Fixed missing keys from returned errors in map validation

[angelo1121]

Fixes Or Enhances

Bug Description:

The ValidateMapCtx function calls the VarCtx(ctx context.Context, field interface{}, tag string) (err error) method, but the returned errors do not contain keys.

package main

import (
	"fmt"

	"github.com/go-playground/validator/v10"
)

func main() {
	validate := validator.New()

	data := map[string]interface{}{"email": "emailaddress"}
	rules := map[string]interface{}{"email": "required,email"}
	errs := validate.ValidateMap(data, rules) // when VarCtx is called
	fmt.Println(errs)
	//output: map[email:Key: '' Error:Field validation for '' failed on the 'email' tag]
}

Fix:

Added a new method VarWithKeyCtx(ctx context.Context, key string, field interface{}, tag string) (err error) to support validating a single variable, ensuring that the returned error contains the key of the field. This retains compatibility with the current VarCtx(...) method. Now, ValidateMapCtx will call the new VarWithKeyCtx(...) method.

package main

import (
	"fmt"

	"github.com/go-playground/validator/v10"
)

func main() {
	validate := validator.New()

	data := map[string]interface{}{"email": "emailaddress"}
	rules := map[string]interface{}{"email": "required,email"}
	errs := validate.ValidateMap(data, rules) // when the new VarWithKeyCtx is called
	fmt.Println(errs)
	//output: map[email:Key: 'email' Error:Field validation for 'email' failed on the 'email' tag]
}

Make sure that you've checked the boxes below before you submit PR:

• Tests exist or have been written that cover this particular change.

@go-playground/validator-maintainers

[coveralls]

coverage: 74.319% (+0.03%) from 74.291%
when pulling 1152639 on angelo1121:fix-map-validation-missing-keys
into a947377 on go-playground:master.