simplify single case type switches

Found such switches using https://go-critic.github.io/overview#singleCaseSwitch-ref

Author: quasilyte

introspection.go

@@ -550,8 +550,7 @@ func init() {
 	TypeType.AddFieldConfig("interfaces", &Field{
 		Type: NewList(NewNonNull(TypeType)),
 		Resolve: func(p ResolveParams) (interface{}, error) {
-			switch ttype := p.Source.(type) {
-			case *Object:
+			if ttype, ok := p.Source.(*Object); ok {
 				return ttype.Interfaces(), nil
 			}
 			return nil, nil
@@ -579,8 +578,7 @@ func init() {
 		},
 		Resolve: func(p ResolveParams) (interface{}, error) {
 			includeDeprecated, _ := p.Args["includeDeprecated"].(bool)
-			switch ttype := p.Source.(type) {
-			case *Enum:
+			if ttype, ok := p.Source.(*Enum); ok {
 				if includeDeprecated {
 					return ttype.Values(), nil
 				}
@@ -599,8 +597,7 @@ func init() {
 	TypeType.AddFieldConfig("inputFields", &Field{
 		Type: NewList(NewNonNull(InputValueType)),
 		Resolve: func(p ResolveParams) (interface{}, error) {
-			switch ttype := p.Source.(type) {
-			case *InputObject:
+			if ttype, ok := p.Source.(*InputObject); ok {
 				fields := []*InputObjectField{}
 				for _, field := range ttype.Fields() {
 					fields = append(fields, field)

language/visitor/visitor.go

@@ -609,19 +609,20 @@ func VisitInParallel(visitorOptsSlice ...*VisitorOptions) *VisitorOptions {
 		Enter: func(p VisitFuncParams) (string, interface{}) {
 			for i, visitorOpts := range visitorOptsSlice {
 				if _, ok := skipping[i]; !ok {
-					switch node := p.Node.(type) {
-					case ast.Node:
-						kind := node.GetKind()
-						fn := GetVisitFn(visitorOpts, kind, false)
-						if fn != nil {
-							action, result := fn(p)
-							if action == ActionSkip {
-								skipping[i] = node
-							} else if action == ActionBreak {
-								skipping[i] = ActionBreak
-							} else if action == ActionUpdate {
-								return ActionUpdate, result
-							}
+					node, ok := p.Node.(ast.Node)
+					if !ok {
+						continue
+					}
+					kind := node.GetKind()
+					fn := GetVisitFn(visitorOpts, kind, false)
+					if fn != nil {
+						action, result := fn(p)
+						if action == ActionSkip {
+							skipping[i] = node
+						} else if action == ActionBreak {
+							skipping[i] = ActionBreak
+						} else if action == ActionUpdate {
+							return ActionUpdate, result
 						}
 					}
 				}
@@ -632,8 +633,7 @@ func VisitInParallel(visitorOptsSlice ...*VisitorOptions) *VisitorOptions {
 			for i, visitorOpts := range visitorOptsSlice {
 				skippedNode, ok := skipping[i]
 				if !ok {
-					switch node := p.Node.(type) {
-					case ast.Node:
+					if node, ok := p.Node.(ast.Node); ok {
 						kind := node.GetKind()
 						fn := GetVisitFn(visitorOpts, kind, true)
 						if fn != nil {