add support to tag validateFn (#1363)

## Fixes Or Enhances

This Pull Requests adds a new tag called `isvalid`

If the field is marked with the validator tag `isvalid`, the type must
implement the interface `Validate() error` and the return must be nil to
be considered `valid`

A possible use case is: when dealing with Enumerations, the type can
support a method `Validate() error` to check if the value is in specific
the range defined. If we use
[enumer](https://github.com/dmarkham/enumer) it generates a `IsA<Type>()
bool` method that can be used to verify if the enumeration is valid or
not, instead force the `oneof` tag (that needs to be always updated when
we add one new value.

I wrote a pull request to add a Validate method on enumerations
[here](dmarkham/enumer#102) and the interface
`Validate() error` seems pretty common.

It may clash with existing tags that people may register, this is
something that I don't know how to solve.

**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.

@go-playground/validator-maintainers

---------

Co-authored-by: nodivbyzero <[email protected]>

Author: peczenyj

README.md

@@ -262,6 +262,8 @@ validate := validator.New(validator.WithRequiredStructEnabled())
 | excluded_without | Excluded Without |
 | excluded_without_all | Excluded Without All |
 | unique | Unique |
+| validateFn | Verify if the method `Validate() error` does not return an error (or any specified method) |
+
 
 #### Aliases:
 | Tag | Description |

_examples/validate_fn/enum_enumer.go

@@ -0,0 +1,18 @@
+module github.com/peczenyj/validator/_examples/validate_fn
+
+go 1.20
+
+replace github.com/go-playground/validator/v10 => ../../../validator
+
+require github.com/go-playground/validator/v10 v10.26.0
+
+require (
+	github.com/gabriel-vasile/mimetype v1.4.8 // indirect
+	github.com/go-playground/locales v0.14.1 // indirect
+	github.com/go-playground/universal-translator v0.18.1 // indirect
+	github.com/leodido/go-urn v1.4.0 // indirect
+	golang.org/x/crypto v0.33.0 // indirect
+	golang.org/x/net v0.34.0 // indirect
+	golang.org/x/sys v0.30.0 // indirect
+	golang.org/x/text v0.22.0 // indirect
+)

_examples/validate_fn/go.mod

@@ -0,0 +1,21 @@
+github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
+github.com/gabriel-vasile/mimetype v1.4.8 h1:FfZ3gj38NjllZIeJAmMhr+qKL8Wu+nOoI3GqacKw1NM=
+github.com/gabriel-vasile/mimetype v1.4.8/go.mod h1:ByKUIKGjh1ODkGM1asKUbQZOLGrPjydw3hYPU2YU9t8=
+github.com/go-playground/assert/v2 v2.2.0 h1:JvknZsQTYeFEAhQwI4qEt9cyV5ONwRHC+lYKSsYSR8s=
+github.com/go-playground/locales v0.14.1 h1:EWaQ/wswjilfKLTECiXz7Rh+3BjFhfDFKv/oXslEjJA=
+github.com/go-playground/locales v0.14.1/go.mod h1:hxrqLVvrK65+Rwrd5Fc6F2O76J/NuW9t0sjnWqG1slY=
+github.com/go-playground/universal-translator v0.18.1 h1:Bcnm0ZwsGyWbCzImXv+pAJnYK9S473LQFuzCbDbfSFY=
+github.com/go-playground/universal-translator v0.18.1/go.mod h1:xekY+UJKNuX9WP91TpwSH2VMlDf28Uj24BCp08ZFTUY=
+github.com/leodido/go-urn v1.4.0 h1:WT9HwE9SGECu3lg4d/dIA+jxlljEa1/ffXKmRjqdmIQ=
+github.com/leodido/go-urn v1.4.0/go.mod h1:bvxc+MVxLKB4z00jd1z+Dvzr47oO32F/QSNjSBOlFxI=
+github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
+github.com/stretchr/testify v1.8.4 h1:CcVxjf3Q8PM0mHUKJCdn+eZZtm5yQwehR5yeSVQQcUk=
+golang.org/x/crypto v0.33.0 h1:IOBPskki6Lysi0lo9qQvbxiQ+FvsCC/YWOecCHAixus=
+golang.org/x/crypto v0.33.0/go.mod h1:bVdXmD7IV/4GdElGPozy6U7lWdRXA4qyRVGJV57uQ5M=
+golang.org/x/net v0.34.0 h1:Mb7Mrk043xzHgnRM88suvJFwzVrRfHEHJEl5/71CKw0=
+golang.org/x/net v0.34.0/go.mod h1:di0qlW3YNM5oh6GqDGQr92MyTozJPmybPK4Ev/Gm31k=
+golang.org/x/sys v0.30.0 h1:QjkSwP/36a20jFYWkSue1YwXzLmsV5Gfq7Eiy72C1uc=
+golang.org/x/sys v0.30.0/go.mod h1:/VUhepiaJMQUp4+oa/7Zr1D23ma6VTLIYjOOTFZPUcA=
+golang.org/x/text v0.22.0 h1:bofq7m3/HAFvbF51jz3Q9wLg3jkvSPuiZu/pD1XwgtM=
+golang.org/x/text v0.22.0/go.mod h1:YRoo4H8PVmsu+E3Ou7cqLVH8oXWIHVoX0jqUWALQhfY=
+gopkg.in/yaml.v3 v3.0.1 h1:fxVm/GzAzEWqLHuvctI91KS9hhNmmWOoWu0XTYJS7CA=

_examples/validate_fn/go.sum

@@ -0,0 +1,52 @@
+package main
+
+import (
+	"errors"
+	"fmt"
+
+	"github.com/go-playground/validator/v10"
+)
+
+//go:generate enumer -type=Enum
+type Enum uint8
+
+const (
+	Zero Enum = iota
+	One
+	Two
+	Three
+)
+
+func (e *Enum) Validate() error {
+	if e == nil {
+		return errors.New("can't be nil")
+	}
+
+	return nil
+}
+
+type Struct struct {
+	Foo *Enum `validate:"validateFn"`         // uses Validate() error by default
+	Bar Enum  `validate:"validateFn=IsAEnum"` // uses IsAEnum() bool provided by enumer
+}
+
+func main() {
+	validate := validator.New()
+
+	var x Struct
+
+	x.Bar = Enum(64)
+
+	if err := validate.Struct(x); err != nil {
+		fmt.Printf("Expected Err(s):\n%+v\n", err)
+	}
+
+	x = Struct{
+		Foo: new(Enum),
+		Bar: One,
+	}
+
+	if err := validate.Struct(x); err != nil {
+		fmt.Printf("Unexpected Err(s):\n%+v\n", err)
+	}
+}

_examples/validate_fn/main.go

@@ -2,10 +2,12 @@ package validator
 
 import (
 	"bytes"
+	"cmp"
 	"context"
 	"crypto/sha256"
 	"encoding/hex"
 	"encoding/json"
+	"errors"
 	"fmt"
 	"io/fs"
 	"net"
@@ -244,6 +246,7 @@ var (
 		"cron":                          isCron,
 		"spicedb":                       isSpiceDB,
 		"ein":                           isEIN,
+		"validateFn":                    isValidateFn,
 	}
 )
 
@@ -3046,3 +3049,60 @@ func isEIN(fl FieldLevel) bool {
 
 	return einRegex().MatchString(field.String())
 }
+
+func isValidateFn(fl FieldLevel) bool {
+	const defaultParam = `Validate`
+
+	field := fl.Field()
+	validateFn := cmp.Or(fl.Param(), defaultParam)
+
+	ok, err := tryCallValidateFn(field, validateFn)
+	if err != nil {
+		return false
+	}
+
+	return ok
+}
+
+var (
+	errMethodNotFound          = errors.New(`method not found`)
+	errMethodReturnNoValues    = errors.New(`method return o values (void)`)
+	errMethodReturnInvalidType = errors.New(`method should return invalid type`)
+)
+
+func tryCallValidateFn(field reflect.Value, validateFn string) (bool, error) {
+	method := field.MethodByName(validateFn)
+	if field.CanAddr() && !method.IsValid() {
+		method = field.Addr().MethodByName(validateFn)
+	}
+
+	if !method.IsValid() {
+		return false, fmt.Errorf("unable to call %q on type %q: %w",
+			validateFn, field.Type().String(), errMethodNotFound)
+	}
+
+	returnValues := method.Call([]reflect.Value{})
+	if len(returnValues) == 0 {
+		return false, fmt.Errorf("unable to use result of method %q on type %q: %w",
+			validateFn, field.Type().String(), errMethodReturnNoValues)
+	}
+
+	firstReturnValue := returnValues[0]
+
+	switch firstReturnValue.Kind() {
+	case reflect.Bool:
+		return firstReturnValue.Bool(), nil
+	case reflect.Interface:
+		errorType := reflect.TypeOf((*error)(nil)).Elem()
+
+		if firstReturnValue.Type().Implements(errorType) {
+			return firstReturnValue.IsNil(), nil
+		}
+
+		return false, fmt.Errorf("unable to use result of method %q on type %q: %w (got interface %v expect error)",
+			validateFn, field.Type().String(), errMethodReturnInvalidType, firstReturnValue.Type().String())
+	default:
+		return false, fmt.Errorf("unable to use result of method %q on type %q: %w (got %v expect error or bool)",
+			validateFn, field.Type().String(), errMethodReturnInvalidType, firstReturnValue.Type().String())
+	}
+}

baked_in.go

@@ -3,6 +3,7 @@ package validator
 import (
 	"bytes"
 	sql "database/sql/driver"
+	"errors"
 	"testing"
 	"time"
 )
@@ -1097,3 +1098,39 @@ func BenchmarkOneofParallel(b *testing.B) {
 		}
 	})
 }
+
+type T struct{}
+
+func (*T) Validate() error { return errors.New("ops") }
+
+func BenchmarkValidateFnSequencial(b *testing.B) {
+	validate := New()
+
+	type Test struct {
+		T T `validate:"validateFn"`
+	}
+
+	test := &Test{}
+
+	b.ResetTimer()
+	for n := 0; n < b.N; n++ {
+		_ = validate.Struct(test)
+	}
+}
+
+func BenchmarkValidateFnParallel(b *testing.B) {
+	validate := New()
+
+	type Test struct {
+		T T `validate:"validateFn"`
+	}
+
+	test := &Test{}
+
+	b.ResetTimer()
+	b.RunParallel(func(pb *testing.PB) {
+		for pb.Next() {
+			_ = validate.Struct(test)
+		}
+	})
+}

benchmarks_test.go

@@ -756,6 +756,20 @@ in a field of the struct specified via a parameter.
 	// For slices of struct:
 	Usage: unique=field
 
+# ValidateFn
+
+This validates that an object responds to a method that can return error or bool.
+By default it expects an interface `Validate() error` and check that the method
+does not return an error. Other methods can be specified using two signatures:
+If the method returns an error, it check if the return value is nil.
+If the method returns a boolean, it checks if the value is true.
+
+	// to use the default method Validate() error
+	Usage: validateFn
+
+	// to use the custom method IsValid() bool (or error)
+	Usage: validateFn=IsValid
+
 # Alpha Only
 
 This validates that a string value contains ASCII alpha characters only

doc.go

@@ -1484,6 +1484,11 @@ func RegisterDefaultTranslations(v *validator.Validate, trans ut.Translator) (er
 			translation: "{0} must be a valid cve identifier",
 			override:    false,
 		},
+		{
+			tag:         "validateFn",
+			translation: "{0} must be a valid object",
+			override:    false,
+		},
 	}
 
 	for _, t := range translations {

translations/en/en.go

@@ -10,6 +10,10 @@ import (
 	"github.com/go-playground/validator/v10"
 )
 
+type Foo struct{}
+
+func (Foo) IsBar() bool { return false }
+
 func TestTranslations(t *testing.T) {
 	eng := english.New()
 	uni := ut.New(eng, eng)
@@ -181,6 +185,7 @@ func TestTranslations(t *testing.T) {
 		CveString          string        `validate:"cve"`
 		MinDuration        time.Duration `validate:"min=1h30m,max=2h"`
 		MaxDuration        time.Duration `validate:"min=1h30m,max=2h"`
+		ValidateFn         Foo           `validate:"validateFn=IsBar"`
 	}
 
 	var test Test
@@ -805,6 +810,10 @@ func TestTranslations(t *testing.T) {
 			ns:       "Test.MaxDuration",
 			expected: "MaxDuration must be 2h or less",
 		},
+		{
+			ns:       "Test.ValidateFn",
+			expected: "ValidateFn must be a valid object",
+		},
 	}
 
 	for _, tt := range tests {