Optional buildpack value lost, or spec is unclear. about lifecycle HOT 4 CLOSED

The BuildpackMap is constructed from the buildpack.toml files in each buildpack on the filesystem[1]. It has no concept of Optional (even though it re-uses the Buildpack struct with that field).

Each buildpack in BuildpackMap can be referenced multiple times in order.toml or group.toml. When lookup is called in ReadOrder, we copy the optional field value onto the value from the BuildpackMap before returning it, so that you can convert an order.toml file that is missing the info from the buildpack.toml files to a fully-hydrated structure in memory. In the case of group.toml/ReadGroup, the copying of the Optional field is meaningless, because optionality isn't relevant after the detection process (which removes optional buildpacks that failed detection).

This code could be tidied up a bit (perhaps by creating different types of buildpack structs for different use cases), but I think the behavior (and spec[2]) are both accurate. Are you seeing otherwise in the behavior of the lifecycle?

[1] https://github.com/buildpack/lifecycle/blob/master/map.go#L21
[2] https://github.com/buildpack/spec/blob/master/platform.md#data-format

from lifecycle.

@squee1945 @sclevine

Sounds like this is a critique of the code readability rather than a bug. I'm inclined to close unless anyone feels strongly to the contrary (we can certainly refactor for clarity but this issue feels misleading)

from lifecycle.

from lifecycle.

@squee1945 I am closing this issue. Feel free to open an issue or PR on the spec repo if you feel that the specification lacks clarity.

from lifecycle.