Target data: populate os/arch as well as distro information

Fixes #1371

Signed-off-by: Natalie Arellano <narellano@vmware.com>

platform/target_data.go

@@ -1,6 +1,8 @@
 package platform
 
 import (
+	"runtime"
+
 	"github.com/buildpacks/imgutil"
 
 	"github.com/buildpacks/lifecycle/buildpack"
@@ -87,10 +89,16 @@ func matches(target1, target2 string) bool {
 	return target1 == target2
 }
 
-// GetTargetOSFromFileSystem populates the target metadata you pass in if the information is available
-// returns a boolean indicating whether it populated any data.
+// GetTargetOSFromFileSystem populates the provided target metadata with information from /etc/os-release
+// if it is available.
 func GetTargetOSFromFileSystem(d fsutil.Detector, tm *files.TargetMetadata, logger log.Logger) {
 	if d.HasSystemdFile() {
+		if tm.OS == "" {
+			tm.OS = "linux"
+		}
+		if tm.Arch == "" {
+			tm.Arch = runtime.GOARCH // in a future world where we support cross platform builds, this should be removed
+		}
 		contents, err := d.ReadSystemdFile()
 		if err != nil {
 			logger.Warnf("Encountered error trying to read /etc/os-release file: %s", err.Error())

platform/target_data_test.go

@@ -2,6 +2,7 @@ package platform_test
 
 import (
 	"fmt"
+	"runtime"
 	"testing"
 
 	"github.com/apex/log"
@@ -129,6 +130,8 @@ func testTargetData(t *testing.T, when spec.G, it spec.S) {
 				t:       t,
 				HasFile: true}
 			platform.GetTargetOSFromFileSystem(&d, &tm, logr)
+			h.AssertEq(t, "linux", tm.OS)
+			h.AssertEq(t, runtime.GOARCH, tm.Arch)
 			h.AssertEq(t, "opensesame", tm.Distro.Name)
 			h.AssertEq(t, "3.14", tm.Distro.Version)
 		})