create make target ensuring unique version

Makefile

@@ -31,7 +31,10 @@ fmtcheck:
 	test -z $(shell go fmt $(SOURCE))
 .PHONY: fmtcheck
 
-tag:
+check-tag:
+	./scripts/ensure-unique-version.sh "$(VERSION)"
+
+tag: check-tag
 	echo "creating git tag $(VERSION)"
 	git tag $(VERSION)
 	git push origin $(VERSION)

scripts/ensure-unique-version.sh

@@ -0,0 +1,17 @@
+#!/bin/sh
+
+version="${1}"
+repo="mdb/gh-dispatch"
+
+result="$(curl \
+  --header "Accept: application/vnd.github.v3+json" \
+  --write "%{http_code}" \
+  --out "/dev/null" \
+  "https://api.github.com/repos/${repo}/releases/tags/${version}")"
+
+if [ "${result}" = "404" ]; then
+  exit 0
+fi
+
+echo "${version} is an existing ${repo} release"
+exit 1