fix: support StringMap values from map value sources (#1634)

value_source.go

@@ -3,6 +3,7 @@ package cli
 import (
 	"fmt"
 	"os"
+	"reflect"
 	"strings"
 )
 
@@ -253,6 +254,22 @@ func (mvs *mapValueSource) Lookup() (string, bool) {
 	if v, ok := mvs.ms.Lookup(mvs.key); !ok {
 		return "", false
 	} else {
-		return fmt.Sprintf("%+v", v), true
+		return mapValueSourceString(v), true
 	}
 }
+
+// mapValueSourceString converts a looked-up value to the string form
+// consumed by flag values. Map values are serialized through the same
+// path as StringMap Serialize so they round-trip via MapBase.Set,
+// while scalars and slices keep their historical formatting.
+func mapValueSourceString(v any) string {
+	if val := reflect.ValueOf(v); val.IsValid() && val.Kind() == reflect.Map {
+		stringMap := make(map[string]string, val.Len())
+		iter := val.MapRange()
+		for iter.Next() {
+			stringMap[fmt.Sprintf("%v", iter.Key().Interface())] = fmt.Sprintf("%v", iter.Value().Interface())
+		}
+		return NewStringMap(stringMap).Serialize()
+	}
+	return fmt.Sprintf("%+v", v)
+}

value_source_test.go

@@ -1,6 +1,7 @@
 package cli
 
 import (
+	"context"
 	"fmt"
 	"math/rand"
 	"os"
@@ -335,6 +336,87 @@ func TestMapValueSource(t *testing.T) {
 	}
 }
 
+func TestMapValueSourceStringMap(t *testing.T) {
+	// Regression test for https://github.com/urfave/cli/issues/1634:
+	// map-sourced values must round-trip through StringMap parsing
+	// instead of Go-syntax "%+v" which MapBase.Set rejects.
+	tests := []struct {
+		name  string
+		m     map[any]any
+		key   string
+		want  map[string]string
+		found bool
+	}{
+		{
+			name: "map any any",
+			m: map[any]any{
+				"labels": map[any]any{"env": "prod", "team": "platform"},
+			},
+			key:   "labels",
+			want:  map[string]string{"env": "prod", "team": "platform"},
+			found: true,
+		},
+		{
+			name: "map string any",
+			m: map[any]any{
+				"labels": map[string]any{"env": "prod", "team": "platform"},
+			},
+			key:   "labels",
+			want:  map[string]string{"env": "prod", "team": "platform"},
+			found: true,
+		},
+		{
+			name: "map string string",
+			m: map[any]any{
+				"labels": map[string]string{"env": "prod", "team": "platform"},
+			},
+			key:   "labels",
+			want:  map[string]string{"env": "prod", "team": "platform"},
+			found: true,
+		},
+		{
+			name: "missing key",
+			m: map[any]any{
+				"labels": map[any]any{"env": "prod"},
+			},
+			key:   "other",
+			found: false,
+		},
+	}
+
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			ms := NewMapSource("test", test.m)
+			m := NewMapValueSource(test.key, ms)
+			val, ok := m.Lookup()
+			if !test.found {
+				assert.False(t, ok)
+				return
+			}
+			require.True(t, ok)
+			sm := NewStringMap(nil)
+			require.NoError(t, sm.Set(val))
+			assert.Equal(t, test.want, sm.Value())
+		})
+	}
+}
+
+func TestStringMapFlagFromMapSource(t *testing.T) {
+	ms := NewMapSource("test", map[any]any{
+		"labels": map[any]any{"env": "prod", "team": "platform"},
+	})
+	cmd := &Command{
+		Flags: []Flag{
+			&StringMapFlag{Name: "labels", Sources: NewValueSourceChain(NewMapValueSource("labels", ms))},
+		},
+		Action: func(_ context.Context, cmd *Command) error {
+			assert.Equal(t, map[string]string{"env": "prod", "team": "platform"}, cmd.StringMap("labels"))
+			return nil
+		},
+	}
+	require.NoError(t, cmd.Run(buildTestContext(t), []string{"app"}))
+}
+
 func TestMapValueSourceStringer(t *testing.T) {
 	m := map[any]any{
 		"foo": map[any]any{