Buildpack incompatible with building in /app ("cp: cannot stat '/app/!(tmp)': No such file or directory")

[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.

Once this change comes into effect this buildpack will error like so:

remote: -----> Python app detected
remote: cp: cannot stat '/app/!(tmp)': No such file or directory

This is because the buildpack tries to move the contents of /app to a temporary location, followed by moving BUILD_DIR (which is now /app) into /app.

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, the file moves (at both the start and end of the build) need to be put behind a conditional that first checks if BUILD_DIR is already /app:

heroku-buildpack-python-sklearn/bin/compile

Lines 42 to 55 in bd93808

	# Directory Hacks for path consistiency.
	APP_DIR='/app'
	TMP_APP_DIR=$CACHE_DIR/tmp_app_dir
	# Copy Anvil app dir to temporary storage...
	mkdir -p $TMP_APP_DIR
	deep-mv $APP_DIR $TMP_APP_DIR
	# Copy Application code in.
	deep-mv $BUILD_DIR $APP_DIR
	# Set new context.
	ORIG_BUILD_DIR=$BUILD_DIR
	BUILD_DIR=$APP_DIR

heroku-buildpack-python-sklearn/bin/compile

Lines 202 to 203 in bd93808

	deep-mv $BUILD_DIR $ORIG_BUILD_DIR
	deep-mv $TMP_APP_DIR $APP_DIR

[dbrgn]

Hi @edmorley. Thanks for the information! I haven't touched this repository in years, it's not maintained anymore. README links to a fork that used to be active, not sure if it still is.

I'll archive the repo to avoid future confusion.

Cheers!