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 fail with errors like:

mv: cannot copy a directory, '/app', into itself, '/app/thunder'

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 lines will be needed:

heroku-buildpack-thunder/bin/compile

Lines 36 to 37 in 1493f71

	mv $build_dir /app/thunder
	mkdir $build_dir

heroku-buildpack-thunder/bin/compile

Lines 43 to 44 in 1493f71

	cd ${build_dir}
	mv /app/thunder ${build_dir}

Many thanks :-)