Add support for testing binaries in staging/ on S3

This will allow for faster and more transparent deploys for Python and
other built dependencies.

.gitignore

@@ -8,4 +8,5 @@ repos/*
 #Venv
 buildpack/*
 
-builds/dockerenv
+builds/dockerenv.staging*
+builds/dockerenv.production

Makefile

@@ -8,6 +8,14 @@ check:
 	@shellcheck -x bin/steps/collectstatic bin/steps/eggpath-fix  bin/steps/eggpath-fix2 bin/steps/gdal bin/steps/geo-libs bin/steps/mercurial bin/steps/nltk bin/steps/pip-install bin/steps/pip-uninstall bin/steps/pipenv bin/steps/pipenv-python-version bin/steps/pylibmc bin/steps/python
 	@shellcheck -x bin/steps/hooks/*
 
+test-staging:
+	@echo "Running tests against staged binaries..."
+	@docker run -v $(shell pwd):/buildpack:ro --rm -it -e "STACK=heroku-16" -e "TEST_STAGED_S3_BINARIES=1" heroku/heroku:16-build bash -c 'cp -r /buildpack /buildpack_test; cd /buildpack_test/; test/run;'
+	@echo ""
+	@echo "Running tests in docker (heroku-18)..."
+	@docker run -v $(shell pwd):/buildpack:ro --rm -it -e "STACK=heroku-18" -e "TEST_STAGED_S3_BINARIES=1" heroku/heroku:18-build bash -c 'cp -r /buildpack /buildpack_test; cd /buildpack_test/; test/run;'
+	@echo ""
+
 test-heroku-16:
 	@echo "Running tests in docker (heroku-16)..."
 	@docker run -v $(shell pwd):/buildpack:ro --rm -it -e "STACK=heroku-16" heroku/heroku:16-build bash -c 'cp -r /buildpack /buildpack_test; cd /buildpack_test/; test/run;'

bin/compile

@@ -43,6 +43,13 @@ VENDOR_URL="https://lang-python.s3.amazonaws.com/$STACK"
 if [[ -n ${BUILDPACK_VENDOR_URL:-} ]]; then
     VENDOR_URL="$BUILDPACK_VENDOR_URL"
 fi
+
+# Build binaries (python runtimes, etc) in the /staging/ directory on S3. Test
+these binaries for compatibility when passed this environment variable.
+if [ "$TEST_STAGED_S3_BINARIES" == "1" ]; then
+    echo "Testing staged binaries..."
+    VENDOR_URL="https://lang-python.s3.amazonaws.com/staging/$STACK"
+fi
 export VENDOR_URL
 
 # Default Python Versions