fix isPathShadowedInFlatMap type cast bug (#1585)

* fix isPathShadowedInFlatMap type cast bug

* Add "IsPathShadowedInFlatMap" method unit test

* fix: typo

* add an unit test for flag shadow

---------

Co-authored-by: Márk Sági-Kazár <sagikazarmark@users.noreply.github.com>

viper.go

@@ -827,10 +827,12 @@ func (v *Viper) isPathShadowedInDeepMap(path []string, m map[string]any) string
 //	"foo.bar.baz" in a lower-priority map
 func (v *Viper) isPathShadowedInFlatMap(path []string, mi any) string {
 	// unify input map
-	var m map[string]any
-	switch mi.(type) {
-	case map[string]string, map[string]FlagValue:
-		m = cast.ToStringMap(mi)
+	var m map[string]interface{}
+	switch miv := mi.(type) {
+	case map[string]string:
+		m = castMapStringToMapInterface(miv)
+	case map[string]FlagValue:
+		m = castMapFlagToMapInterface(miv)
 	default:
 		return ""
 	}

viper_test.go

@@ -2575,6 +2575,51 @@ func TestSliceIndexAccess(t *testing.T) {
 	assert.Equal(t, "Static", v.GetString("tv.0.episodes.1.2"))
 }
 
+func TestIsPathShadowedInFlatMap(t *testing.T) {
+	v := New()
+
+	stringMap := map[string]string{
+		"foo": "value",
+	}
+
+	flagMap := map[string]FlagValue{
+		"foo": pflagValue{},
+	}
+
+	path1 := []string{"foo", "bar"}
+	expected1 := "foo"
+
+	// "foo.bar" should shadowed by "foo"
+	assert.Equal(t, expected1, v.isPathShadowedInFlatMap(path1, stringMap))
+	assert.Equal(t, expected1, v.isPathShadowedInFlatMap(path1, flagMap))
+
+	path2 := []string{"bar", "foo"}
+	expected2 := ""
+
+	// "bar.foo" should not shadowed by "foo"
+	assert.Equal(t, expected2, v.isPathShadowedInFlatMap(path2, stringMap))
+	assert.Equal(t, expected2, v.isPathShadowedInFlatMap(path2, flagMap))
+}
+
+func TestFlagShadow(t *testing.T) {
+	v := New()
+
+	v.SetDefault("foo.bar1.bar2", "default")
+
+	flags := pflag.NewFlagSet("test", pflag.ContinueOnError)
+	flags.String("foo.bar1", "shadowed", "")
+	flags.VisitAll(func(flag *pflag.Flag) {
+		flag.Changed = true
+	})
+
+	v.BindPFlags(flags)
+
+	assert.Equal(t, "shadowed", v.GetString("foo.bar1"))
+	// the default "foo.bar1.bar2" value should shadowed by flag "foo.bar1" value
+	// and should return an empty string
+	assert.Equal(t, "", v.GetString("foo.bar1.bar2"))
+}
+
 func BenchmarkGetBool(b *testing.B) {
 	key := "BenchmarkGetBool"
 	v = New()