Improve docker layer caching and build times

Currently, the apt-get package install layer is invalidated anytime we
update npm dependencies. This commit splits package installation and npm
dependency installation into separate steps, which should improve docker
layer caching and speed up build times.

This commit also extracts the inline docs installation into a separate
bin script.

Dockerfile

@@ -1,32 +1,26 @@
 FROM node:6.10.0-slim
-MAINTAINER Code Climate <[email protected]>
+LABEL maintainer "Code Climate <[email protected]>"
 
 RUN apt-key adv --fetch-keys http://dl.yarnpkg.com/debian/pubkey.gpg && \
     echo "deb http://dl.yarnpkg.com/debian/ stable main" | tee /etc/apt/sources.list.d/yarn.list && \
-    apt-get update && \
-    apt-get install -y yarn
+    apt-get update
 
 WORKDIR /usr/src/app
-COPY package.json yarn.lock /usr/src/app/
-
-RUN yarn install
-
-RUN apt-get update && \
-    apt-get install -y git jq && \
-    git clone https://github.com/eslint/eslint.git && \
-    ESLINT_DOCS_VERSION=`npm -j ls eslint | jq -r .dependencies.eslint.version` && \
-    cd eslint && \
-    git checkout v$ESLINT_DOCS_VERSION && \
-    cd .. && \
-    mkdir -p /usr/src/app/lib/docs/rules/ && \
-    cp ./eslint/docs/rules/* /usr/src/app/lib/docs/rules/ && \
-    rm -rf eslint && \
-    apt-get purge -y git jq && \
-    apt-get autoremove -y
-
-RUN adduser -u 9000 --gecos "" --disabled-password app
-COPY . /usr/src/app
-RUN chown -R app:app /usr/src/app
+COPY bin/docs ./bin/docs
+COPY engine.json package.json yarn.lock ./
+
+RUN apt-get install -y git jq yarn && \
+    yarn install && \
+    version="v$(npm -j ls eslint | jq -r .dependencies.eslint.version)" && \
+    bin/docs "$version" && \
+    cat engine.json | jq ".version = \"$version\"" > /tmp/engine.json && \
+    apt-get purge -y git jq yarn && \
+    apt-get autoremove --yes
+
+RUN adduser --uid 9000 --gecos "" --disabled-password app
+COPY . ./
+RUN chown -R app:app ./ && \
+    mv /tmp/engine.json ./
 
 USER app
 

bin/docs

@@ -0,0 +1,12 @@
+#!/bin/bash
+
+set -e
+
+version=$1
+printf "Pulling docs from ESlint %s\n" "$version"
+
+git clone https://github.com/eslint/eslint.git /tmp/eslint
+(cd /tmp/eslint && git reset --hard "$version")
+mkdir --parents ./lib/docs
+cp --recursive /tmp/eslint/docs/rules ./lib/docs/rules
+rm --force --recursive /tmp/eslint