Update build.sh to work with GIT_HEAD

build.sh

@@ -1,4 +1,23 @@
-TAG=$(git rev-parse --short HEAD)$(test -n "$(git status --porcelain)" && echo -dirty)
-REPO=quay.io/quay/quay:$TAG
+#!/usr/bin/env bash
+
+set -e
+
+if [[ -n "$(git status --porcelain)" ]]; then
+  echo 'dirty build not supported' >&2
+  exit 1
+fi
+
+# get named head (ex: branch, tag, etc..)
+NAME="$( git rev-parse --abbrev-ref HEAD )"
+
+# get 7-character sha
+SHA=$( git rev-parse --short HEAD )
+
+# checkout commit so .git/HEAD points to full sha (used in Dockerfile)
+git checkout $SHA
+
+REPO=quay.io/quay/quay:$SHA
 docker build -t $REPO .
 echo $REPO
+
+git checkout "$NAME"