make graphql.Do() aware custom validation rule

add "ValidationRules" field to graphql.Params, to be able to customize
validation rules per query.

go.mod

@@ -1 +1,3 @@
 module github.com/graphql-go/graphql
+
+go 1.14

graphql.go

@@ -28,6 +28,12 @@ type Params struct {
 	// one operation.
 	OperationName string
 
+	// ValidationRules is for overriding rules of document validation.  Default
+	// SpecifiedRules are ignored when specified this option other than nil.
+	// So it would be better that combining your rules with SpecifiedRules to
+	// fill this.
+	ValidationRules []ValidationRuleFn
+
 	// Context may be provided to pass application-specific per-request
 	// information to resolve functions.
 	Context context.Context
@@ -84,7 +90,7 @@ func Do(p Params) *Result {
 	}
 
 	// validate document
-	validationResult := ValidateDocument(&p.Schema, AST, nil)
+	validationResult := ValidateDocument(&p.Schema, AST, p.ValidationRules)
 
 	if !validationResult.IsValid {
 		// run validation finish functions for extensions

graphql_test.go

@@ -6,6 +6,9 @@ import (
 	"testing"
 
 	"github.com/graphql-go/graphql"
+	"github.com/graphql-go/graphql/language/ast"
+	"github.com/graphql-go/graphql/language/kinds"
+	"github.com/graphql-go/graphql/language/visitor"
 	"github.com/graphql-go/graphql/testutil"
 )
 
@@ -268,3 +271,59 @@ func TestEmptyStringIsNotNull(t *testing.T) {
 		t.Errorf("wrong result, query: %v, graphql result diff: %v", query, testutil.Diff(expected, result))
 	}
 }
+
+func TestQueryWithCustomRule(t *testing.T) {
+	// Test graphql.Do() with custom rule, it extracts query name from each
+	// Tests.
+	ruleN := len(graphql.SpecifiedRules)
+	rules := make([]graphql.ValidationRuleFn, ruleN+1)
+	copy(rules[:ruleN], graphql.SpecifiedRules)
+
+	var (
+		queryFound bool
+		queryName  string
+	)
+	rules[ruleN] = func(context *graphql.ValidationContext) *graphql.ValidationRuleInstance {
+		return &graphql.ValidationRuleInstance{
+			VisitorOpts: &visitor.VisitorOptions{
+				KindFuncMap: map[string]visitor.NamedVisitFuncs{
+					kinds.OperationDefinition: {
+						Enter: func(p visitor.VisitFuncParams) (string, interface{}) {
+							od, ok := p.Node.(*ast.OperationDefinition)
+							if ok && od.Operation == "query" {
+								queryFound = true
+								if od.Name != nil {
+									queryName = od.Name.Value
+								}
+							}
+							return visitor.ActionNoChange, nil
+						},
+					},
+				},
+			},
+		}
+	}
+
+	expectedNames := []string{
+		"HeroNameQuery",
+		"HeroNameAndFriendsQuery",
+		"HumanByIdQuery",
+	}
+
+	for i, test := range Tests {
+		queryFound, queryName = false, ""
+		params := graphql.Params{
+			Schema:          test.Schema,
+			RequestString:   test.Query,
+			VariableValues:  test.Variables,
+			ValidationRules: rules,
+		}
+		testGraphql(test, params, t)
+		if !queryFound {
+			t.Fatal("can't detect \"query\" operation by validation rule")
+		}
+		if queryName != expectedNames[i] {
+			t.Fatalf("unexpected query name: want=%s got=%s", queryName, expectedNames)
+		}
+	}
+}