bake: replace --list-targets and --list-variables flags with --list flag

[crazy-max]

follow-up #2556 (review)

• Replace --list-targets and --list-variables flags with --list flag and put it out of experimental.
• --print and --list are now mutually exclusive.
• Add json format support for --list flag.

$ docker buildx bake --list=targets
#1 [internal] load local bake definitions
#1 reading docker-bake.hcl 4.97kB / 4.97kB done
#1 DONE 0.0s
TARGET                          DESCRIPTION
binaries
binaries-cross
default                         binaries
govulncheck
image
image-cross
image-local
integration-test
integration-test-base
lint
lint-gopls
meta-helper
mod-outdated
release
test
update-authors
update-docs
update-generated-files
update-vendor
validate                        lint, lint-gopls, validate-docs, validate-golangci, validate-vendor
validate-authors
validate-docs
validate-generated-files
validate-golangci               Validate .golangci.yml schema (does not run Go linter)
validate-vendor

$ docker buildx bake --list=variables
#1 [internal] load local bake definitions
#1 reading docker-bake.hcl 4.97kB / 4.97kB done
#1 DONE 0.0s
VARIABLE                        VALUE   DESCRIPTION
DESTDIR                         ./bin
DOCS_FORMATS                    md
GOLANGCI_LINT_MULTIPLATFORM
GOVULNCHECK_FORMAT              <null>
GO_VERSION                      <null>
HTTPS_PROXY
HTTP_PROXY
NO_PROXY
TEST_BUILDKIT_TAG               <null>
TEST_COVERAGE                   <null>

$ docker buildx bake --list=type=targets,format=json
#1 [internal] load local bake definitions
#1 reading docker-bake.hcl 4.97kB / 4.97kB done
#1 DONE 0.0s
[
  {
    "name": "binaries"
  },
  {
    "name": "binaries-cross"
  },
  {
    "name": "default",
    "description": "binaries",
    "group": true
  },
  {
    "name": "govulncheck"
  },
  {
    "name": "image"
  },
  {
    "name": "image-cross"
  },
  {
    "name": "image-local"
  },
  {
    "name": "integration-test"
  },
  {
    "name": "integration-test-base"
  },
  {
    "name": "lint"
  },
  {
    "name": "lint-gopls"
  },
  {
    "name": "meta-helper"
  },
  {
    "name": "mod-outdated"
  },
  {
    "name": "release"
  },
  {
    "name": "test"
  },
  {
    "name": "update-authors"
  },
  {
    "name": "update-docs"
  },
  {
    "name": "update-generated-files"
  },
  {
    "name": "update-vendor"
  },
  {
    "name": "validate",
    "description": "lint, lint-gopls, validate-docs, validate-golangci, validate-vendor",
    "group": true
  },
  {
    "name": "validate-authors"
  },
  {
    "name": "validate-docs"
  },
  {
    "name": "validate-generated-files"
  },
  {
    "name": "validate-golangci",
    "description": "Validate .golangci.yml schema (does not run Go linter)"
  },
  {
    "name": "validate-vendor"
  }
]

$ docker buildx bake --list=type=variables,format=json
#1 [internal] load local bake definitions
#1 reading docker-bake.hcl 4.97kB / 4.97kB done
#1 DONE 0.0s
[
  {
    "name": "DESTDIR",
    "value": "./bin"
  },
  {
    "name": "DOCS_FORMATS",
    "value": "md"
  },
  {
    "name": "GOLANGCI_LINT_MULTIPLATFORM",
    "value": ""
  },
  {
    "name": "GOVULNCHECK_FORMAT"
  },
  {
    "name": "GO_VERSION"
  },
  {
    "name": "HTTPS_PROXY",
    "value": ""
  },
  {
    "name": "HTTP_PROXY",
    "value": ""
  },
  {
    "name": "NO_PROXY",
    "value": ""
  },
  {
    "name": "TEST_BUILDKIT_TAG"
  },
  {
    "name": "TEST_COVERAGE"
  }
]

[crazy-max]

Was wondering if instead it would have been better to use groups and targets field:

$ docker buildx bake --list=type=targets,format=json
#1 [internal] load local bake definitions
#1 reading docker-bake.hcl 4.97kB / 4.97kB done
#1 DONE 0.0s
{
  "groups": [
    {
      "name": "default",
      "targets": ["binaries"]
    },
    {
      "name": "validate",
      "targets": ["lint", "lint-gopls", "validate-docs", "validate-golangci", "validate-vendor"]
    }
  ],
  "targets": [
    {
      "name": "binaries"
    },
    {
      "name": "binaries-cross"
    },
    {
      "name": "govulncheck"
    },
    {
      "name": "image"
    },
    {
      "name": "image-cross"
    },
    {
      "name": "image-local"
    },
    {
      "name": "integration-test"
    },
    {
      "name": "integration-test-base"
    },
    {
      "name": "lint"
    },
    {
      "name": "lint-gopls"
    },
    {
      "name": "meta-helper"
    },
    {
      "name": "mod-outdated"
    },
    {
      "name": "release"
    },
    {
      "name": "test"
    },
    {
      "name": "update-authors"
    },
    {
      "name": "update-docs"
    },
    {
      "name": "update-generated-files"
    },
    {
      "name": "update-vendor"
    },
    {
      "name": "validate-authors"
    },
    {
      "name": "validate-docs"
    },
    {
      "name": "validate-generated-files"
    },
    {
      "name": "validate-golangci",
      "description": "Validate .golangci.yml schema (does not run Go linter)"
    },
    {
      "name": "validate-vendor"
    }
  ]
}

It's a bit inconsistent with table format but more readable imo.

WDYT?

[tonistiigi]

I'm not sure about completely separating this, but in JSON view I think separate fields for description and subtargets would make sense.