Add pack config default-builder subcommand

[dfreilich]

Signed-off-by: David Freilich dfreilich@vmware.com

Summary

This command allows users to list, set, and unset a value for a default builder in the pack config, with the command having three forms:

• pack config default-builder → lists the current default builder, or prints a clear message if there is none
• pack config default-builder <some-builder> → After validating the builder exists, either locally or in a remote registry, it is added to the pack config, with a success message printed
• pack config default-builder --unset → If there is a default builder configured, it will remove that from the config, and print a success message. If not, it will print a clear message, saying that there wasn't a builder set.

As part of that, I added a deprecation warning to the existing pack set-default-builder command. I also slightly changed the behavior, so that instead of running pack suggest-builder (which has some latency) if no builder is set or the builder set isn't a valid builder, we just recommend that users can run pack suggest-builder.

Additionally, as part of this PR, I configured the rebase command to use dependency injection for the pack config path, given that my testing setup had caused issues with it in the current format.

Output

After

$  out/pack set-default-builder
Warning: Command pack set-default-builder has been deprecated, please use pack config default-builder instead
Usage:
	pack set-default-builder <builder-name> [flags]
Suggested builders:
^C	Google:                gcr.io/buildpacks/builder:v1      Ubuntu 18 base image with buildpacks for .NET, Go, Java, Node.js, and Python
	Heroku:                heroku/buildpacks:18              heroku-18 base image with buildpacks for Ruby, Java, Node.js, Python, Golang, & PHP
	Paketo Buildpacks:     paketobuildpacks/builder:base     Ubuntu bionic base image with buildpacks for Java, NodeJS and Golang
	Paketo Buildpacks:     paketobuildpacks/builder:full     Ubuntu bionic base image with buildpacks for Java, .NET, NodeJS, Golang, PHP, HTTPD and NGINX
	Paketo Buildpacks:     paketobuildpacks/builder:tiny     Tiny base image (bionic build image, distroless run image) with buildpacks for Golang

Tip: Learn more about a specific builder with:
	pack inspect-builder <builder-image>

 $  out/pack config
Interact with Pack's configuration

Usage:
  pack config [command]

Available Commands:
  trusted-builders  Interact with trusted builders
  run-image-mirrors Interact with run image mirrors
  default-builder   List, set and unset the default builder used by other commands

Flags:
  -h, --help   Help for 'config'

Global Flags:
      --no-color     Disable color output
  -q, --quiet        Show less output
      --timestamps   Enable timestamps in output
  -v, --verbose      Show more output

Use "pack config [command] --help" for more information about a command.

$  out/pack config default-builder -h
List, set, and unset the default builder used by other commands.

* To list your default builder, run `pack config default-builder`.
* To set your default builder, run `pack config default-builder <builder-name>`.
* To unset your default builder, run `pack config default-builder --unset`.

For suggested builders, run `pack builder suggest`.

Usage:
  pack config default-builder [flags]

Examples:
pack config default-builder cnbs/sample-builder:bionic

Flags:
  -h, --help    Help for 'config default-builder'
  -u, --unset   Unset the current default builder

Global Flags:
      --no-color     Disable color output
  -q, --quiet        Show less output
      --timestamps   Enable timestamps in output
  -v, --verbose      Show more output

$  out/pack config default-builder
No default builder is set.

For suggested builders, run `pack builder suggest`.

$  out/pack config default-builder some/builder
ERROR: validating that builder some/builder exists: builder some/builder not found

$  out/pack config default-builder paketobuildpacks/builder:tiny
Builder paketobuildpacks/builder:tiny is now the default builder

$  out/pack config default-builder
The current default builder is paketobuildpacks/builder:tiny

$  out/pack config default-builder --unset
Successfully unset default builder

$  out/pack config default-builder
No default builder is set.

For suggested builders, run `pack builder suggest`.

Documentation

• Should this change be documented?
  • Yes, see #___

Related

Resolves #924
Relates to #597

[dfreilich]

Though not strictly necessary for this PR, I changed this to make it easier to test alone, and require fewer mocks created in the trustedBuilder tests.

[dfreilich]

I moved these tests to config_trusted_builder_test.go, which made more semantic sense than testing them here, where we only need to know that the appropriate commands show up.

[dfreilich]

The failure to set args was causing issues with my local tests, so I added it to ensure that it passes, and took the opportunity to do dependency injection. I can revert that if requested, though.

[codecov]

Codecov Report

Merging #982 (e925edf) into main (06704f6) will decrease coverage by 0.14%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main     #982      +/-   ##
==========================================
- Coverage   79.20%   79.07%   -0.13%     
==========================================
  Files         128      126       -2     
  Lines        5581     5540      -41     
==========================================
- Hits         4420     4380      -40     
+ Misses        748      747       -1     
  Partials      413      413              

Flag	Coverage Δ
os_linux	79.07% <100.00%> (-0.04%)	⬇️
os_macos	76.34% <100.00%> (-0.15%)	⬇️
os_windows	100.00% <ø> (ø)
unit	79.07% <100.00%> (-0.13%)	⬇️

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