Add some logging to dep prune

cmd/dep/prune.go

@@ -7,6 +7,7 @@ package main
 import (
 	"bytes"
 	"flag"
+	"log"
 
 	"github.com/golang/dep"
 	"github.com/golang/dep/internal/gps"
@@ -75,5 +76,9 @@ func (cmd *pruneCommand) Run(ctx *dep.Ctx, args []string) error {
 		return errors.Errorf("lock hash doesn't match")
 	}
 
-	return dep.PruneProject(p, sm)
+	var pruneLogger *log.Logger
+	if ctx.Loggers.Verbose {
+		pruneLogger = ctx.Loggers.Err
+	}
+	return dep.PruneProject(p, sm, pruneLogger)
 }

txn_writer.go

@@ -495,7 +495,7 @@ func (sw *SafeWriter) PrintPreparedActions(output *log.Logger) error {
 	return nil
 }
 
-func PruneProject(p *Project, sm gps.SourceManager) error {
+func PruneProject(p *Project, sm gps.SourceManager, logger *log.Logger) error {
 	td, err := ioutil.TempDir(os.TempDir(), "dep")
 	if err != nil {
 		return errors.Wrap(err, "error while creating temp dir for writing manifest/lock/vendor")
@@ -514,11 +514,20 @@ func PruneProject(p *Project, sm gps.SourceManager) error {
 		}
 	}
 
-	toDelete, err := calculatePrune(td, toKeep)
+	toDelete, err := calculatePrune(td, toKeep, logger)
 	if err != nil {
 		return err
 	}
 
+	if logger != nil {
+		if len(toDelete) > 0 {
+			logger.Println("Calculated the following directories to prune:")
+			for _, d := range toDelete {
+				logger.Printf("  %s", d)
+			}
+		}
+	}
+
 	if err := deleteDirs(toDelete); err != nil {
 		return err
 	}
@@ -556,7 +565,10 @@ fail:
 	return failerr
 }
 
-func calculatePrune(vendorDir string, keep []string) ([]string, error) {
+func calculatePrune(vendorDir string, keep []string, logger *log.Logger) ([]string, error) {
+	if logger != nil {
+		logger.Println("Calculating prune. Checking the following packages:")
+	}
 	sort.Strings(keep)
 	toDelete := []string{}
 	err := filepath.Walk(vendorDir, func(path string, info os.FileInfo, err error) error {
@@ -571,6 +583,9 @@ func calculatePrune(vendorDir string, keep []string) ([]string, error) {
 		}
 
 		name := strings.TrimPrefix(path, vendorDir+"/")
+		if logger != nil {
+			logger.Printf("  %s", name)
+		}
 		i := sort.Search(len(keep), func(i int) bool {
 			return name <= keep[i]
 		})