fix: change OperationTypeNode to enum

Changes OperationTypeNode to enum instead of a union type.
This allows developers to use the type as `OperationTypeNode.QUERY`
instead of risking to msispell the string 'query'.

Example:

Instead of having to write

`operation === 'query'`

you can instead write

`operation === OperationTypeNode.QUERY`

src/execution/execute.ts

@@ -23,6 +23,9 @@ import type {
   FieldNode,
   FragmentDefinitionNode,
 } from '../language/ast';
+
+import { OperationTypeNode } from '../language/ast';
+
 import { Kind } from '../language/kinds';
 
 import type { GraphQLSchema } from '../type/schema';
@@ -366,17 +369,17 @@ function executeOperation(
   const path = undefined;
 
   switch (operation.operation) {
-    case 'query':
+    case OperationTypeNode.QUERY:
       return executeFields(exeContext, rootType, rootValue, path, rootFields);
-    case 'mutation':
+    case OperationTypeNode.MUTATION:
       return executeFieldsSerially(
         exeContext,
         rootType,
         rootValue,
         path,
         rootFields,
       );
-    case 'subscription':
+    case OperationTypeNode.SUBSCRIPTION:
       // TODO: deprecate `subscribe` and move all logic here
       // Temporary solution until we finish merging execute and subscribe together
       return executeFields(exeContext, rootType, rootValue, path, rootFields);

src/language/ast.ts

@@ -364,7 +364,11 @@ export interface OperationDefinitionNode {
   readonly selectionSet: SelectionSetNode;
 }
 
-export type OperationTypeNode = 'query' | 'mutation' | 'subscription';
+export enum OperationTypeNode {
+  QUERY = 'query',
+  MUTATION = 'mutation',
+  SUBSCRIPTION = 'subscription'
+}
 
 export interface VariableDefinitionNode {
   readonly kind: 'VariableDefinition';

src/language/parser.ts

@@ -11,7 +11,6 @@ import type {
   DocumentNode,
   DefinitionNode,
   OperationDefinitionNode,
-  OperationTypeNode,
   VariableDefinitionNode,
   SelectionSetNode,
   SelectionNode,
@@ -63,7 +62,7 @@ import type {
   InputObjectTypeExtensionNode,
 } from './ast';
 import { Kind } from './kinds';
-import { Location } from './ast';
+import { Location, OperationTypeNode } from './ast';
 import { TokenKind } from './tokenKind';
 import { Source, isSource } from './source';
 import { DirectiveLocation } from './directiveLocation';
@@ -305,7 +304,7 @@ export class Parser {
     if (this.peek(TokenKind.BRACE_L)) {
       return this.node<OperationDefinitionNode>(start, {
         kind: Kind.OPERATION_DEFINITION,
-        operation: 'query',
+        operation: OperationTypeNode.QUERY,
         name: undefined,
         variableDefinitions: [],
         directives: [],
@@ -334,11 +333,11 @@ export class Parser {
     const operationToken = this.expectToken(TokenKind.NAME);
     switch (operationToken.value) {
       case 'query':
-        return 'query';
+        return OperationTypeNode.QUERY;
       case 'mutation':
-        return 'mutation';
+        return OperationTypeNode.MUTATION;
       case 'subscription':
-        return 'subscription';
+        return OperationTypeNode.SUBSCRIPTION;
     }
 
     throw this.unexpected(operationToken);

src/type/validate.ts

@@ -7,7 +7,6 @@ import type {
   ASTNode,
   NamedTypeNode,
   DirectiveNode,
-  OperationTypeNode,
   ObjectTypeDefinitionNode,
   ObjectTypeExtensionNode,
   InterfaceTypeDefinitionNode,
@@ -16,6 +15,8 @@ import type {
   UnionTypeExtensionNode,
 } from '../language/ast';
 
+import { OperationTypeNode } from '../language/ast';
+
 import { isEqualType, isTypeSubTypeOf } from '../utilities/typeComparators';
 
 import type { GraphQLSchema } from './schema';
@@ -120,7 +121,7 @@ function validateRootTypes(context: SchemaValidationContext): void {
       `Query root type must be Object type, it cannot be ${inspect(
         queryType,
       )}.`,
-      getOperationTypeNode(schema, 'query') ?? (queryType as any).astNode,
+      getOperationTypeNode(schema, OperationTypeNode.QUERY) ?? (queryType as any).astNode,
     );
   }
 
@@ -129,7 +130,7 @@ function validateRootTypes(context: SchemaValidationContext): void {
     context.reportError(
       'Mutation root type must be Object type if provided, it cannot be ' +
         `${inspect(mutationType)}.`,
-      getOperationTypeNode(schema, 'mutation') ?? (mutationType as any).astNode,
+      getOperationTypeNode(schema, OperationTypeNode.MUTATION) ?? (mutationType as any).astNode,
     );
   }
 
@@ -138,7 +139,7 @@ function validateRootTypes(context: SchemaValidationContext): void {
     context.reportError(
       'Subscription root type must be Object type if provided, it cannot be ' +
         `${inspect(subscriptionType)}.`,
-      getOperationTypeNode(schema, 'subscription') ??
+      getOperationTypeNode(schema, OperationTypeNode.SUBSCRIPTION) ??
         (subscriptionType as any).astNode,
     );
   }

src/validation/rules/KnownDirectivesRule.ts

@@ -4,7 +4,8 @@ import { invariant } from '../../jsutils/invariant';
 import { GraphQLError } from '../../error/GraphQLError';
 
 import type { ASTVisitor } from '../../language/visitor';
-import type { ASTNode, OperationTypeNode } from '../../language/ast';
+import type { ASTNode } from '../../language/ast';
+import { OperationTypeNode } from '../../language/ast';
 import type { DirectiveLocationEnum } from '../../language/directiveLocation';
 import { Kind } from '../../language/kinds';
 import { DirectiveLocation } from '../../language/directiveLocation';
@@ -127,11 +128,11 @@ function getDirectiveLocationForOperation(
   operation: OperationTypeNode,
 ): DirectiveLocationEnum {
   switch (operation) {
-    case 'query':
+    case OperationTypeNode.QUERY:
       return DirectiveLocation.QUERY;
-    case 'mutation':
+    case OperationTypeNode.MUTATION:
       return DirectiveLocation.MUTATION;
-    case 'subscription':
+    case OperationTypeNode.SUBSCRIPTION:
       return DirectiveLocation.SUBSCRIPTION;
   }