Heroku Buildpack for Stack

Heroku buildpack for Stack. Based on the excellent heroku-buildpack-ghc

Create an app with this buildpack:

$ heroku create --buildpack https://github.com/mfine/heroku-buildpack-stack.git

Set this buildpack on an existing app:

$ heroku buildpacks:set https://github.com/mfine/heroku-buildpack-stack

Binary executables are placed in /app/.local/bin/ after compilation, a directory which Heroku includes in your $PATH, so assuming that your application is binding to $PORT, you can serve your app by creating a Procfile at your project root that defines a web process type for the executable defined in your .cabal file:

$ cat *.cabal | grep executable
executable YOURAPPNAME-exe

$ echo "web: YOURAPPNAME-exe" >> Procfile

To avoid committing secrets into stack.yaml for access to private repos, an app's config vars values can be substituted for tags enclosed in double brackets. For example, given a stack.yaml containing:

packages:
-location:
    git: https://mfine:{{GITPASS}}@github.com/mfine/heroku-buildpack-stack.git

and an application with config vars:

$ heroku config -app calm-storm-51595
=== murmuring-beyond-51595 Config Vars
GITPASS: abc123
$

before compilation, the stack.yaml will be substituted as follows:

packages:
-location:
    git: https://mfine:abc123@github.com/mfine/heroku-buildpack-stack.git

This buildpack now supports an optional Makefile, in case you need to coordinate other build steps with Stack. It assumes that the Makefile includes a make install target that uses the Stack build command with the flag --copy-bins. For example, a possible install target configuration in the Makefile could be:

install:
    stack build --copy-bins