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options.go
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options.go
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package kong
import (
"io"
"os"
"os/user"
"path/filepath"
"reflect"
"strings"
"github.com/pkg/errors"
)
// An Option applies optional changes to the Kong application.
type Option interface {
Apply(k *Kong) error
}
// OptionFunc is function that adheres to the Option interface.
type OptionFunc func(k *Kong) error
func (o OptionFunc) Apply(k *Kong) error { return o(k) } // nolint: golint
// Vars sets the variables to use for interpolation into help strings and default values.
//
// See README for details.
type Vars map[string]string
// Apply lets Vars act as an Option.
func (v Vars) Apply(k *Kong) error {
for key, value := range v {
k.vars[key] = value
}
return nil
}
// CloneWith clones the current Vars and merges "vars" onto the clone.
func (v Vars) CloneWith(vars Vars) Vars {
out := make(Vars, len(v)+len(vars))
for key, value := range v {
out[key] = value
}
for key, value := range vars {
out[key] = value
}
return out
}
// Exit overrides the function used to terminate. This is useful for testing or interactive use.
func Exit(exit func(int)) Option {
return OptionFunc(func(k *Kong) error {
k.Exit = exit
return nil
})
}
// NoDefaultHelp disables the default help flags.
func NoDefaultHelp() Option {
return OptionFunc(func(k *Kong) error {
k.noDefaultHelp = true
return nil
})
}
// PostBuild provides read/write access to kong.Kong after initial construction of the model is complete but before
// parsing occurs.
//
// This is useful for, e.g., adding short options to flags, updating help, etc.
func PostBuild(fn func(*Kong) error) Option {
return OptionFunc(func(k *Kong) error {
k.postBuildOptions = append(k.postBuildOptions, OptionFunc(fn))
return nil
})
}
// Name overrides the application name.
func Name(name string) Option {
return PostBuild(func(k *Kong) error {
k.Model.Name = name
return nil
})
}
// Description sets the application description.
func Description(description string) Option {
return PostBuild(func(k *Kong) error {
k.Model.Help = description
return nil
})
}
// TypeMapper registers a mapper to a type.
func TypeMapper(typ reflect.Type, mapper Mapper) Option {
return OptionFunc(func(k *Kong) error {
k.registry.RegisterType(typ, mapper)
return nil
})
}
// KindMapper registers a mapper to a kind.
func KindMapper(kind reflect.Kind, mapper Mapper) Option {
return OptionFunc(func(k *Kong) error {
k.registry.RegisterKind(kind, mapper)
return nil
})
}
// ValueMapper registers a mapper to a field value.
func ValueMapper(ptr interface{}, mapper Mapper) Option {
return OptionFunc(func(k *Kong) error {
k.registry.RegisterValue(ptr, mapper)
return nil
})
}
// NamedMapper registers a mapper to a name.
func NamedMapper(name string, mapper Mapper) Option {
return OptionFunc(func(k *Kong) error {
k.registry.RegisterName(name, mapper)
return nil
})
}
// Writers overrides the default writers. Useful for testing or interactive use.
func Writers(stdout, stderr io.Writer) Option {
return OptionFunc(func(k *Kong) error {
k.Stdout = stdout
k.Stderr = stderr
return nil
})
}
// Bind binds values for hooks and Run() function arguments.
//
// Any arguments passed will be available to the receiving hook functions, but may be omitted. Additionally, *Kong and
// the current *Context will also be made available.
//
// There are two hook points:
//
// BeforeApply(...) error
// AfterApply(...) error
//
// Called before validation/assignment, and immediately after validation/assignment, respectively.
func Bind(args ...interface{}) Option {
return OptionFunc(func(k *Kong) error {
k.bindings.add(args...)
return nil
})
}
// BindTo allows binding of implementations to interfaces.
//
// BindTo(impl, (*iface)(nil))
func BindTo(impl, iface interface{}) Option {
return OptionFunc(func(k *Kong) error {
valueOf := reflect.ValueOf(impl)
k.bindings[reflect.TypeOf(iface).Elem()] = func() (reflect.Value, error) { return valueOf, nil }
return nil
})
}
// BindToProvider allows binding of provider functions.
//
// This is useful when the Run() function of different commands require different values that may
// not all be initialisable from the main() function.
func BindToProvider(provider interface{}) Option {
return OptionFunc(func(k *Kong) error {
pv := reflect.ValueOf(provider)
t := pv.Type()
if t.Kind() != reflect.Func || t.NumIn() != 0 || t.NumOut() != 2 || t.Out(1) != reflect.TypeOf((*error)(nil)).Elem() {
return errors.Errorf("%T must be a function with the signature func()(T, error)", provider)
}
rt := pv.Type().Out(0)
k.bindings[rt] = func() (reflect.Value, error) {
out := pv.Call(nil)
errv := out[1]
var err error
if !errv.IsNil() {
err = errv.Interface().(error)
}
return out[0], err
}
return nil
})
}
// Help printer to use.
func Help(help HelpPrinter) Option {
return OptionFunc(func(k *Kong) error {
k.help = help
return nil
})
}
// HelpFormatter configures how the help text is formatted.
func HelpFormatter(helpFormatter HelpValueFormatter) Option {
return OptionFunc(func(k *Kong) error {
k.helpFormatter = helpFormatter
return nil
})
}
// ConfigureHelp sets the HelpOptions to use for printing help.
func ConfigureHelp(options HelpOptions) Option {
return OptionFunc(func(k *Kong) error {
k.helpOptions = options
return nil
})
}
// UsageOnError configures Kong to display context-sensitive usage if FatalIfErrorf is called with an error.
func UsageOnError() Option {
return OptionFunc(func(k *Kong) error {
k.usageOnError = true
return nil
})
}
// ClearResolvers clears all existing resolvers.
func ClearResolvers() Option {
return OptionFunc(func(k *Kong) error {
k.resolvers = nil
return nil
})
}
// Resolvers registers flag resolvers.
func Resolvers(resolvers ...Resolver) Option {
return OptionFunc(func(k *Kong) error {
k.resolvers = append(k.resolvers, resolvers...)
return nil
})
}
// ConfigurationLoader is a function that builds a resolver from a file.
type ConfigurationLoader func(r io.Reader) (Resolver, error)
// Configuration provides Kong with support for loading defaults from a set of configuration files.
//
// Paths will be opened in order, and "loader" will be used to provide a Resolver which is registered with Kong.
//
// Note: The JSON function is a ConfigurationLoader.
//
// ~ and variable expansion will occur on the provided paths.
func Configuration(loader ConfigurationLoader, paths ...string) Option {
return OptionFunc(func(k *Kong) error {
k.loader = loader
for _, path := range paths {
if _, err := os.Stat(ExpandPath(path)); os.IsNotExist(err) {
continue
}
resolver, err := k.LoadConfig(path)
if err != nil {
return errors.Wrap(err, path)
}
if resolver != nil {
k.resolvers = append(k.resolvers, resolver)
}
}
return nil
})
}
// ExpandPath is a helper function to expand a relative or home-relative path to an absolute path.
//
// eg. ~/.someconf -> /home/alec/.someconf
func ExpandPath(path string) string {
if filepath.IsAbs(path) {
return path
}
if strings.HasPrefix(path, "~/") {
user, err := user.Current()
if err != nil {
return path
}
return filepath.Join(user.HomeDir, path[2:])
}
abspath, err := filepath.Abs(path)
if err != nil {
return path
}
return abspath
}