Add alias support

Signed-off-by: jolheiser <john.olheiser@gmail.com>

examples/alias/README.md

@@ -0,0 +1,39 @@
+# myapp
+
+myapp
+
+```
+myapp
+```
+
+
+```
+[--bool-flag,-bf]
+[--duration-flag,-df]=[value]
+[--help]
+[--int-flag,-if]=[value]
+[--string-flag,-sf]=[value]
+```
+**Usage**:
+
+```
+myapp [FLAGS] [ARGS...]
+```
+
+**--bool-flag,-bf**: Bool flag
+
+
+**--duration-flag,-df**="": Duration flag
+
+
+**--help**: Show help
+
+
+**--int-flag,-if**="": Int flag
+
+
+**--string-flag,-sf**="": String flag
+
+
+-----
+

examples/alias/main.go

@@ -0,0 +1,48 @@
+//go:build generate
+// +build generate
+
+package main
+
+import (
+	"flag"
+	"github.com/peterbourgon/ff/v3/ffcli"
+	"os"
+
+	"go.jolheiser.com/ffmd"
+)
+
+//go:generate go run main.go
+func main() {
+	fs := flag.NewFlagSet("myapp", flag.ExitOnError)
+	stringFlag := fs.String("string-flag", "", "String flag")
+	fs.StringVar(stringFlag, "sf", *stringFlag, "--string-flag")
+	intFlag := fs.Int("int-flag", 0, "Int flag")
+	fs.IntVar(intFlag, "if", *intFlag, "--int-flag")
+	boolFlag := fs.Bool("bool-flag", false, "Bool flag")
+	fs.BoolVar(boolFlag, "bf", *boolFlag, "--bool-flag")
+	durFlag := fs.Duration("duration-flag", 0, "Duration flag")
+	fs.DurationVar(durFlag, "df", *durFlag, "--duration-flag")
+
+	cmd := &ffcli.Command{
+		Name:        "myapp",
+		FlagSet:     fs,
+		Subcommands: nil,
+	}
+
+	md, err := ffmd.Command(cmd)
+	if err != nil {
+		panic(err)
+	}
+	write("README.md", md)
+}
+
+func write(path, content string) {
+	fi, err := os.Create(path)
+	if err != nil {
+		panic(err)
+	}
+	defer fi.Close()
+	if _, err := fi.WriteString(content); err != nil {
+		panic(err)
+	}
+}

ffmd.go

@@ -3,6 +3,7 @@ package ffmd
 import (
 	"bytes"
 	_ "embed"
+	"errors"
 	"flag"
 	"fmt"
 	"reflect"
@@ -30,6 +31,9 @@ func FlagSet(fs *flag.FlagSet) (string, error) {
 }
 
 func fromCommand(cmd *ffcli.Command, section int) (string, error) {
+	if cmd.FlagSet == nil {
+		return "", errors.New("all commands should have a flagset, even if empty")
+	}
 	c := flagSetCommand(cmd.FlagSet, section)
 	c.Name = cmd.Name
 	c.Usage = fmt.Sprintf("%s [FLAGS] [ARGS...]", cmd.Name)
@@ -77,19 +81,33 @@ func flagSetCommand(fs *flag.FlagSet, section int) command {
 			},
 		},
 	}
+	aliases := make(map[string][]string)
 	fs.VisitAll(func(f *flag.Flag) {
 		_, isBool := f.Value.(boolFlag)
 		def := f.DefValue
 		if isZeroValue(f, def) {
 			def = ""
 		}
-		a.Flags = append(a.Flags, appFlag{
+		af := appFlag{
 			Name:    f.Name,
 			Usage:   f.Usage,
 			Default: def,
 			IsBool:  isBool,
-		})
+		}
+		if strings.HasPrefix(af.Usage, "--") {
+			aliasOf := strings.TrimPrefix(af.Usage, "--")
+			if _, ok := aliases[aliasOf]; !ok {
+				aliases[aliasOf] = make([]string, 0)
+			}
+			aliases[aliasOf] = append(aliases[aliasOf], af.Name)
+			return
+		}
+		a.Flags = append(a.Flags, af)
 	})
+	for idx, f := range a.Flags {
+		f.Aliases = aliases[f.Name]
+		a.Flags[idx] = f
+	}
 	sort.Slice(a.Flags, func(i, j int) bool {
 		return a.Flags[i].Name < a.Flags[j].Name
 	})
@@ -119,11 +137,20 @@ func (c command) Markdown() (string, error) {
 
 type appFlag struct {
 	Name    string
+	Aliases []string
 	Usage   string
 	Default string
 	IsBool  bool
 }
 
+func (a appFlag) AllNames() string {
+	names := []string{"--" + a.Name}
+	for _, alias := range a.Aliases {
+		names = append(names, "-"+alias)
+	}
+	return strings.Join(names, ",")
+}
+
 // From stdlib
 
 func isZeroValue(f *flag.Flag, value string) bool {

ffmd.tmpl

@@ -10,7 +10,7 @@
 {{end}}
 
 ```{{range $flag := .Flags}}
-[--{{$flag.Name}}]{{if not $flag.IsBool}}=[value]{{end}}
+[{{$flag.AllNames}}]{{if not $flag.IsBool}}=[value]{{end}}
 {{- end}}
 ```
 {{- if .Usage}}
@@ -22,5 +22,5 @@
 {{- end -}}
 {{range $flag := .Flags}}
 
-**--{{$flag.Name}}**{{if not $flag.IsBool}}=""{{end}}: {{$flag.Usage}}{{if $flag.Default}} (default: `{{$flag.Default}}`){{end}}
+**{{$flag.AllNames}}**{{if not $flag.IsBool}}=""{{end}}: {{$flag.Usage}}{{if $flag.Default}} (default: `{{$flag.Default}}`){{end}}
 {{end}}