Add StringMap flag

StringMap wraps a `map[string]string` and parses inputs in the form of
"key=value".

app_test.go

@@ -432,6 +432,34 @@ func ExampleApp_Run_sliceValues() {
 	// error: <nil>
 }
 
+func ExampleApp_Run_mapValues() {
+	// set args for examples sake
+	os.Args = []string{
+		"multi_values",
+		"--stringMap", "parsed1=parsed two", "--stringMap", "parsed3=",
+	}
+	app := NewApp()
+	app.Name = "multi_values"
+	app.Flags = []Flag{
+		&StringMapFlag{Name: "stringMap"},
+	}
+	app.Action = func(ctx *Context) error {
+		for i, v := range ctx.FlagNames() {
+			fmt.Printf("%d-%s %#v\n", i, v, ctx.StringMap(v))
+		}
+		fmt.Printf("notfound %#v\n", ctx.StringMap("notfound"))
+		err := ctx.Err()
+		fmt.Println("error:", err)
+		return err
+	}
+
+	_ = app.Run(os.Args)
+	// Output:
+	// 0-stringMap map[string]string{"parsed1":"parsed two", "parsed3":""}
+	// notfound map[string]string(nil)
+	// error: <nil>
+}
+
 func TestApp_Run(t *testing.T) {
 	s := ""
 
@@ -2874,6 +2902,16 @@ func TestFlagAction(t *testing.T) {
 					return nil
 				},
 			},
+			&StringMapFlag{
+				Name: "f_string_map",
+				Action: func(c *Context, v map[string]string) error {
+					if _, ok := v["err"]; ok {
+						return fmt.Errorf("error string map")
+					}
+					c.App.Writer.Write([]byte(fmt.Sprintf("%v", v)))
+					return nil
+				},
+			},
 		},
 		Action: func(ctx *Context) error { return nil },
 	}
@@ -3034,6 +3072,16 @@ func TestFlagAction(t *testing.T) {
 			args: []string{"app", "--f_string=app", "--f_uint=1", "--f_int_slice=1,2,3", "--f_duration=1h30m20s", "c1", "--f_string=c1", "sub1", "--f_string=sub1"},
 			exp:  "app 1h30m20s [1 2 3] 1 c1 sub1 ",
 		},
+		{
+			name: "flag_string_map",
+			args: []string{"app", "--f_string_map=s1=s2,s3="},
+			exp:  "map[s1:s2 s3:]",
+		},
+		{
+			name: "flag_string_map_error",
+			args: []string{"app", "--f_string_map=err="},
+			err:  fmt.Errorf("error string map"),
+		},
 	}
 
 	for _, test := range tests {

flag.go

@@ -16,8 +16,9 @@ import (
 const defaultPlaceholder = "value"
 
 var (
-	defaultSliceFlagSeparator = ","
-	disableSliceFlagSeparator = false
+	defaultSliceFlagSeparator       = ","
+	defaultMapFlagKeyValueSeparator = "="
+	disableSliceFlagSeparator       = false
 )
 
 var (

flag_impl.go

@@ -192,7 +192,8 @@ func (f *FlagBase[T, C, V]) RunAction(ctx *Context) error {
 // IsSliceFlag returns true if the value type T is of kind slice
 func (f *FlagBase[T, C, VC]) IsSliceFlag() bool {
 	// TBD how to specify
-	return reflect.TypeOf(f.Value).Kind() == reflect.Slice
+	kind := reflect.TypeOf(f.Value).Kind()
+	return kind == reflect.Slice || kind == reflect.Map
 }
 
 // IsPersistent returns true if flag needs to be persistent across subcommands

flag_map_impl.go

@@ -0,0 +1,116 @@
+package cli
+
+import (
+	"encoding/json"
+	"fmt"
+	"reflect"
+	"sort"
+	"strings"
+)
+
+// MapBase wraps map[string]T to satisfy flag.Value
+type MapBase[T any, C any, VC ValueCreator[T, C]] struct {
+	dict       *map[string]T
+	hasBeenSet bool
+	value      Value
+}
+
+func (i MapBase[T, C, VC]) Create(val map[string]T, p *map[string]T, c C) Value {
+	*p = map[string]T{}
+	for k, v := range val {
+		(*p)[k] = v
+	}
+	var t T
+	np := new(T)
+	var vc VC
+	return &MapBase[T, C, VC]{
+		dict:  p,
+		value: vc.Create(t, np, c),
+	}
+}
+
+// NewMapBase makes a *MapBase with default values
+func NewMapBase[T any, C any, VC ValueCreator[T, C]](defaults map[string]T) *MapBase[T, C, VC] {
+	return &MapBase[T, C, VC]{
+		dict: &defaults,
+	}
+}
+
+// Set parses the value and appends it to the list of values
+func (i *MapBase[T, C, VC]) Set(value string) error {
+	if !i.hasBeenSet {
+		*i.dict = map[string]T{}
+		i.hasBeenSet = true
+	}
+
+	if strings.HasPrefix(value, slPfx) {
+		// Deserializing assumes overwrite
+		_ = json.Unmarshal([]byte(strings.Replace(value, slPfx, "", 1)), &i.dict)
+		i.hasBeenSet = true
+		return nil
+	}
+
+	for _, item := range flagSplitMultiValues(value) {
+		key, value, ok := strings.Cut(item, defaultMapFlagKeyValueSeparator)
+		if !ok {
+			return fmt.Errorf("item %q is missing separator %q", item, defaultMapFlagKeyValueSeparator)
+		}
+		if err := i.value.Set(strings.TrimSpace(value)); err != nil {
+			return err
+		}
+		tmp, ok := i.value.Get().(T)
+		if !ok {
+			return fmt.Errorf("unable to cast %v", i.value)
+		}
+		(*i.dict)[key] = tmp
+	}
+
+	return nil
+}
+
+// String returns a readable representation of this value (for usage defaults)
+func (i *MapBase[T, C, VC]) String() string {
+	v := i.Value()
+	var t T
+	if reflect.TypeOf(t).Kind() == reflect.String {
+		return fmt.Sprintf("%v", v)
+	}
+	return fmt.Sprintf("%T{%s}", v, i.ToString(v))
+}
+
+// Serialize allows MapBase to fulfill Serializer
+func (i *MapBase[T, C, VC]) Serialize() string {
+	jsonBytes, _ := json.Marshal(i.dict)
+	return fmt.Sprintf("%s%s", slPfx, string(jsonBytes))
+}
+
+// Value returns the mapping of values set by this flag
+func (i *MapBase[T, C, VC]) Value() map[string]T {
+	if i.dict == nil {
+		return map[string]T{}
+	}
+	return *i.dict
+}
+
+// Get returns the mapping of values set by this flag
+func (i *MapBase[T, C, VC]) Get() interface{} {
+	return *i.dict
+}
+
+func (i MapBase[T, C, VC]) ToString(t map[string]T) string {
+	var defaultVals []string
+	var vc VC
+	for _, k := range sortedKeys(t) {
+		defaultVals = append(defaultVals, k+defaultMapFlagKeyValueSeparator+vc.ToString(t[k]))
+	}
+	return strings.Join(defaultVals, ", ")
+}
+
+func sortedKeys[T any](dict map[string]T) []string {
+	keys := make([]string, 0, len(dict))
+	for k := range dict {
+		keys = append(keys, k)
+	}
+	sort.Strings(keys)
+	return keys
+}

flag_string_map.go

@@ -0,0 +1,27 @@
+package cli
+
+import "flag"
+
+type StringMap = MapBase[string, NoConfig, stringValue]
+type StringMapFlag = FlagBase[map[string]string, NoConfig, StringMap]
+
+var NewStringMap = NewMapBase[string, NoConfig, stringValue]
+
+// StringMap looks up the value of a local StringMapFlag, returns
+// nil if not found
+func (cCtx *Context) StringMap(name string) map[string]string {
+	if fs := cCtx.lookupFlagSet(name); fs != nil {
+		return lookupStringMap(name, fs)
+	}
+	return nil
+}
+
+func lookupStringMap(name string, set *flag.FlagSet) map[string]string {
+	f := set.Lookup(name)
+	if f != nil {
+		if mapping, ok := f.Value.(*StringMap); ok {
+			return mapping.Value()
+		}
+	}
+	return nil
+}