fix slice usage with env variables

viper.go

@@ -28,6 +28,7 @@ import (
 	"os"
 	"path/filepath"
 	"reflect"
+	"slices"
 	"strconv"
 	"strings"
 	"sync"
@@ -692,52 +693,85 @@ func (v *Viper) searchMap(source map[string]any, path []string) any {
 // searchMapWithAliases recursively searches for slice field in source map and
 // replace them with the environment variable value if it exists.
 //
-// Returns replaced values.
-func (v *Viper) searchAndReplaceSliceValueWithEnv(source any, envKey string) any {
+// Returns replaced values, and a boolean if the value was found in
+// environment varaible.
+func (v *Viper) searchAndReplaceSliceValueWithEnv(source any, envKey string) (any, bool) {
+
 	switch sourceValue := source.(type) {
 	case []any:
 		var newSliceValues []any
-		for i, sliceValue := range sourceValue {
+		if len(sourceValue) <= 0 {
+			return newSliceValues, false
+
+		}
+
+		var exists []bool
+		for i := 0; ; i++ {
 			envKey := envKey + v.keyDelim + strconv.Itoa(i)
-			switch existingValue := sliceValue.(type) {
+			var value any
+			var existDefault = true
+			if len(sourceValue) < i+1 {
+				value = sourceValue[0]
+				existDefault = false
+			} else {
+				value = sourceValue[i]
+			}
+			switch existingValue := value.(type) {
 			case map[string]any:
-				newVal := v.searchAndReplaceSliceValueWithEnv(existingValue, envKey)
+				newVal, found := v.searchAndReplaceSliceValueWithEnv(existingValue, envKey)
+				if !found && !existDefault {
+					return newSliceValues, slices.Contains(exists, true)
+				}
 				newSliceValues = append(newSliceValues, newVal)
+				exists = append(exists, found || existDefault)
 
 			default:
 				if newVal, ok := v.getEnv(v.mergeWithEnvPrefix(envKey)); ok {
 					newSliceValues = append(newSliceValues, newVal)
+					exists = append(exists, true)
 				} else {
-					newSliceValues = append(newSliceValues, existingValue)
+					exists = append(exists, false || existDefault)
+					if existDefault {
+						newSliceValues = append(newSliceValues, existingValue)
+					} else {
+						return newSliceValues, slices.Contains(exists, true)
+					}
 				}
 			}
 		}
-		return newSliceValues
+		return newSliceValues, slices.Contains(exists, true)
 
 	case map[string]any:
 		var newMapValues map[string]any = make(map[string]any)
+		var exists []bool
 		for key, mapValue := range sourceValue {
 			envKey := envKey + v.keyDelim + key
 			switch existingValue := mapValue.(type) {
 			case map[string]any:
-				newVal := v.searchAndReplaceSliceValueWithEnv(existingValue, envKey)
+				newVal, found := v.searchAndReplaceSliceValueWithEnv(existingValue, envKey)
+				if !found {
+					return newMapValues, false
+				}
 				newMapValues[key] = newVal
+				exists = append(exists, found)
 
 			default:
 				if newVal, ok := v.getEnv(v.mergeWithEnvPrefix(envKey)); ok {
 					newMapValues[key] = newVal
+					exists = append(exists, true)
 				} else {
+					exists = append(exists, false)
 					newMapValues[key] = existingValue
 				}
 			}
 		}
-		return newMapValues
+		return newMapValues, slices.Contains(exists, true)
 
 	default:
 		if newVal, ok := v.getEnv(v.mergeWithEnvPrefix(envKey)); ok {
-			return newVal
+			return newVal, true
 		} else {
-			return source
+			return source, false
 		}
 	}
 }
@@ -961,7 +995,7 @@ func (v *Viper) Get(key string) any {
 
 	// Check for Env override again, to handle slices
 	if v.automaticEnvApplied {
-		val = v.searchAndReplaceSliceValueWithEnv(val, lcaseKey)
+		val, _ = v.searchAndReplaceSliceValueWithEnv(val, lcaseKey)
 	}
 
 	if v.typeByDefValue {

viper_test.go

@@ -2668,6 +2668,7 @@ func TestSliceIndexAutomaticEnv(t *testing.T) {
 	t.Setenv("MODES_2", "300")
 	t.Setenv("CLIENTS_1_NAME", "baz")
 	t.Setenv("PROXY_CLIENTS_0_NAME", "ProxyFoo")
+	t.Setenv("PROXY_CLIENTS_3_NAME", "ProxyNew")
 
 	SetEnvKeyReplacer(strings.NewReplacer(".", "_"))
 	AutomaticEnv()
@@ -2683,6 +2684,7 @@ func TestSliceIndexAutomaticEnv(t *testing.T) {
 	assert.Equal(t, "foo", config.Clients[0].Name)
 	assert.Equal(t, "baz", config.Clients[1].Name)
 	assert.Equal(t, "ProxyFoo", config.Proxy.Clients[0].Name)
+	assert.Equal(t, "ProxyNew", config.Proxy.Clients[3].Name)
 }
 
 func TestIsPathShadowedInFlatMap(t *testing.T) {