It looks like this line contain a wrong syntax. I'm not fully sure though: https://github.com/CHH/heroku-buildpack-php/commit/63f174c5f7839f5ccca5d75a41945d70362460ae#diff-c7b43338c09c3c9afd420fd8b6bb5198R373 As a result process crash is not properly handled and the docker keep on running.
It looks like this line contain a wrong syntax. I'm not fully sure though:
63f174c#diff-c7b43338c09c3c9afd420fd8b6bb5198R373
As a result process crash is not properly handled and the docker keep on running.