Docs: how to build in docker + features support (#643)

1. Explain how to build `bb` for linux using docker.
2. Add support for setting the various `BABASHKA_FEATURE_*`
   when doing docker build via `--build-arg`.

Dockerfile

@@ -1,5 +1,4 @@
 FROM clojure:lein-2.9.1 AS BASE
-ARG BABASHKA_XMX="-J-Xmx3g"
 
 RUN apt update
 RUN apt install --no-install-recommends -yy curl unzip build-essential zlib1g-dev
@@ -7,11 +6,48 @@ WORKDIR "/opt"
 RUN curl -sLO https://github.com/graalvm/graalvm-ce-builds/releases/download/vm-20.2.0/graalvm-ce-java11-linux-amd64-20.2.0.tar.gz
 RUN tar -xzf graalvm-ce-java11-linux-amd64-20.2.0.tar.gz
 
+ARG BABASHKA_XMX="-J-Xmx3g"
+
 ENV GRAALVM_HOME="/opt/graalvm-ce-java11-20.2.0"
 ENV JAVA_HOME="/opt/graalvm-ce-java11-20.2.0/bin"
 ENV PATH="$JAVA_HOME:$PATH"
 ENV BABASHKA_XMX=$BABASHKA_XMX
 
+# Make it possible to use Docker to build bb with a particular set of features
+# by setting them at build time via `docker build --build-arg ARG_NAME=true ...`
+ARG BABASHKA_LEAN=
+ARG BABASHKA_FEATURE_CORE_ASYNC=
+ARG BABASHKA_FEATURE_CSV=
+ARG BABASHKA_FEATURE_JAVA_NIO=
+ARG BABASHKA_FEATURE_JAVA_TIME=
+ARG BABAHSKA_FEATURE_TRANSIT=
+ARG BABASHKA_FEATURE_XML=
+ARG BABASHKA_FEATURE_YAML=
+ARG BABASHKA_FEATURE_HTTPKIT_CLIENT=
+ARG BABASHKA_FEATURE_HTTPKIT_SERVER=
+ARG BABASHKA_FEATURE_JDBC=
+ARG BABASHKA_FEATURE_POSTGRESQL=
+ARG BABASHKA_FEATURE_HSQLDB=
+ARG BABASHKA_FEATURE_ORACLEDB=
+ARG BABASHKA_FEATURE_DATASCRIPT=
+ARG BABASHKA_FEATURE_LANTERNA=
+ENV BABASHKA_LEAN=$BABASHKA_LEAN
+ENV BABASHKA_FEATURE_CORE_ASYNC=$BABASHKA_FEATURE_CORE_ASYNC
+ENV BABASHKA_FEATURE_CSV=$BABASHKA_FEATURE_CSV
+ENV BABASHKA_FEATURE_JAVA_NIO=$BABASHKA_FEATURE_JAVA_NIO
+ENV BABASHKA_FEATURE_JAVA_TIME=$BABASHKA_FEATURE_JAVA_TIME
+ENV BABAHSKA_FEATURE_TRANSIT=$BABAHSKA_FEATURE_TRANSIT
+ENV BABASHKA_FEATURE_XML=$BABASHKA_FEATURE_XML
+ENV BABASHKA_FEATURE_YAML=$BABASHKA_FEATURE_YAML
+ENV BABASHKA_FEATURE_HTTPKIT_CLIENT=$BABASHKA_FEATURE_HTTPKIT_CLIENT
+ENV BABASHKA_FEATURE_HTTPKIT_SERVER=$BABASHKA_FEATURE_HTTPKIT_SERVER
+ENV BABASHKA_FEATURE_JDBC=$BABASHKA_FEATURE_JDBC
+ENV BABASHKA_FEATURE_POSTGRESQL=$BABASHKA_FEATURE_POSTGRESQL
+ENV BABASHKA_FEATURE_HSQLDB=$BABASHKA_FEATURE_HSQLDB
+ENV BABASHKA_FEATURE_ORACLEDB=$BABASHKA_FEATURE_ORACLEDB
+ENV BABASHKA_FEATURE_DATASCRIPT=$BABASHKA_FEATURE_DATASCRIPT
+ENV BABASHKA_FEATURE_LANTERNA=$BABASHKA_FEATURE_LANTERNA
+
 COPY . .
 RUN ./script/uberjar
 RUN ./script/compile

doc/build.md

@@ -60,6 +60,24 @@ $ export BABASHKA_XMX="-J-Xmx6500m"
 Note: setting the max heap size to a low value can cause the build to crash or
 take long to complete.
 
+### Alternative: Build inside Docker
+
+To build a Linux version of babashka, you can use `docker build`, enabling the 
+desired features via `--build-arg` like this:
+
+```shell
+docker build --build-arg BABASHKA_FEATURE_JDBC=true --target BASE -t bb-builder .
+container_id=$(docker create bb-builder)
+docker cp $container_id:/opt/bb bb # copy to ./bb on the host file system
+docker rm $container_id
+``` 
+
+NOTE: If you get _Error: Image build request failed with exit status 137_ then
+check whether Docker is allowed to use enough memory (e.g. in Docker Desktop
+preferences). If it is, then increase the memory GraalVM can use, for example
+by adding `--build-arg BABASHKA_XMX="-J-Xmx8g"` 
+(or whatever Docker has available, bigger than the default).
+
 ## Windows
 
 Run `script\uberjar.bat` followed by `script\compile.bat`.