Feature: nested struct validation (#1122)

## Fixes #367, #906

**Make sure that you've checked the boxes below before you submit PR:**
- [x] Tests exist or have been written that cover this particular
change.

A test has been added for custom tags, however I was not brave enough to
actually update the tests for all required/excluded tag variants before
getting an initial feedback, but I'm willing to do so if this ever gets
any further.

Same goes for documentation.

The implementation supports both struct and struct pointer validations
for custom tags and all required/excluded tag variants.

Struct validity is evaluated first and fields are evaluated only if the
struct is valid, though I'm not sure if this is the desired behavior.

@go-playground/validator-maintainers

Author: MysteriousPotato

baked_in.go

@@ -1710,7 +1710,7 @@ func hasValue(fl FieldLevel) bool {
 		if fl.(*validate).fldIsPointer && field.Interface() != nil {
 			return true
 		}
-		return field.IsValid() && field.Interface() != reflect.Zero(field.Type()).Interface()
+		return field.IsValid() && !field.IsZero()
 	}
 }
 
@@ -1734,7 +1734,7 @@ func requireCheckFieldKind(fl FieldLevel, param string, defaultNotFoundValue boo
 		if nullable && field.Interface() != nil {
 			return false
 		}
-		return field.IsValid() && field.Interface() == reflect.Zero(field.Type()).Interface()
+		return field.IsValid() && field.IsZero()
 	}
 }
 

cache.go

@@ -20,6 +20,7 @@ const (
 	typeOr
 	typeKeys
 	typeEndKeys
+	typeNestedStructLevel
 )
 
 const (
@@ -152,7 +153,7 @@ func (v *Validate) extractStructCache(current reflect.Value, sName string) *cStr
 		// and so only struct level caching can be used instead of combined with Field tag caching
 
 		if len(tag) > 0 {
-			ctag, _ = v.parseFieldTagsRecursive(tag, fld.Name, "", false)
+			ctag, _ = v.parseFieldTagsRecursive(tag, fld, "", false)
 		} else {
 			// even if field doesn't have validations need cTag for traversing to potential inner/nested
 			// elements of the field.
@@ -171,7 +172,7 @@ func (v *Validate) extractStructCache(current reflect.Value, sName string) *cStr
 	return cs
 }
 
-func (v *Validate) parseFieldTagsRecursive(tag string, fieldName string, alias string, hasAlias bool) (firstCtag *cTag, current *cTag) {
+func (v *Validate) parseFieldTagsRecursive(tag string, field reflect.StructField, alias string, hasAlias bool) (firstCtag *cTag, current *cTag) {
 	var t string
 	noAlias := len(alias) == 0
 	tags := strings.Split(tag, tagSeparator)
@@ -185,9 +186,9 @@ func (v *Validate) parseFieldTagsRecursive(tag string, fieldName string, alias s
 		// check map for alias and process new tags, otherwise process as usual
 		if tagsVal, found := v.aliases[t]; found {
 			if i == 0 {
-				firstCtag, current = v.parseFieldTagsRecursive(tagsVal, fieldName, t, true)
+				firstCtag, current = v.parseFieldTagsRecursive(tagsVal, field, t, true)
 			} else {
-				next, curr := v.parseFieldTagsRecursive(tagsVal, fieldName, t, true)
+				next, curr := v.parseFieldTagsRecursive(tagsVal, field, t, true)
 				current.next, current = next, curr
 
 			}
@@ -235,7 +236,7 @@ func (v *Validate) parseFieldTagsRecursive(tag string, fieldName string, alias s
 				}
 			}
 
-			current.keys, _ = v.parseFieldTagsRecursive(string(b[:len(b)-1]), fieldName, "", false)
+			current.keys, _ = v.parseFieldTagsRecursive(string(b[:len(b)-1]), field, "", false)
 			continue
 
 		case endKeysTag:
@@ -284,14 +285,18 @@ func (v *Validate) parseFieldTagsRecursive(tag string, fieldName string, alias s
 
 				current.tag = vals[0]
 				if len(current.tag) == 0 {
-					panic(strings.TrimSpace(fmt.Sprintf(invalidValidation, fieldName)))
+					panic(strings.TrimSpace(fmt.Sprintf(invalidValidation, field.Name)))
 				}
 
 				if wrapper, ok := v.validations[current.tag]; ok {
 					current.fn = wrapper.fn
 					current.runValidationWhenNil = wrapper.runValidatinOnNil
 				} else {
-					panic(strings.TrimSpace(fmt.Sprintf(undefinedValidation, current.tag, fieldName)))
+					panic(strings.TrimSpace(fmt.Sprintf(undefinedValidation, current.tag, field.Name)))
+				}
+
+				if current.typeof == typeDefault && isNestedStructOrStructPtr(field) {
+					current.typeof = typeNestedStructLevel
 				}
 
 				if len(orVals) > 1 {
@@ -319,7 +324,7 @@ func (v *Validate) fetchCacheTag(tag string) *cTag {
 		// isn't parsed again.
 		ctag, found = v.tagCache.Get(tag)
 		if !found {
-			ctag, _ = v.parseFieldTagsRecursive(tag, "", "", false)
+			ctag, _ = v.parseFieldTagsRecursive(tag, reflect.StructField{}, "", false)
 			v.tagCache.Set(tag, ctag)
 		}
 	}

doc.go

@@ -247,7 +247,7 @@ Example #2
 This validates that the value is not the data types default zero value.
 For numbers ensures value is not zero. For strings ensures value is
 not "". For slices, maps, pointers, interfaces, channels and functions
-ensures the value is not nil.
+ensures the value is not nil. For structs ensures value is not the zero value.
 
 	Usage: required
 
@@ -256,7 +256,7 @@ ensures the value is not nil.
 The field under validation must be present and not empty only if all
 the other specified fields are equal to the value following the specified
 field. For strings ensures value is not "". For slices, maps, pointers,
-interfaces, channels and functions ensures the value is not nil.
+interfaces, channels and functions ensures the value is not nil. For structs ensures value is not the zero value.
 
 	Usage: required_if
 
@@ -273,7 +273,7 @@ Examples:
 The field under validation must be present and not empty unless all
 the other specified fields are equal to the value following the specified
 field. For strings ensures value is not "". For slices, maps, pointers,
-interfaces, channels and functions ensures the value is not nil.
+interfaces, channels and functions ensures the value is not nil. For structs ensures value is not the zero value.
 
 	Usage: required_unless
 
@@ -290,7 +290,7 @@ Examples:
 The field under validation must be present and not empty only if any
 of the other specified fields are present. For strings ensures value is
 not "". For slices, maps, pointers, interfaces, channels and functions
-ensures the value is not nil.
+ensures the value is not nil. For structs ensures value is not the zero value.
 
 	Usage: required_with
 
@@ -307,7 +307,7 @@ Examples:
 The field under validation must be present and not empty only if all
 of the other specified fields are present. For strings ensures value is
 not "". For slices, maps, pointers, interfaces, channels and functions
-ensures the value is not nil.
+ensures the value is not nil. For structs ensures value is not the zero value.
 
 	Usage: required_with_all
 
@@ -321,7 +321,7 @@ Example:
 The field under validation must be present and not empty only when any
 of the other specified fields are not present. For strings ensures value is
 not "". For slices, maps, pointers, interfaces, channels and functions
-ensures the value is not nil.
+ensures the value is not nil. For structs ensures value is not the zero value.
 
 	Usage: required_without
 
@@ -338,7 +338,7 @@ Examples:
 The field under validation must be present and not empty only when all
 of the other specified fields are not present. For strings ensures value is
 not "". For slices, maps, pointers, interfaces, channels and functions
-ensures the value is not nil.
+ensures the value is not nil. For structs ensures value is not the zero value.
 
 	Usage: required_without_all
 
@@ -352,7 +352,7 @@ Example:
 The field under validation must not be present or not empty only if all
 the other specified fields are equal to the value following the specified
 field. For strings ensures value is not "". For slices, maps, pointers,
-interfaces, channels and functions ensures the value is not nil.
+interfaces, channels and functions ensures the value is not nil. For structs ensures value is not the zero value.
 
 	Usage: excluded_if
 
@@ -369,7 +369,7 @@ Examples:
 The field under validation must not be present or empty unless all
 the other specified fields are equal to the value following the specified
 field. For strings ensures value is not "". For slices, maps, pointers,
-interfaces, channels and functions ensures the value is not nil.
+interfaces, channels and functions ensures the value is not nil. For structs ensures value is not the zero value.
 
 	Usage: excluded_unless
 

util.go

@@ -286,3 +286,11 @@ func panicIf(err error) {
 		panic(err.Error())
 	}
 }
+
+func isNestedStructOrStructPtr(v reflect.StructField) bool {
+	if v.Type == nil {
+		return false
+	}
+	kind := v.Type.Kind()
+	return kind == reflect.Struct || kind == reflect.Ptr && v.Type.Elem().Kind() == reflect.Struct
+}

validator.go

@@ -170,7 +170,7 @@ func (v *validate) traverseField(ctx context.Context, parent reflect.Value, curr
 
 				if ct.typeof == typeStructOnly {
 					goto CONTINUE
-				} else if ct.typeof == typeIsDefault {
+				} else if ct.typeof == typeIsDefault || ct.typeof == typeNestedStructLevel {
 					// set Field Level fields
 					v.slflParent = parent
 					v.flField = current