linux/amd64,linux/arm64,linux/arm/v7"
+    fi
+    DOCKER_OPTS="$DOCKER_OPTS --build-arg VERSION=$VERSION"
     DOCKER_OPTS="$DOCKER_OPTS -t $DOCKER_USER/lightningd:$VERSION"
     DOCKER_OPTS="$DOCKER_OPTS -t $DOCKER_USER/lightningd:latest"
     DOCKER_OPTS="$DOCKER_OPTS --cache-to=type=local,dest=/tmp/docker-cache --cache-from=type=local,src=/tmp/docker-cache"
@@ -227,7 +236,11 @@ if [ -z "${TARGETS##* docker *}" ] || [ -z "${TARGETS##* docker}" ]; then
     fi
     # shellcheck disable=SC2086
     $SUDO docker buildx build $DOCKER_OPTS .
-    echo "Pushed multi-platform images tagged as $VERSION and latest"
+    if $NO_PUSH; then
+        echo "Built multi-platform images without pushing (rerun without --no-push to publish)"
+    else
+        echo "Pushed multi-platform images tagged as $VERSION and latest"
+    fi
 fi
 
 if [ -z "${TARGETS##* sign *}" ] || [ -z "${TARGETS##* sign}" ]; then