Merge pull request #2043 from jokemanfire/dev2

while print flag , the placeholder if need but not set.

examples_test.go

@@ -143,7 +143,7 @@ func ExampleCommand_Run_appHelp() {
 	//    help, h        Shows a list of commands or help for one command
 	//
 	// GLOBAL OPTIONS:
-	//    --name value   a name to say (default: "bob")
+	//    --name string  a name to say (default: "bob")
 	//    --help, -h     show help
 	//    --version, -v  print the version
 }

flag.go

@@ -142,6 +142,8 @@ type DocGenerationFlag interface {
 	// IsDefaultVisible returns whether the default value should be shown in
 	// help text
 	IsDefaultVisible() bool
+	// TypeName to detect if a flag is a string, bool, etc.
+	TypeName() string
 }
 
 // DocGenerationMultiValueFlag extends DocGenerationFlag for slice/map based flags.
@@ -304,9 +306,14 @@ func stringifyFlag(f Flag) string {
 	}
 	placeholder, usage := unquoteUsage(df.GetUsage())
 	needsPlaceholder := df.TakesValue()
-
+	// if needsPlaceholder is true, placeholder is empty
 	if needsPlaceholder && placeholder == "" {
-		placeholder = defaultPlaceholder
+		// try to get type from flag
+		if tname := df.TypeName(); tname != "" {
+			placeholder = tname
+		} else {
+			placeholder = defaultPlaceholder
+		}
 	}
 
 	defaultValueString := ""

flag_impl.go

@@ -5,6 +5,7 @@ import (
 	"flag"
 	"fmt"
 	"reflect"
+	"strings"
 )
 
 // Value represents a value as used by cli.
@@ -98,6 +99,42 @@ func (f *FlagBase[T, C, V]) GetValue() string {
 	return fmt.Sprintf("%v", f.Value)
 }
 
+// TypeName returns the type of the flag.
+func (f *FlagBase[T, C, V]) TypeName() string {
+	ty := reflect.TypeOf(f.Value)
+	if ty == nil {
+		return ""
+	}
+	// convert the typename to generic type
+	convertToGenericType := func(name string) string {
+		prefixMap := map[string]string{
+			"float": "float",
+			"int":   "int",
+			"uint":  "uint",
+		}
+		for prefix, genericType := range prefixMap {
+			if strings.HasPrefix(name, prefix) {
+				return genericType
+			}
+		}
+		return strings.ToLower(name)
+	}
+
+	switch ty.Kind() {
+	// if it is a Slice, then return the slice's inner type. Will nested slices be used in the future?
+	case reflect.Slice:
+		elemType := ty.Elem()
+		return convertToGenericType(elemType.Name())
+	// if it is a Map, then return the map's key and value types.
+	case reflect.Map:
+		keyType := ty.Key()
+		valueType := ty.Elem()
+		return fmt.Sprintf("%s=%s", convertToGenericType(keyType.Name()), convertToGenericType(valueType.Name()))
+	default:
+		return convertToGenericType(ty.Name())
+	}
+}
+
 // Apply populates the flag given the flag set and environment
 func (f *FlagBase[T, C, V]) Apply(set *flag.FlagSet) error {
 	tracef("apply (flag=%[1]q)", f.Name)