system prune: delegate version check

Move the version-check for pruners to the pruner, which can
return a [ErrNotImplemented] error to indicate they won't
be run with the API version that's used.

This helps separating concerns, and doesn't enforce knowledge
about what's supported by each content-type onto the system
prune command.

[ErrNotImplemented]: https://pkg.go.dev/github.com/docker/docker@v28.3.3+incompatible/errdefs#ErrNotImplemented

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

cli/command/builder/prune.go

@@ -14,6 +14,7 @@ import (
 	"github.com/docker/cli/opts"
 	"github.com/docker/go-units"
 	"github.com/moby/moby/api/types/build"
+	"github.com/moby/moby/api/types/versions"
 	"github.com/spf13/cobra"
 )
 
@@ -112,6 +113,10 @@ type cancelledErr struct{ error }
 
 func (cancelledErr) Cancelled() {}
 
+type errNotImplemented struct{ error }
+
+func (errNotImplemented) NotImplemented() {}
+
 // CachePrune executes a prune command for build cache
 //
 // Deprecated: this function was only used internally and will be removed in the next release.
@@ -122,6 +127,10 @@ func CachePrune(ctx context.Context, dockerCli command.Cli, all bool, filter opt
 // pruneFn prunes the build cache for use in "docker system prune" and
 // returns the amount of space reclaimed and a detailed output string.
 func pruneFn(ctx context.Context, dockerCLI command.Cli, options pruner.PruneOptions) (uint64, string, error) {
+	if ver := dockerCLI.Client().ClientVersion(); ver != "" && versions.LessThan(ver, "1.31") {
+		// Not supported on older daemons.
+		return 0, "", errNotImplemented{errors.New("builder prune requires API version 1.31 or greater")}
+	}
 	if !options.Confirmed {
 		// Dry-run: perform validation and produce confirmation before pruning.
 		var confirmMsg string

cli/command/system/prune.go

@@ -17,16 +17,14 @@ import (
 	"github.com/docker/cli/opts"
 	"github.com/docker/go-units"
 	"github.com/fvbommel/sortorder"
-	"github.com/moby/moby/api/types/versions"
 	"github.com/spf13/cobra"
 )
 
 type pruneOptions struct {
-	force           bool
-	all             bool
-	pruneVolumes    bool
-	pruneBuildCache bool
-	filter          opts.FilterOpt
+	force        bool
+	all          bool
+	pruneVolumes bool
+	filter       opts.FilterOpt
 }
 
 // newPruneCommand creates a new cobra.Command for `docker prune`
@@ -38,7 +36,6 @@ func newPruneCommand(dockerCli command.Cli) *cobra.Command {
 		Short: "Remove unused data",
 		Args:  cli.NoArgs,
 		RunE: func(cmd *cobra.Command, args []string) error {
-			options.pruneBuildCache = versions.GreaterThanOrEqualTo(dockerCli.Client().ClientVersion(), "1.31")
 			return runPrune(cmd.Context(), dockerCli, options)
 		},
 		Annotations:       map[string]string{"version": "1.25"},
@@ -95,11 +92,7 @@ func runPrune(ctx context.Context, dockerCli command.Cli, options pruneOptions)
 			if !options.pruneVolumes {
 				continue
 			}
-		case pruner.TypeBuildCache:
-			if !options.pruneBuildCache {
-				continue
-			}
-		case pruner.TypeContainer, pruner.TypeNetwork, pruner.TypeImage:
+		case pruner.TypeContainer, pruner.TypeNetwork, pruner.TypeImage, pruner.TypeBuildCache:
 			// no special handling; keeping the "exhaustive" linter happy.
 		default:
 			// other pruners; no special handling; keeping the "exhaustive" linter happy.
@@ -110,7 +103,7 @@ func runPrune(ctx context.Context, dockerCli command.Cli, options pruneOptions)
 			All:       options.all,
 			Filter:    options.filter,
 		})
-		if err != nil {
+		if err != nil && !errdefs.IsNotImplemented(err) {
 			return err
 		}
 		spaceReclaimed += spc
@@ -141,10 +134,10 @@ func dryRun(ctx context.Context, dockerCli command.Cli, options pruneOptions) (s
 			if !options.pruneVolumes {
 				continue
 			}
-		case pruner.TypeBuildCache:
-			if !options.pruneBuildCache {
-				continue
-			}
+		case pruner.TypeContainer, pruner.TypeNetwork, pruner.TypeImage, pruner.TypeBuildCache:
+			// no special handling; keeping the "exhaustive" linter happy.
+		default:
+			// other pruners; no special handling; keeping the "exhaustive" linter happy.
 		}
 		// Always run with "[pruner.PruneOptions.Confirmed] = false"
 		// to perform validation of the given options and produce
@@ -155,7 +148,7 @@ func dryRun(ctx context.Context, dockerCli command.Cli, options pruneOptions) (s
 		})
 		// A "canceled" error is expected in dry-run mode; any other error
 		// must be returned as a "fatal" error.
-		if err != nil && !errdefs.IsCanceled(err) {
+		if err != nil && !errdefs.IsCanceled(err) && !errdefs.IsNotImplemented(err) {
 			errs = append(errs, err)
 		}
 		if confirmMsg != "" {

cli/command/system/pruner/pruner.go

@@ -50,9 +50,10 @@ var pruneOrder = []ContentType{
 //     will be pruned (for example, "all stopped containers") instead of
 //     executing the prune. This summary is presented to the user as a
 //     confirmation message. It may return a [ErrCancelled] to indicate
-//     the operation was canceled. Any other error is considered a
-//     validation error of the given options (such as a filter that
-//     is not supported.
+//     the operation was canceled or a [ErrNotImplemented] if the prune
+//     function is not implemented for the daemon's API version. Any
+//     other error is considered a validation error for the given options
+//     (such as a filter that is not supported).
 //   - If [PruneOptions.Confirmed] is "true", the PruneFunc must execute
 //     the prune with the given options.
 //
@@ -64,6 +65,7 @@ var pruneOrder = []ContentType{
 //     presented to the user.
 //
 // [ErrCancelled]: https://pkg.go.dev/github.com/docker/docker@v28.3.3+incompatible/errdefs#ErrCancelled
+// [ErrNotImplemented]: https://pkg.go.dev/github.com/docker/docker@v28.3.3+incompatible/errdefs#ErrNotImplemented
 type PruneFunc func(ctx context.Context, dockerCLI command.Cli, pruneOpts PruneOptions) (spaceReclaimed uint64, details string, _ error)
 
 type PruneOptions struct {