Add describe changed command to check if a package needs rebuild

cmd/describe-changed.go

@@ -0,0 +1,102 @@
+package cmd
+
+import (
+	"context"
+	"fmt"
+	"os"
+	"path/filepath"
+
+	log "github.com/sirupsen/logrus"
+	"github.com/spf13/cobra"
+
+	"github.com/gitpod-io/leeway/pkg/leeway"
+	"github.com/gitpod-io/leeway/pkg/leeway/cache"
+	"github.com/gitpod-io/leeway/pkg/leeway/cache/local"
+)
+
+const (
+	// ExitChangedUnchanged indicates the package is cached and does not need a rebuild.
+	ExitChangedUnchanged = 0
+	// ExitChangedNeedsRebuild indicates the package has changed and needs a rebuild.
+	ExitChangedNeedsRebuild = 1
+	// ExitChangedError indicates an error occurred while checking.
+	ExitChangedError = 2
+)
+
+// describeChangedCmd checks whether a package has changed by looking up its
+// current version hash in the local and remote caches. If the version exists
+// in either cache the package is unchanged (exit 0); otherwise it has changed
+// and needs a rebuild (exit 1). Errors exit with code 2.
+var describeChangedCmd = &cobra.Command{
+	Use:   "changed <package>",
+	Short: "Checks whether a package needs to be rebuilt by consulting the cache",
+	Long: `Computes the version hash of a package and checks whether a build artifact
+for that version already exists in the local or remote cache.
+
+Exit codes:
+  0 - package is cached (unchanged, no rebuild needed)
+  1 - package is not cached (changed, needs rebuild)
+  2 - an error occurred
+
+This is useful for CI branching decisions:
+
+  if leeway describe changed my-component:my-package; then
+    echo "unchanged, skipping build"
+  else
+    echo "changed, rebuilding"
+    leeway build my-component:my-package
+  fi`,
+	Args: cobra.ExactArgs(1),
+	Run: func(cmd *cobra.Command, args []string) {
+		_, pkg, _, exists := getTarget(args, false)
+		if !exists {
+			os.Exit(ExitChangedError)
+		}
+		if pkg == nil {
+			log.Error("changed requires a package, not a component")
+			os.Exit(ExitChangedError)
+		}
+
+		version, err := pkg.Version()
+		if err != nil {
+			log.WithError(err).Error("cannot compute package version")
+			os.Exit(ExitChangedError)
+		}
+
+		// Check local cache
+		localCacheLoc := os.Getenv(leeway.EnvvarCacheDir)
+		if localCacheLoc == "" {
+			localCacheLoc = filepath.Join(os.TempDir(), "leeway", "cache")
+		}
+		localCache, err := local.NewFilesystemCache(localCacheLoc)
+		if err != nil {
+			log.WithError(err).Error("cannot set up local cache")
+			os.Exit(ExitChangedError)
+		}
+
+		if _, found := localCache.Location(pkg); found {
+			fmt.Printf("%s\t%s\tcached locally\n", pkg.FullName(), version)
+			os.Exit(ExitChangedUnchanged)
+		}
+
+		// Check remote cache
+		remoteCache := getRemoteCacheFromEnv()
+		remote, err := remoteCache.ExistingPackages(context.Background(), []cache.Package{pkg})
+		if err != nil {
+			log.WithError(err).Error("cannot check remote cache")
+			os.Exit(ExitChangedError)
+		}
+
+		if _, found := remote[pkg]; found {
+			fmt.Printf("%s\t%s\tcached remotely\n", pkg.FullName(), version)
+			os.Exit(ExitChangedUnchanged)
+		}
+
+		fmt.Printf("%s\t%s\tchanged\n", pkg.FullName(), version)
+		os.Exit(ExitChangedNeedsRebuild)
+	},
+}
+
+func init() {
+	describeCmd.AddCommand(describeChangedCmd)
+}