Implementation of target env vars is misleading

[natalieparellano]

Summary

To provide CNB_TARGET_* vars in the buildpack env, the builder concatenates these to the lifecycle's env. This works because the CNB_TARGET_* vars are added to the "allow list" of env vars that the lifecycle will pass through to buildpacks.

However, this is misleading. Someone reading the code might think that CNB_TARGET_* vars need to be set in the lifecycle's env, but this is not the case (the analyzer reads this data from the run image).

We should use something like WithOverrides to append target vars to the buildpack env in builder.go.

Note this functionality is covered by acceptance so it should be safe to refactor at the unit level.

Context

lifecycle version

0.17.0+

platform version(s)

0.12+

[UtkarshUmre]

I'm new to this project, but I'm interested in working on this good first issue. May I give it a try?

[natalieparellano]

@UtkarshUmre we would love to have your help with this! Please let us know if there is any additional guidance we can provide that would be helpful

[sarthaksarthak9]

@UtkarshUmre r u still working on this issue?

[UtkarshUmre]

yes @sarthaksarthak9 I'm still working on this issue

[sarthaksarthak9]

yes @sarthaksarthak9 I'm still working on this issue

ok, If u need some help .. I would love to do!!

[UtkarshUmre]

@sarthaksarthak9 thank you for offering your help. I believe I'm going to need assistance with this one. Where can I contact you?

[sarthaksarthak9]

@sarthaksarthak9 thank you for offering your help. I believe I'm going to need assistance with this one. Where can I contact you?

you can ask your query here onwards or can dm me on slack

[natalieparellano]

@UtkarshUmre @sarthaksarthak9 - thank you for offering to help with this one. This was fixed in #1309 while addressing a slightly different albeit related issue. I'm going to close this one

[edmorley]

This is currently in the lifecycle 0.20.0 milestone, however was resolved previously by #1309 which landed in lifecycle 0.19.0 instead. Should the milestone be updated to 0.19.0?