Adds create-package support for platform

- Pack experimental feature: buildpacks/pack#926

Signed-off-by: Micah Young <[email protected]>

README.md

@@ -119,6 +119,7 @@ package:
   include_dependencies: false
   register:             true
   registry_token:       ${{ secrets.JAVA_REGISTRY_TOKEN }}
+  platform:             { os: "windows" }
 ```
 
 * [Example `create-package.yml`](https://github.com/paketo-buildpacks/adopt-openjdk/blob/main/.github/workflows/create-package.yml)

octo/create-package.sh

@@ -16,3 +16,7 @@ fi
 
 [[ -e package.toml ]] && cp package.toml "${HOME}"/package.toml
 printf '[buildpack]\nuri = "%s"' "${HOME}"/buildpack >> "${HOME}"/package.toml
+
+if [ -n "${PLATFORM_OS}" ]; then
+  printf '[platform]\nos = "%s"' "${PLATFORM_OS}" >> "${HOME}"/package.toml
+fi

octo/create_package.go

@@ -93,6 +93,7 @@ func ContributeCreatePackage(descriptor Descriptor) (*Contribution, error) {
 						Env: map[string]string{
 							"INCLUDE_DEPENDENCIES": strconv.FormatBool(descriptor.Package.IncludeDependencies),
 							"VERSION":              "${{ steps.version.outputs.version }}",
+							"PLATFORM_OS":          descriptor.Package.Platform.OS,
 						},
 					},
 					{

octo/descriptor.go

@@ -89,6 +89,11 @@ type Package struct {
 	IncludeDependencies bool `yaml:"include_dependencies"`
 	Register            bool
 	RegistryToken       string `yaml:"registry_token"`
+	Platform            *Platform
+}
+
+type Platform struct {
+	OS string
 }
 
 type Test struct {