rules.NewDefaultRules()

someRule := validator.Rule{
	Name: "SomeRule",
	RuleFunc: func(observers *validator.Events, addError validator.AddErrFunc) {
		addError(validator.Message("%s", "some error message"))
	},
}

someOtherRule := validator.Rule{
	Name: "SomeOtherRule",
	RuleFunc: func(observers *validator.Events, addError validator.AddErrFunc) {
		addError(validator.Message("%s", "some other error message"))
	},
}

validator.ValidateWithRules(s, q, rules.NewRules(someRule, someOtherRule))

someRules := rules.NewDefaultRules()
someRules.AddRule("SomeRule", someRule.RuleFunc)
someRules.RemoveRule("SomeRule")

package main

import (
	"github.com/vektah/gqlparser/v2/ast"
	"github.com/vektah/gqlparser/v2/gqlparser"
	"github.com/vektah/gqlparser/v2/validator/rules"
)

func main() {
	schema, _ := gqlparser.LoadSchema(&ast.Source{Name: "graph/schema.graphqls", Input: `
	type Query {
		bar: String!
	}
	`, BuiltIn: false})
	queryStr := `
		query Foo {
			bar
		}
	`

	// 1. Create the default rule set
	defaultRules := rules.NewDefaultRules()

	// 2. Customise rules if required
	// defaultRules.RemoveRule(rules.MaxIntrospectionDepth.Name)

	// 3. Parse and validate a query using the rule set
	queryDoc, errs := gqlparser.LoadQueryWithRules(schema, queryStr, defaultRules)
	if len(errs) != 0 {
		// Handle validation errors
	}
	_ = queryDoc
}