command: hard wrap help message flags

This greatly improves readability when lots of flags are registered.

Signed-off-by: Ophestra <cat@gensokyo.uk>

command/builder.go

@@ -23,8 +23,8 @@ func newNode(output io.Writer, logf LogFunc, name, usage string) *node {
 	n.set.SetOutput(output)
 	n.set.Usage = func() {
 		_ = n.writeHelp()
-		if n.suffix.Len() > 0 {
-			_, _ = fmt.Fprintln(output, "Flags:")
+		if len(n.suffix) > 0 {
+			_, _ = fmt.Fprintln(output, "flags:")
 			n.set.PrintDefaults()
 			_, _ = fmt.Fprintln(output)
 		}

command/flag.go

@@ -16,7 +16,13 @@ func (e FlagError) Is(target error) bool {
 }
 
 func (n *node) Flag(p any, name string, value FlagDefiner, usage string) Node {
-	value.Define(&n.suffix, n.set, p, name, usage)
+	var buf strings.Builder
+	value.Define(&buf, n.set, p, name, usage)
+	s := buf.String()
+	if len(s) > 0 && s[0] == ' ' {
+		s = s[1:]
+	}
+	n.suffix = append(n.suffix, s)
 	return n
 }
 

command/help.go

@@ -1,6 +1,7 @@
 package command
 
 import (
+	"bytes"
 	"errors"
 	"fmt"
 	"io"
@@ -13,14 +14,31 @@ var ErrHelp = errors.New("help requested")
 func (n *node) PrintHelp() { _ = n.writeHelp() }
 
 func (n *node) writeHelp() error {
+	prefix := strings.Join(append(n.prefix, n.name), " ")
+	var buf strings.Builder
+	offset := 7 + len(prefix)
+	line := offset + 14
+	w := bytes.Repeat([]byte{' '}, offset+1)
+	w[0] = '\n'
+
+	for _, flag := range n.suffix {
+		line += len(flag) + 1
+		if line >= 80 {
+			line = offset + len(flag) + 1
+			buf.Write(w)
+		}
+		buf.WriteByte(' ')
+		buf.WriteString(flag)
+	}
+
 	if _, err := fmt.Fprintf(n.out,
-		"\nUsage:\t%s [-h | --help]%s COMMAND [OPTIONS]\n",
-		strings.Join(append(n.prefix, n.name), " "), &n.suffix,
+		"usage: %s [-h | --help]%s <command> [<args>]\n",
+		prefix, &buf,
 	); err != nil {
 		return err
 	}
 	if n.child != nil {
-		if _, err := fmt.Fprint(n.out, "\nCommands:\n"); err != nil {
+		if _, err := fmt.Fprint(n.out, "\ncommands:\n"); err != nil {
 			return err
 		}
 	}

command/node.go

@@ -3,7 +3,6 @@ package command
 import (
 	"flag"
 	"io"
-	"strings"
 )
 
 // A node represents a command.
@@ -17,7 +16,7 @@ type node struct {
 	// Names of commands preceding node.
 	prefix []string
 	// Short user-facing representations of flags received by node.
-	suffix strings.Builder
+	suffix []string
 
 	f   HandlerFunc
 	set *flag.FlagSet

command/parse_test.go

@@ -70,7 +70,7 @@ func TestParse(t *testing.T) {
 			"d=0 out of order string flag",
 			buildTestCommand,
 			[]string{"string", "--string", "64d3b4b7b21788585845060e2199a78f"},
-			"flag provided but not defined: -string\n\nUsage:\ttest string [-h | --help] COMMAND [OPTIONS]\n\n", "",
+			"flag provided but not defined: -string\nusage: test string [-h | --help] <command> [<args>]\n\n", "",
 			errors.New("flag provided but not defined: -string"),
 		},
 		{
@@ -120,7 +120,7 @@ func TestParse(t *testing.T) {
 			"d=1 empty sub help",
 			buildTestCommand,
 			[]string{"empty", "-h"},
-			"\nUsage:\ttest empty [-h | --help] COMMAND [OPTIONS]\n\n", "", flag.ErrHelp,
+			"usage: test empty [-h | --help] <command> [<args>]\n\n", "", flag.ErrHelp,
 		},
 		{
 			"d=1 no match",
@@ -151,10 +151,10 @@ func TestParse(t *testing.T) {
 			"d=0 help",
 			buildTestCommand,
 			[]string{},
-			`
-Usage:	test [-h | --help] [-v] [--fail] [--string <value>] [--int <int>] [--repeat <value>] COMMAND [OPTIONS]
+			`usage: test [-h | --help] [-v] [--fail] [--string <value>] [--int <int>]
+            [--repeat <value>] <command> [<args>]
 
-Commands:
+commands:
     error      return an error
     print      wraps Fprint
     string     print string passed by flag
@@ -171,10 +171,10 @@ Commands:
 			"d=0 help flag",
 			buildTestCommand,
 			[]string{"-h"},
-			`
-Usage:	test [-h | --help] [-v] [--fail] [--string <value>] [--int <int>] [--repeat <value>] COMMAND [OPTIONS]
+			`usage: test [-h | --help] [-v] [--fail] [--string <value>] [--int <int>]
+            [--repeat <value>] <command> [<args>]
 
-Commands:
+commands:
     error      return an error
     print      wraps Fprint
     string     print string passed by flag
@@ -185,7 +185,7 @@ Commands:
     succeed    this command succeeds
     deep       top level of command tree with various levels
 
-Flags:
+flags:
   -fail
     	fail early
   -int int
@@ -203,10 +203,9 @@ Flags:
 			"d=1 help",
 			buildTestCommand,
 			[]string{"join"},
-			`
-Usage:	test join [-h | --help] COMMAND [OPTIONS]
+			`usage: test join [-h | --help] <command> [<args>]
 
-Commands:
+commands:
     out    write result to wout
     log    log result to wlog
 
@@ -216,10 +215,9 @@ Commands:
 			"d=1 help flag",
 			buildTestCommand,
 			[]string{"join", "-h"},
-			`
-Usage:	test join [-h | --help] COMMAND [OPTIONS]
+			`usage: test join [-h | --help] <command> [<args>]
 
-Commands:
+commands:
     out    write result to wout
     log    log result to wlog
 
@@ -230,10 +228,9 @@ Commands:
 			"d=2 help",
 			buildTestCommand,
 			[]string{"deep", "d=2"},
-			`
-Usage:	test deep d=2 [-h | --help] COMMAND [OPTIONS]
+			`usage: test deep d=2 [-h | --help] <command> [<args>]
 
-Commands:
+commands:
     d=3    relative third level
 
 `, "", command.ErrHelp,
@@ -242,10 +239,9 @@ Commands:
 			"d=2 help flag",
 			buildTestCommand,
 			[]string{"deep", "d=2", "-h"},
-			`
-Usage:	test deep d=2 [-h | --help] COMMAND [OPTIONS]
+			`usage: test deep d=2 [-h | --help] <command> [<args>]
 
-Commands:
+commands:
     d=3    relative third level
 
 `, "", flag.ErrHelp,
@@ -261,7 +257,7 @@ Commands:
 				t.Errorf("Parse: error = %v; wantErr %v", err, tc.wantErr)
 			}
 			if got := wout.String(); got != tc.want {
-				t.Errorf("Parse: %s want %s", got, tc.want)
+				t.Errorf("Parse:\n%s\nwant\n%s", got, tc.want)
 			}
 			if gotLog := wlog.String(); gotLog != tc.wantLog {
 				t.Errorf("Parse: log = %s wantLog %s", gotLog, tc.wantLog)