pack inspect-builder should show digest of underlying build image

[zmackie]

It would be nice to trace the composing images of a builder

pack inspect-builder cloudfoundry/cnb:0.0.39-bionic
Inspecting builder: cloudfoundry/cnb:0.0.39-bionic

REMOTE:

Description: Ubuntu bionic base image with buildpacks for Java, NodeJS and Golang

Created By:
  Name: Pack CLI
  Version: v0.5.0 (git sha: c9cfac75b49609524e1ea33f809c12071406547c)

Stack: io.buildpacks.stacks.bionic

Lifecycle:
  Version: 0.5.0
  Buildpack API: 0.2
  Platform API: 0.1

Run Images:
  cloudfoundry/run:base-cnb 

Build Images:
  cloudfoundry/build:base (sha256:44bfc2c352109a56f968a397b4d2d2a453a58af045a1141bf01206c8c7c16a26

...[TRIMMED]

[jromero]

Recording the sha for the build image at the creation of builder makes sense.

For run images, the intent is that run images are updated after a builder is created. Additionally the run-mirrors feature can route to a different run image. Both of this aspects present problems that even if we were to capture the sha of the run image at builder creation time it could be perceived as misinformation given that the run image can be changed at any point thereafter.

We could print out what run image sha we would use but that doesn't seem to fit into what you might be after. Does it?

[zmackie]

@jromero I guess reporting anything that's pinned down (eg. the build image) would be helpful. Essentially any piece of metadata about the component parts of the builder would be useful

[natalieparellano]

Updated @zmackie's comment above to only specify the sha for build images.