Deploy with auto build (#156)

* Use Node buildpack‘s auto build

* Remove NODE_ENV=development workaround since Node buildpack installs devDeps for build & auto-runs build.

* 📚 link to Dev Center for Node.js build customization

* Switch to new Node auto build behavior ahead of release

* Upgrade to "Node auto build" release version of inner buildpack

.buildpacks

@@ -1,3 +1,3 @@
 https://github.com/heroku/heroku-buildpack-nodejs.git
-https://github.com/mars/create-react-app-inner-buildpack.git#v8.0.0
+https://github.com/mars/create-react-app-inner-buildpack.git#v9.0.0
 https://github.com/heroku/heroku-buildpack-static.git

README.md

@@ -358,7 +358,9 @@ ex: `REACT_APP_FILEPICKER_API_KEY` ([Add-on config vars](#user-content-add-on-co
 
 ### Compile-time configuration
 
-Supports [`REACT_APP_`](https://github.com/facebook/create-react-app/blob/master/packages/react-scripts/template/README.md#adding-custom-environment-variables), `NODE_`, `NPM_`, & `HEROKU_` prefixed variables.
+Supports all config vars, including [`REACT_APP_`](https://github.com/facebook/create-react-app/blob/master/packages/react-scripts/template/README.md#adding-custom-environment-variables), `NODE_`, `NPM_`, & `HEROKU_` prefixed variables.
+
+☝️🤐 ***Use secrets carefully.** If these values are embedded in the JavaScript bundle, like with `REACT_APP_` vars, then they may be accessed by anyone who can see the React app.*
 
 Use Node's [`process.env` object](https://nodejs.org/dist/latest-v10.x/docs/api/process.html#process_process_env).
 
@@ -528,15 +530,12 @@ This buildpack combines several buildpacks, specified in [`.buildpacks`](.buildp
    * installs `node`, puts on the `$PATH`
    * version specified in [`package.json`, `engines.node`](https://devcenter.heroku.com/articles/nodejs-support#specifying-a-node-js-version)
    * `node_modules/` cached between deployments
-   * `NODE_ENV` at buildtime:
-     * defaults to `NODE_ENV=development` to install the build tooling of create-react-app's dev dependencies, like `react-scripts`
-     * honors specific setting of `NODE_ENV`, like `NODE_ENV=test` for [automated testing](#user-content-testing) in [`bin/test`](bin/test-compile)
-     * but forces `NODE_ENV=production` to be `development` to ensure dev dependencies are available for build
-2. [`mars/create-react-app-inner-buildpack`](https://github.com/mars/create-react-app-inner-buildpack)
    * production build for create-react-app
-     * executes the npm package's build script; create-react-app default is `react-scripts build`
-     * exposes `REACT_APP_`, `NODE_`, `NPM_`, & `HEROKU_` prefixed env vars to the build script
+     * [executes the npm package's build script](https://devcenter.heroku.com/changelog-items/1557); create-react-app default is `react-scripts build`
+     * exposes all env vars to the build script
      * generates a production bundle regardless of `NODE_ENV` setting
+     * customize further with [Node.js build configuration](https://devcenter.heroku.com/articles/nodejs-support#customizing-the-build-process)
+2. [`mars/create-react-app-inner-buildpack`](https://github.com/mars/create-react-app-inner-buildpack)
    * sets default [web server config](#user-content-web-server) unless `static.json` already exists
    * enables [runtime environment variables](#user-content-environment-variables)
 3. [`heroku/static` buildpack](https://github.com/heroku/heroku-buildpack-static)

bin/compile

@@ -23,6 +23,9 @@ CACHE_DIR=$2
 ENV_DIR=$3
 BP_DIR=`cd $(dirname $0); cd ..; pwd`
 
+# Switch to new Node auto build behavior ahead of release
+export NEW_BUILD_SCRIPT_BEHAVIOR=true
+
 # Use architecture of multi-buildpack to compose behavior.
 # https://github.com/heroku/heroku-buildpack-multi
 cp $BP_DIR/.buildpacks $BUILD_DIR/.buildpacks
@@ -31,21 +34,6 @@ branch=""
 dir=$(mktemp -t buildpackXXXXX)
 rm -rf $dir
 
-echo "-----> Configure create-react-app build environment"
-# Set env vars for the inner buildpacks in `.buildpacks`
-# * during compile, install build tooling (devDependencies) with npm & Yarn
-# * in runtime, NODE_ENV is not used (this buildpack launches a static web server)
-export NPM_CONFIG_PRODUCTION=false
-INHERITED_NODE_ENV="${NODE_ENV:-development}"
-if [ "$INHERITED_NODE_ENV" = "production" ]
-  then
-  echo '       Setting `NODE_ENV=development` to install dependencies for `npm build`'
-  export NODE_ENV=development
-else
-  echo "       Using \`NODE_ENV=${INHERITED_NODE_ENV}\`"
-  export NODE_ENV="${INHERITED_NODE_ENV}"
-fi
-
 echo "=====> Downloading Buildpack: $url"
 
 if [[ "$url" =~ \.tgz$ ]] || [[ "$url" =~ \.tgz\? ]]; then