Feature summary
Add the Multi Procfile buildpack ()https://elements.heroku.com/buildpacks/heroku/heroku-buildpack-multi-procfile)
Use case(s)
Using the Build Service with a monorepo containing multiple tools does not work as only one top-level procfile is supported by the current build packs.
Benefits
Building tools contained in monorepos is supported.
That buildpack has been >4 years without any commits, and it does not seem widely used either, I would prefer not having to support it if it does not solve a blocking issue or helps many users.
Looking at the code in the other task, https://gitlab.wikimedia.org/countcount/xlinks/, it seems that only one of the apps is a webservice, so that would work well, as the only restriction we have for a Procfile is that we only support one webservice per Procfile (same as one webservice per tool).
Is that correct? can you try adding up the entries into one Procfile?
We are working on a more flexible hosting that will allow for multiple webservice components per tool, though that might take some time to get implemented (hopefully <1 year, but can't promise anything).
Back then it wasn't possible due to the peculiarities of the Rust buildpack, but now that I have restructured it to be a Rust "workspace" I will give it another shot.