Buildpack incompatible with building in /app

[edmorley]

Hi

I'm on the team that maintains Heroku's build system and official buildpacks, and wanted to let you know about a future incompatibility with this buildpack.

The directory in which the Heroku build system performs builds is currently a path like/tmp/build_<hash>.

In the near future this path will be changing to /app so that the build-time and run-time app locations are the same path - in order to resolve a number of long standing bugs, and reduce the number of hacks buildpacks have to use to work around non-relocatable languages/toolchains.

This change will mean builds using this buildpack will show warnings like:

remote: -----> Python + OpenCV + Numpy + Scipy app detected
remote: cp: '/app/requirements.txt' and '/app/requirements.txt' are the same file
remote: cp: '/app/test' and '/app/test' are the same file
remote: -----> Generating environment
remote:        Fetching...
remote:        Unpacking...
...
remote: -----> Creating environment variables.
remote: cp: '/app/.heroku' and '/app/.heroku' are the same file
remote: cp: '/app/.profile.d' and '/app/.profile.d' are the same file
remote: -----> Buildpack installed.

...and worse, the build will appear to succeed (exit non-zero) due to this buildpack not using Bash "exit on error", however the contents of the app source will not be copied correctly into the build, meaning the app will fail to boot.

To reproduce, the new behaviour can be enabled manually (ahead of it being the new default), using:

heroku labs:enable build-in-app-dir -a my_app_name

To fix, some reworking of these parts will be needed (eg skipping the move if BUILD_DIR is already /app):

heroku-buildpack-python-opencv-scipy/bin/compile

Lines 21 to 60 in c9605c2

	# Does some serious copying.
	deep-cp() {
	declare source="$1" target="$2"
	mkdir -p "$target"
	# cp doesn't like being called without source params,
	# so make sure they expand to something first.
	# subshell to avoid surprising caller with shopts.
	(
	shopt -s nullglob dotglob
	set -- "$source"/!(tmp|.|..)
	[[ $# == 0 ]] || cp -a "$@" "$target"
	)
	}
	# Does some serious moving.
	deep-mv() {
	deep-cp "$1" "$2"
	deep-rm "$1"
	}
	# Does some serious deleting.
	deep-rm() {
	# subshell to avoid surprising caller with shopts.
	(
	shopt -s dotglob
	rm -rf "$1"/!(tmp|.|..)
	)
	}
	###################################
	BUILD_DIR=$1
	CACHE_DIR=$2
	APP_DIR="/app"
	deep-mv $BUILD_DIR $APP_DIR
	ORIG_BUILD_DIR=$BUILD_DIR
	BUILD_DIR=$APP_DIR
	cd $BUILD_DIR

heroku-buildpack-python-opencv-scipy/bin/compile

Line 99 in c9605c2

deep-mv $BUILD_DIR $ORIG_BUILD_DIR