all tests passing again

parse.go

@@ -15,7 +15,9 @@ import (
 
 // spec represents a command line option
 type spec struct {
-	dest       reflect.Value
+	root       int
+	path       []string // sequence of field names
+	typ        reflect.Type
 	long       string
 	short      string
 	multiple   bool
@@ -27,6 +29,13 @@ type spec struct {
 	boolean    bool
 }
 
+// command represents a named subcommand, or the top-level command
+type command struct {
+	name        string
+	specs       []*spec
+	subcommands []*command
+}
+
 // ErrHelp indicates that -h or --help were provided
 var ErrHelp = errors.New("help requested by user")
 
@@ -79,7 +88,8 @@ type Config struct {
 
 // Parser represents a set of command line options with destination values
 type Parser struct {
-	specs       []*spec
+	cmd         *command
+	roots       []reflect.Value
 	config      Config
 	version     string
 	description string
@@ -102,41 +112,73 @@ type Described interface {
 }
 
 // walkFields calls a function for each field of a struct, recursively expanding struct fields.
-func walkFields(v reflect.Value, visit func(field reflect.StructField, val reflect.Value, owner reflect.Type) bool) {
+func walkFields(t reflect.Type, visit func(field reflect.StructField, owner reflect.Type) bool) {
-	t := v.Type()
 	for i := 0; i < t.NumField(); i++ {
 		field := t.Field(i)
-		val := v.Field(i)
+		expand := visit(field, t)
-		expand := visit(field, val, t)
 		if expand && field.Type.Kind() == reflect.Struct {
-			walkFields(val, visit)
+			walkFields(field.Type, visit)
 		}
 	}
 }
 
 // NewParser constructs a parser from a list of destination structs
 func NewParser(config Config, dests ...interface{}) (*Parser, error) {
+	// first pick a name for the command for use in the usage text
+	var name string
+	switch {
+	case config.Program != "":
+		name = config.Program
+	case len(os.Args) > 0:
+		name = filepath.Base(os.Args[0])
+	default:
+		name = "program"
+	}
+
+	// construct a parser
 	p := Parser{
+		cmd:    &command{name: name},
 		config: config,
 	}
+
+	// make a list of roots
 	for _, dest := range dests {
+		p.roots = append(p.roots, reflect.ValueOf(dest))
+	}
+
+	// process each of the destination values
+	for i, dest := range dests {
+		t := reflect.TypeOf(dest)
+		if t.Kind() != reflect.Ptr {
+			panic(fmt.Sprintf("%s is not a pointer (did you forget an ampersand?)", t))
+		}
+		t = t.Elem()
+
+		cmd, err := cmdFromStruct(name, t, nil, i)
+		if err != nil {
+			return nil, err
+		}
+		p.cmd.specs = append(p.cmd.specs, cmd.specs...)
+
 		if dest, ok := dest.(Versioned); ok {
 			p.version = dest.Version()
 		}
 		if dest, ok := dest.(Described); ok {
 			p.description = dest.Description()
 		}
-		v := reflect.ValueOf(dest)
-		if v.Kind() != reflect.Ptr {
-			panic(fmt.Sprintf("%s is not a pointer (did you forget an ampersand?)", v.Type()))
-		}
-		v = v.Elem()
-		if v.Kind() != reflect.Struct {
-			panic(fmt.Sprintf("%T is not a struct pointer", dest))
 	}
 
+	return &p, nil
+}
+
+func cmdFromStruct(name string, t reflect.Type, path []string, root int) (*command, error) {
+	if t.Kind() != reflect.Struct {
+		panic(fmt.Sprintf("%v is not a struct pointer", t))
+	}
+
+	var cmd command
 	var errs []string
-		walkFields(v, func(field reflect.StructField, val reflect.Value, t reflect.Type) bool {
+	walkFields(t, func(field reflect.StructField, t reflect.Type) bool {
 		// Check for the ignore switch in the tag
 		tag := field.Tag.Get("arg")
 		if tag == "-" {
@@ -149,8 +191,10 @@ func NewParser(config Config, dests ...interface{}) (*Parser, error) {
 		}
 
 		spec := spec{
+			root: root,
+			path: append(path, field.Name),
 			long: strings.ToLower(field.Name),
-				dest: val,
+			typ:  field.Type,
 		}
 
 		help, exists := field.Tag.Lookup("help")
@@ -207,13 +251,27 @@ func NewParser(config Config, dests ...interface{}) (*Parser, error) {
 					} else {
 						spec.env = strings.ToUpper(field.Name)
 					}
+				case key == "subcommand":
+					// decide on a name for the subcommand
+					cmdname := value
+					if cmdname == "" {
+						cmdname = strings.ToLower(field.Name)
+					}
+
+					subcmd, err := cmdFromStruct(cmdname, field.Type, append(path, field.Name), root)
+					if err != nil {
+						errs = append(errs, err.Error())
+						return false
+					}
+
+					cmd.subcommands = append(cmd.subcommands, subcmd)
 				default:
 					errs = append(errs, fmt.Sprintf("unrecognized tag '%s' on field %s", key, tag))
 					return false
 				}
 			}
 		}
-			p.specs = append(p.specs, &spec)
+		cmd.specs = append(cmd.specs, &spec)
 
 		// if this was an embedded field then we already returned true up above
 		return false
@@ -222,14 +280,8 @@ func NewParser(config Config, dests ...interface{}) (*Parser, error) {
 	if len(errs) > 0 {
 		return nil, errors.New(strings.Join(errs, "\n"))
 	}
-	}
+
-	if p.config.Program == "" {
+	return &cmd, nil
-		p.config.Program = "program"
-		if len(os.Args) > 0 {
-			p.config.Program = filepath.Base(os.Args[0])
-		}
-	}
-	return &p, nil
 }
 
 // Parse processes the given command line option, storing the results in the field
@@ -249,12 +301,12 @@ func (p *Parser) Parse(args []string) error {
 	}
 
 	// Process all command line arguments
-	return process(p.specs, args)
+	return p.process(p.cmd.specs, args)
 }
 
 // process goes through arguments one-by-one, parses them, and assigns the result to
 // the underlying struct field
-func process(specs []*spec, args []string) error {
+func (p *Parser) process(specs []*spec, args []string) error {
 	// track the options we have seen
 	wasPresent := make(map[*spec]bool)
 
@@ -294,7 +346,7 @@ func process(specs []*spec, args []string) error {
 					err,
 				)
 			}
-			if err = setSlice(spec.dest, values, !spec.separate); err != nil {
+			if err = setSlice(p.settable(spec), values, !spec.separate); err != nil {
 				return fmt.Errorf(
 					"error processing environment variable %s with multiple values: %v",
 					spec.env,
@@ -302,7 +354,7 @@ func process(specs []*spec, args []string) error {
 				)
 			}
 		} else {
-			if err := scalar.ParseValue(spec.dest, value); err != nil {
+			if err := scalar.ParseValue(p.settable(spec), value); err != nil {
 				return fmt.Errorf("error processing environment variable %s: %v", spec.env, err)
 			}
 		}
@@ -355,7 +407,7 @@ func process(specs []*spec, args []string) error {
 			} else {
 				values = append(values, value)
 			}
-			err := setSlice(spec.dest, values, !spec.separate)
+			err := setSlice(p.settable(spec), values, !spec.separate)
 			if err != nil {
 				return fmt.Errorf("error processing %s: %v", arg, err)
 			}
@@ -373,14 +425,14 @@ func process(specs []*spec, args []string) error {
 			if i+1 == len(args) {
 				return fmt.Errorf("missing value for %s", arg)
 			}
-			if !nextIsNumeric(spec.dest.Type(), args[i+1]) && isFlag(args[i+1]) {
+			if !nextIsNumeric(spec.typ, args[i+1]) && isFlag(args[i+1]) {
 				return fmt.Errorf("missing value for %s", arg)
 			}
 			value = args[i+1]
 			i++
 		}
 
-		err := scalar.ParseValue(spec.dest, value)
+		err := scalar.ParseValue(p.settable(spec), value)
 		if err != nil {
 			return fmt.Errorf("error processing %s: %v", arg, err)
 		}
@@ -396,13 +448,13 @@ func process(specs []*spec, args []string) error {
 		}
 		wasPresent[spec] = true
 		if spec.multiple {
-			err := setSlice(spec.dest, positionals, true)
+			err := setSlice(p.settable(spec), positionals, true)
 			if err != nil {
 				return fmt.Errorf("error processing %s: %v", spec.long, err)
 			}
 			positionals = nil
 		} else {
-			err := scalar.ParseValue(spec.dest, positionals[0])
+			err := scalar.ParseValue(p.settable(spec), positionals[0])
 			if err != nil {
 				return fmt.Errorf("error processing %s: %v", spec.long, err)
 			}
@@ -445,6 +497,44 @@ func isFlag(s string) bool {
 	return strings.HasPrefix(s, "-") && strings.TrimLeft(s, "-") != ""
 }
 
+func (p *Parser) get(spec *spec) reflect.Value {
+	v := p.roots[spec.root]
+	for _, field := range spec.path {
+		if v.Kind() == reflect.Ptr {
+			if v.IsNil() {
+				return reflect.Value{}
+			}
+			v = v.Elem()
+		}
+
+		v = v.FieldByName(field)
+		if !v.IsValid() {
+			panic(fmt.Errorf("error resolving path %v: %v has no field named %v",
+				spec.path, v.Type(), field))
+		}
+	}
+	return v
+}
+
+func (p *Parser) settable(spec *spec) reflect.Value {
+	v := p.roots[spec.root]
+	for _, field := range spec.path {
+		if v.Kind() == reflect.Ptr {
+			if v.IsNil() {
+				v.Set(reflect.New(v.Type().Elem()))
+			}
+			v = v.Elem()
+		}
+
+		v = v.FieldByName(field)
+		if !v.IsValid() {
+			panic(fmt.Errorf("error resolving path %v: %v has no field named %v",
+				spec.path, v.Type(), field))
+		}
+	}
+	return v
+}
+
 // parse a value as the appropriate type and store it in the struct
 func setSlice(dest reflect.Value, values []string, trunc bool) error {
 	if !dest.CanSet() {

usage.go

@@ -22,7 +22,7 @@ func (p *Parser) Fail(msg string) {
 // WriteUsage writes usage information to the given writer
 func (p *Parser) WriteUsage(w io.Writer) {
 	var positionals, options []*spec
-	for _, spec := range p.specs {
+	for _, spec := range p.cmd.specs {
 		if spec.positional {
 			positionals = append(positionals, spec)
 		} else {
@@ -34,7 +34,7 @@ func (p *Parser) WriteUsage(w io.Writer) {
 		fmt.Fprintln(w, p.version)
 	}
 
-	fmt.Fprintf(w, "Usage: %s", p.config.Program)
+	fmt.Fprintf(w, "Usage: %s", p.cmd.name)
 
 	// write the option component of the usage message
 	for _, spec := range options {
@@ -72,7 +72,7 @@ func (p *Parser) WriteUsage(w io.Writer) {
 // WriteHelp writes the usage string followed by the full help string for each option
 func (p *Parser) WriteHelp(w io.Writer) {
 	var positionals, options []*spec
-	for _, spec := range p.specs {
+	for _, spec := range p.cmd.specs {
 		if spec.positional {
 			positionals = append(positionals, spec)
 		} else {
@@ -106,17 +106,17 @@ func (p *Parser) WriteHelp(w io.Writer) {
 	// write the list of options
 	fmt.Fprint(w, "\nOptions:\n")
 	for _, spec := range options {
-		printOption(w, spec)
+		p.printOption(w, spec)
 	}
 
 	// write the list of built in options
-	printOption(w, &spec{boolean: true, long: "help", short: "h", help: "display this help and exit"})
+	p.printOption(w, &spec{boolean: true, long: "help", short: "h", help: "display this help and exit", root: -1})
 	if p.version != "" {
-		printOption(w, &spec{boolean: true, long: "version", help: "display version and exit"})
+		p.printOption(w, &spec{boolean: true, long: "version", help: "display version and exit", root: -1})
 	}
 }
 
-func printOption(w io.Writer, spec *spec) {
+func (p *Parser) printOption(w io.Writer, spec *spec) {
 	left := "  " + synopsis(spec, "--"+spec.long)
 	if spec.short != "" {
 		left += ", " + synopsis(spec, "-"+spec.short)
@@ -131,7 +131,10 @@ func printOption(w io.Writer, spec *spec) {
 		fmt.Fprint(w, spec.help)
 	}
 	// If spec.dest is not the zero value then a default value has been added.
-	v := spec.dest
+	var v reflect.Value
+	if spec.root >= 0 {
+		v = p.get(spec)
+	}
 	if v.IsValid() {
 		z := reflect.Zero(v.Type())
 		if (v.Type().Comparable() && z.Type().Comparable() && v.Interface() != z.Interface()) || v.Kind() == reflect.Slice && !v.IsNil() {