Add initial jq-based templating engine

Author: tianon

.gitattributes

@@ -0,0 +1,3 @@
+**/Dockerfile            linguist-generated
+**/docker-entrypoint.sh  linguist-generated
+Dockerfile.template      linguist-language=Dockerfile

.github/workflows/verify-templating.yml

@@ -0,0 +1,22 @@
+name: Verify Templating
+
+on:
+  pull_request:
+  push:
+
+defaults:
+  run:
+    shell: 'bash -Eeuo pipefail -x {0}'
+
+jobs:
+  apply-templates:
+    name: Check For Uncomitted Changes
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+      - name: Apply Templates
+        run: ./apply-templates.sh
+      - name: Check Git Status
+        run: |
+          status="$(git status --short)"
+          [ -z "$status" ]

.gitignore

@@ -0,0 +1 @@
+.jq-template.awk

2.1/Dockerfile

@@ -1,4 +1,4 @@
-FROM adoptopenjdk:%%JAVA_VERSION%%-jre-hotspot-bionic
+FROM adoptopenjdk:{{ .java }}-jre-hotspot-bionic
 
 # explicitly set user/group IDs
 RUN set -eux; \
@@ -13,7 +13,15 @@ RUN set -eux; \
 # "free" is used by cassandra-env.sh
 		procps \
 # "cqlsh" needs a python interpreter
+{{
+	# python3 is only supported in 4.0+
+	# https://issues.apache.org/jira/browse/CASSANDRA-10190
+	if env.version | split(".") | .[0] | tonumber < 4 then (
+-}}
+		python \
+{{ ) else ( -}}
 		python3 \
+{{ ) end -}}
 # "ip" is not required by Cassandra itself, but is commonly used in scripting Cassandra's configuration (since it is so fixated on explicit IP addresses)
 		iproute2 \
 # Cassandra will automatically use numactl if available
@@ -59,8 +67,8 @@ ENV GPG_KEYS \
 # gpg: key E91335D77E3E87CB: public key "Michael Semb Wever <[email protected]>" imported
 	A4C465FEA0C552561A392A61E91335D77E3E87CB
 
-ENV CASSANDRA_VERSION %%CASSANDRA_VERSION%%
-ENV CASSANDRA_SHA512 %%CASSANDRA_SHA512%%
+ENV CASSANDRA_VERSION {{ .version }}
+ENV CASSANDRA_SHA512 {{ .sha512 }}
 
 RUN set -eux; \
 	savedAptMark="$(apt-mark showmanual)"; \
@@ -142,7 +150,9 @@ RUN set -eux; \
 VOLUME /var/lib/cassandra
 
 COPY docker-entrypoint.sh /usr/local/bin/
+{{ if env.version | split(".") | .[0] | tonumber < 4 then ( -}}
 RUN ln -s usr/local/bin/docker-entrypoint.sh /docker-entrypoint.sh # backwards compat
+{{ ) else "" end -}}
 ENTRYPOINT ["docker-entrypoint.sh"]
 
 # 7000: intra-node communication

2.2/Dockerfile

@@ -0,0 +1,40 @@
+#!/usr/bin/env bash
+set -Eeuo pipefail
+
+[ -f versions.json ] # run "versions.sh" first
+
+jqt='.jq-template.awk'
+if [ -n "${BASHBREW_SCRIPTS:-}" ]; then
+	jqt="$BASHBREW_SCRIPTS/jq-template.awk"
+elif [ "$BASH_SOURCE" -nt "$jqt" ]; then
+	wget -qO "$jqt" 'https://github.com/docker-library/bashbrew/raw/ac3e8e9541cb362a579b05bec41dd40d1df1c6e6/scripts/jq-template.awk'
+fi
+
+if [ "$#" -eq 0 ]; then
+	versions="$(jq -r 'keys | map(@sh) | join(" ")' versions.json)"
+	eval "set -- $versions"
+fi
+
+generated_warning() {
+	cat <<-EOH
+		#
+		# NOTE: THIS DOCKERFILE IS GENERATED VIA "apply-templates.sh"
+		#
+		# PLEASE DO NOT EDIT IT DIRECTLY.
+		#
+
+	EOH
+}
+
+for version; do
+	export version
+
+	echo "processing $version ..."
+
+	{
+		generated_warning
+		gawk -f "$jqt" Dockerfile.template
+	} > "$version/Dockerfile"
+
+	cp -a docker-entrypoint.sh "$version/"
+done