run-tests.sh: determine compose command.

Newer compose is a docker builtin command. Try `docker compose`,
then try `docker-compose`, and if neither is found then exit with an
error.

Currently, the Github Actions "ubuntu-latest" host target sometimes has
the newer form and sometimes does not.

In the workflow, always use `docker compose`.

.github/workflows/push.yml

@@ -17,7 +17,7 @@ jobs:
         run: npm install
 
       - name: compose build of conlink
-        run: docker-compose -f examples/test1-compose.yaml build
+        run: docker compose -f examples/test1-compose.yaml build
 
       - name: "./run-tests.sh"
         timeout-minutes: 5

run-tests.sh

@@ -9,9 +9,16 @@ declare FAIL=0
 
 die() { echo >&2 "${*}"; exit 1; }
 vecho() { [ "${VERBOSE}" ] && echo "${*}" || true; }
-dc() { docker-compose "${@}"; }
+dc() { ${DOCKER_COMPOSE} "${@}"; }
 mdc() { ./mdc "${@}" || die "mdc invocation failed"; }
 
+# Determine compose command
+for dc in "docker compose" "docker-compose"; do
+  ${dc} version 2>/dev/null >&2 && DOCKER_COMPOSE="${dc}" && break
+done
+[ "${DOCKER_COMPOSE}" ] || die "No compose command found"
+echo >&2 "Using compose command '${DOCKER_COMPOSE}'"
+
 dc_init() {
   local cont="${1}" idx="${2}"
   dc down --remove-orphans -t1