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