[17.06] backport (cli) Don't prune volumes on docker system prune

components/cli/cli/command/system/prune.go

@@ -1,7 +1,9 @@
 package system
 
 import (
+	"bytes"
 	"fmt"
+	"text/template"
 
 	"github.com/docker/cli/cli"
 	"github.com/docker/cli/cli/command"
@@ -12,9 +14,10 @@ import (
 )
 
 type pruneOptions struct {
-	force  bool
-	all    bool
-	filter opts.FilterOpt
+	force        bool
+	all          bool
+	pruneVolumes bool
+	filter       opts.FilterOpt
 }
 
 // NewPruneCommand creates a new cobra.Command for `docker prune`
@@ -34,45 +37,35 @@ func NewPruneCommand(dockerCli command.Cli) *cobra.Command {
 	flags := cmd.Flags()
 	flags.BoolVarP(&options.force, "force", "f", false, "Do not prompt for confirmation")
 	flags.BoolVarP(&options.all, "all", "a", false, "Remove all unused images not just dangling ones")
+	flags.BoolVar(&options.pruneVolumes, "volumes", false, "Prune volumes")
 	flags.Var(&options.filter, "filter", "Provide filter values (e.g. 'label=<key>=<value>')")
 	// "filter" flag is available in 1.28 (docker 17.04) and up
 	flags.SetAnnotation("filter", "version", []string{"1.28"})
 
 	return cmd
 }
 
-const (
-	warning = `WARNING! This will remove:
-	- all stopped containers
-	- all volumes not used by at least one container
-	- all networks not used by at least one container
-	%s
+const confirmationTemplate = `WARNING! This will remove:
+{{- range $_, $warning := . }}
+        - {{ $warning }}
+{{- end }}
 Are you sure you want to continue?`
 
-	danglingImageDesc = "- all dangling images"
-	allImageDesc      = `- all images without at least one container associated to them`
-)
-
 func runPrune(dockerCli command.Cli, options pruneOptions) error {
-	var message string
-
-	if options.all {
-		message = fmt.Sprintf(warning, allImageDesc)
-	} else {
-		message = fmt.Sprintf(warning, danglingImageDesc)
-	}
-
-	if !options.force && !command.PromptForConfirmation(dockerCli.In(), dockerCli.Out(), message) {
+	if !options.force && !command.PromptForConfirmation(dockerCli.In(), dockerCli.Out(), confirmationMessage(options)) {
 		return nil
 	}
 
 	var spaceReclaimed uint64
-
-	for _, pruneFn := range []func(dockerCli command.Cli, filter opts.FilterOpt) (uint64, string, error){
+	pruneFuncs := []func(dockerCli command.Cli, filter opts.FilterOpt) (uint64, string, error){
 		prune.RunContainerPrune,
-		prune.RunVolumePrune,
 		prune.RunNetworkPrune,
-	} {
+	}
+	if options.pruneVolumes {
+		pruneFuncs = append(pruneFuncs, prune.RunVolumePrune)
+	}
+
+	for _, pruneFn := range pruneFuncs {
 		spc, output, err := pruneFn(dockerCli, options.filter)
 		if err != nil {
 			return err
@@ -96,3 +89,26 @@ func runPrune(dockerCli command.Cli, options pruneOptions) error {
 
 	return nil
 }
+
+// confirmationMessage constructs a confirmation message that depends on the cli options.
+func confirmationMessage(options pruneOptions) string {
+	t := template.Must(template.New("confirmation message").Parse(confirmationTemplate))
+
+	warnings := []string{
+		"all stopped containers",
+		"all networks not used by at least one container",
+	}
+	if options.pruneVolumes {
+		warnings = append(warnings, "all volumes not used by at least one container")
+	}
+	if options.all {
+		warnings = append(warnings, "all images without at least one container associated to them")
+	} else {
+		warnings = append(warnings, "all dangling images")
+	}
+	warnings = append(warnings, "all build cache")
+
+	var buffer bytes.Buffer
+	t.Execute(&buffer, &warnings)
+	return buffer.String()
+}