Limitations for detect API

[sambhav]

The current detect API seems like it cannot handle use cases like so -

Let's say we have 3 buildpacks -

1. System package manager (like apt or yum but it can run without root - for eg conda)
2. A go buildpack that provides go binaries
3. A go mod buildpack that knows how to build applications with go.mod.

Now let's say the provisions and requirements of each buildpack look like so

System package manager -

This is responsible for installing any system-wide packages

Provides - {"name": "system-packages"}

Go buildpack

This is responsible for requesting the appropriate go system package and setting the go env. vars like GOPROXY or GOPRIVATE or GOPATH etc.

Provides - {"name": "go"}

Note - the go buildpack can also request other go versions here if it knows which versions to request before hand. It supports versions 1.14, 1.15 and 1.16 let's say.

Requires - {"name": "system-packages", "metadata": {"packages": "go-1.16"}}

Go mod buildpack

This looks at the go.mod file and reads the required version tag off it. For eg the version constraint it might read might be something like >=1.16

Provides - {"name": "go-mod"}
Requires - {"name": "go", "metadata": {"version": ">=1.16"}}

There isn't anyway for this current set of buildpacks to pass the correct information to one another.