Allow deploying latest build again (#114)

The current deployable check does not allow to redeploy the same
deployment once again. Meaning if your deployment gets corrupted
somehow you cannot delete it and deploy it again.

As an example, Airflow (jobflow) currently as a bug due to missing
support for certain kubernetes resources which can have it looses
track of some of the resources it created in k8s. The only work
around seem to delete and create again the deployment (_cf._
apache/airflow#21087).

orbs/helm-runner/deployable

@@ -0,0 +1,53 @@
+#!/usr/bin/env sh
+
+set -eu
+
+fatal() {
+    printf "$*\n" >/dev/stderr
+    exit 1
+}
+
+usage() {
+    cat <<EOF
+usage: $0 OPTIONS <name>
+
+OPTIONS
+
+-h display help
+-p tag pattern (default: $pattern)
+EOF
+}
+
+pattern="*"
+
+OPTIND=1
+while getopts 'hp:' arg; do
+    case "$arg" in
+	h) usage; exit 0 ;;
+	p) pattern="$OPTARG" ;;
+	?) fatal "unknown option" ;;
+    esac
+done
+shift $((OPTIND - 1))
+
+if [ ! -d ".git" ]; then
+    fatal "no git repository found"
+fi
+
+last_tag=$(git tag --sort version:refname --list "$pattern" | tail -1)
+# There are no tags at all
+if [ -z "$last_tag" ]; then
+    exit 0
+fi
+
+deployed_sha1=$(git rev-parse "$last_tag")
+current_sha1=$(git rev-parse HEAD)
+
+# List commits behind the latest deployment tag, to see if the current commit is not behind.
+# Exclude the tagged commit itself so we can redeploy an already deployed, and thus tagged,
+# commit.
+# Why isn't it enough to check that "${deployed_sha1}" != "${current_sha1}"?
+if { git rev-list "^${deployed_sha1}" | grep -q "${current_sha1}" ; }
+then
+    fatal "the current build is older than the deployed one"
+fi

orbs/helm/deployable

@@ -35,13 +35,19 @@ if [ ! -d ".git" ]; then
 fi
 
 last_tag=$(git tag --sort version:refname --list "$pattern" | tail -1)
+# There are no tags at all
 if [ -z "$last_tag" ]; then
     exit 0
 fi
 
 deployed_sha1=$(git rev-parse "$last_tag")
 current_sha1=$(git rev-parse HEAD)
 
-if [ "$(git rev-list $deployed_sha1 | grep $current_sha1)" ]; then
+# List commits behind the latest deployment tag, to see if the current commit is not behind.
+# Exclude the tagged commit itself so we can redeploy an already deployed, and thus tagged,
+# commit.
+# Why isn't it enough to check that "${deployed_sha1}" != "${current_sha1}"?
+if { git rev-list "^${deployed_sha1}" | grep -q "${current_sha1}" ; }
+then
     fatal "the current build is older than the deployed one"
 fi