Fixes two panics

Fixes two edge cases where panics can occur.
- If there is no package information in the descriptor at all, panics trying to generate repos list
- If there is only a single package set, panics when trying to pick the first repo

Signed-off-by: Daniel Mikusa <dmikusa@vmware.com>

README.md

@@ -140,9 +140,11 @@ package:
 
 `package` is an object that describes the `repositories` a buildpackage should be published to as well as whether to include the buildpackage's dependencies when creating it (`false` by default).  If defined, a `create-package` workflow is created that creates and publishes a new package when a release is published as well as adds a `create-package` job to the tests workflow that is run on each PR and each commit.  It will also add additional content to the draft release notes about the contents of the build package and will update the digest of the buildpackage in the published release notes.  If `register` is `true`, after the package is created, it is registered with the [Buildpack Registry Index](https://github.com/buildpacks/registry-index).
 
-`repository` is deprecated in favour of a list of repositories, as described below. This should be left empty if the `repositories` property is used. If a value is specified, this will take preference over `repositories`
+`repository` is the primary repository. It is the repository registered with the Buildpack Registry Index. It defaults to the first entry in `repositories` so if a value is specified, this will take preference over `repositories[0]`.
 
-`repositories` is the list of repositories that the image should be published to. The list is an array of strings, and the Docker Hub address should be be listed as the first item, as per the above example - this address will be added to the Buildpack Registry Index. The image will be copied to subsequent repository addresses specified. 
+`repositories` is the list of repositories that the image should be published to. The list is an array of strings. If `repository` is not set then the first registry address will be used for `repository`, which is the address that's added to the Buildpack Registry Index. When multiple repositories are set, the image will be packaged once and then copied to subsequent repository addresses specified for efficiency.
+
+If you have a single repository to which you want to publish, using `repository` is preferred but it is the same as setting `repositories` to a single repository. If you have multiple repositories, you may set both `repository` and `repositories` but that's only necessary if you need a repository registered with the Buildpack Registry Index that's not the first in the `repositories` list.
 
 `source_path` is the optional path to the buildpack's directory relative to the repository's root. Defaults to the repository root.
 
@@ -475,6 +477,19 @@ with:
   token: ${{ secrets.GITHUB_TOKEN }}
 ```
 
+### Liberty Dependency
+The Liberty Dependency watches a [Maven Repository](https://repo1.maven.org/maven2) for new versions.
+
+```yaml
+uses: docker://ghcr.io/paketo-buildpacks/actions/liberty-dependency:main
+with:
+  uri:         https://repo1.maven.org/maven2
+  group_id:    org.apache.maven
+  artifact_id: apache-maven
+  classifier:  bin
+  packaging:   tar.gz
+```
+
 ### Maven Dependency
 The Maven Dependency queries a [Maven Repository](https://repo1.maven.org/maven2) for new versions.
 

octo/create_package.go

@@ -31,21 +31,22 @@ import (
 )
 
 func ContributeCreatePackage(descriptor Descriptor) (*Contribution, error) {
-	if descriptor.Package == nil {
+	if !descriptor.Package.Enabled {
 		return nil, nil
 	}
 
-	var repos string
-	if descriptor.Package.Repository != "" {
-		repos = descriptor.Package.Repository
-	} else {
-		repos = strings.Join(descriptor.Package.Repositories, " ")
+	if descriptor.Package.Repository == "" && len(descriptor.Package.Repositories) > 0 {
+		descriptor.Package.Repository = descriptor.Package.Repositories[0]
+	}
+
+	if len(descriptor.Package.Repositories) == 0 && descriptor.Package.Repository != "" {
+		descriptor.Package.Repositories = append(descriptor.Package.Repositories, descriptor.Package.Repository)
 	}
 
 	file := filepath.Join(descriptor.Path, "buildpack.toml")
 	s, err := ioutil.ReadFile(file)
 	if err != nil {
-		return nil, fmt.Errorf("unable to read %s\n%w", file, err)
+		return nil, fmt.Errorf("unable to read foo %s\n%w", file, err)
 	}
 
 	var b libcnb.Buildpack
@@ -125,7 +126,7 @@ func ContributeCreatePackage(descriptor Descriptor) (*Contribution, error) {
 						Name: "Package Buildpack",
 						Run:  StatikString("/package-buildpack.sh"),
 						Env: map[string]string{
-							"PACKAGES":      repos,
+							"PACKAGES":      strings.Join(descriptor.Package.Repositories, " "),
 							"PUBLISH":       "true",
 							"VERSION":       "${{ steps.version.outputs.version }}",
 							"VERSION_MAJOR": "${{ steps.version.outputs.version-major }}",
@@ -147,7 +148,7 @@ func ContributeCreatePackage(descriptor Descriptor) (*Contribution, error) {
 							"token":   descriptor.Package.RegistryToken,
 							"id":      b.Info.ID,
 							"version": "${{ steps.version.outputs.version }}",
-							"address": fmt.Sprintf("%s@${{ steps.package.outputs.digest }}", descriptor.Package.Repositories[0]),
+							"address": fmt.Sprintf("%s@${{ steps.package.outputs.digest }}", descriptor.Package.Repository),
 						},
 					},
 				},

octo/descriptor.go

@@ -106,6 +106,7 @@ type Package struct {
 	RegistryToken       string `yaml:"registry_token"`
 	Platform            Platform
 	SourcePath          string `yaml:"source_path"`
+	Enabled             bool
 }
 
 const (
@@ -159,7 +160,13 @@ func NewDescriptor(path string) (Descriptor, error) {
 		}
 	}
 
-	if d.Package != nil && d.Package.Platform.OS == "" {
+	if d.Package == nil {
+		d.Package = &Package{}
+	} else {
+		d.Package.Enabled = true
+	}
+
+	if d.Package.Platform.OS == "" {
 		d.Package.Platform.OS = PlatformLinux
 	}
 

octo/test.go

@@ -36,11 +36,12 @@ func ContributeTest(descriptor Descriptor) (*Contribution, error) {
 		return nil, nil
 	}
 
-	var repos []string
-	if descriptor.Package.Repository != "" {
-		repos = append(repos, descriptor.Package.Repository)
-	} else {
-		repos = descriptor.Package.Repositories
+	if descriptor.Package.Repository == "" && len(descriptor.Package.Repositories) > 0 {
+		descriptor.Package.Repository = descriptor.Package.Repositories[0]
+	}
+
+	if len(descriptor.Package.Repositories) == 0 && descriptor.Package.Repository != "" {
+		descriptor.Package.Repositories = append(descriptor.Package.Repositories, descriptor.Package.Repository)
 	}
 
 	w := actions.Workflow{
@@ -189,7 +190,7 @@ func ContributeTest(descriptor Descriptor) (*Contribution, error) {
 		w.Jobs["create-builder"] = j
 	}
 
-	if descriptor.Package != nil {
+	if descriptor.Package.Enabled {
 		format := FormatImage
 		if descriptor.Package.Platform.OS == PlatformWindows {
 			format = FormatFile
@@ -250,14 +251,14 @@ func ContributeTest(descriptor Descriptor) (*Contribution, error) {
 					Run:  StatikString("/package-buildpack.sh"),
 					Env: map[string]string{
 						"FORMAT":   format,
-						"PACKAGES": "test1 test2",
+						"PACKAGES": "test",
 						"VERSION":  "${{ steps.version.outputs.version }}",
 					},
 				},
 			},
 		}
 
-		for _, repo := range repos {
+		for _, repo := range descriptor.Package.Repositories {
 			if !strings.Contains(repo, "paketo-buildpacks") {
 				j.Steps = append(NewDockerCredentialActions(descriptor.DockerCredentials), j.Steps...)
 			}