var (
	// ErrNotSupported indicates that a feature is not supported.
	//
	// It is returned by ResponseController methods to indicate that
	// the handler does not support the method, and by the Push method
	// of Pusher implementations to indicate that HTTP/2 Push support
	// is not available.
	ErrNotSupported = &ProtocolError{"feature not supported"}

	// Deprecated: ErrUnexpectedTrailer is no longer returned by

// frameworkImpl.
type extensionPoint struct {
	// the set of plugins to be configured at this extension point.
	plugins *config.PluginSet
	// a pointer to the slice storing plugins implementations that will run at this
	// extension point.
	slicePtr interface{}
}

func (f *frameworkImpl) getExtensionPoints(plugins *config.Plugins) []extensionPoint {
	return []extensionPoint{

		// Remove cached version info.
		xremove(pathf("%s/VERSION.cache", goroot))

		// Remove distribution packages.
		xremoveall(pathf("%s/pkg/distpack", goroot))
	}
}

/*
 * command implementations
 */

// The env command prints the default environment.
func cmdenv() {
	path := flag.Bool("p", false, "emit updated PATH")
	plan9 := flag.Bool("9", gohostos == "plan9", "emit plan 9 syntax")

// Use an affinity graph to mark two values which should use the
// same register. This affinity graph will be used to prefer certain
// registers for allocation. This affinity helps eliminate moves that
// are required for phi implementations and helps generate allocations
// for 2-register architectures.

// Note: regalloc generates a not-quite-SSA output. If we have:
//
//             b1: x = ... : AX
//                 x2 = StoreReg x