Add IsExplicit function to check for non-default.

The IsSet function returns true even if the value that's available comes
from the default. Rather than changing the behavior of IsSet, adding a
new IsExplicit function allows checking for non-default values without
breaking existing behavior. This is intended to address issue #276 among
other things.

viper.go

@@ -612,7 +612,7 @@ func GetViper() *Viper {
 func Get(key string) interface{} { return v.Get(key) }
 func (v *Viper) Get(key string) interface{} {
 	lcaseKey := strings.ToLower(key)
-	val := v.find(lcaseKey)
+	val := v.find(lcaseKey, true)
 	if val == nil {
 		return nil
 	}
@@ -887,7 +887,7 @@ func (v *Viper) BindEnv(input ...string) error {
 // flag, env, config file, key/value store, default.
 // Viper will check to see if an alias exists first.
 // Note: this assumes a lower-cased key given.
-func (v *Viper) find(lcaseKey string) interface{} {
+func (v *Viper) find(lcaseKey string, useDefault bool) interface{} {
 
 	var (
 		val    interface{}
@@ -975,6 +975,11 @@ func (v *Viper) find(lcaseKey string) interface{} {
 		return nil
 	}
 
+	// Only use default values if asked
+	if !useDefault {
+		return nil
+	}
+
 	// Default next
 	val = v.searchMap(v.defaults, path)
 	if val != nil {
@@ -1020,7 +1025,16 @@ func readAsCSV(val string) ([]string, error) {
 func IsSet(key string) bool { return v.IsSet(key) }
 func (v *Viper) IsSet(key string) bool {
 	lcaseKey := strings.ToLower(key)
-	val := v.find(lcaseKey)
+	val := v.find(lcaseKey, true)
+	return val != nil
+}
+
+// IsExplicit checks to see if the key has a non-default value set.
+// IsExplicit is case-insensitive for a key.
+func IsExplicit(key string) bool { return v.IsExplicit(key) }
+func (v *Viper) IsExplicit(key string) bool {
+	lcaseKey := strings.ToLower(key)
+	val := v.find(lcaseKey, false)
 	return val != nil
 }
 

viper_test.go

@@ -766,6 +766,21 @@ func TestIsSet(t *testing.T) {
 	assert.False(t, v.IsSet("helloworld"))
 	v.Set("helloworld", "fubar")
 	assert.True(t, v.IsSet("helloworld"))
+	v.SetDefault("default", "value")
+	assert.True(t, v.IsSet("default"))
+}
+
+func TestIsExplicit(t *testing.T) {
+	v := New()
+	v.SetConfigType("yaml")
+	v.ReadConfig(bytes.NewBuffer(yamlExample))
+	assert.True(t, v.IsExplicit("clothing.jacket"))
+	assert.False(t, v.IsExplicit("clothing.jackets"))
+	assert.False(t, v.IsExplicit("helloworld"))
+	v.Set("helloworld", "fubar")
+	assert.True(t, v.IsExplicit("helloworld"))
+	v.SetDefault("default", "value")
+	assert.False(t, v.IsExplicit("default"))
 }
 
 func TestDirsSearch(t *testing.T) {