Backport GraphQLError toJSON method to v15 (#4324)

Eases up the transition to future v17 that has completely removed the
`formatError` utility.

src/error/GraphQLError.d.ts

@@ -82,10 +82,51 @@ export class GraphQLError extends Error {
    * Extension fields to add to the formatted error.
    */
   readonly extensions: { [key: string]: any };
+
+  toString(): string;
+
+  toJSON(): GraphQLFormattedError;
 }
 
 /**
  * Prints a GraphQLError to a string, representing useful location information
  * about the error's position in the source.
  */
 export function printError(error: GraphQLError): string;
+
+/**
+ * Given a GraphQLError, format it according to the rules described by the
+ * Response Format, Errors section of the GraphQL Specification.
+ */
+export function formatError(error: GraphQLError): GraphQLFormattedError;
+
+/**
+ * @see https://github.com/graphql/graphql-spec/blob/master/spec/Section%207%20--%20Response.md#errors
+ */
+export interface GraphQLFormattedError<
+  TExtensions extends Record<string, any> = Record<string, any>
+> {
+  /**
+   * A short, human-readable summary of the problem that **SHOULD NOT** change
+   * from occurrence to occurrence of the problem, except for purposes of
+   * localization.
+   */
+  readonly message: string;
+  /**
+   * If an error can be associated to a particular point in the requested
+   * GraphQL document, it should contain a list of locations.
+   */
+  readonly locations?: ReadonlyArray<SourceLocation>;
+  /**
+   * If an error can be associated to a particular field in the GraphQL result,
+   * it _must_ contain an entry with the key `path` that details the path of
+   * the response field which experienced the error. This allows clients to
+   * identify whether a null result is intentional or caused by a runtime error.
+   */
+  readonly path?: ReadonlyArray<string | number>;
+  /**
+   * Reserved for implementors to extend the protocol however they see fit,
+   * and hence there are no additional restrictions on its contents.
+   */
+  readonly extensions?: TExtensions;
+}

src/error/GraphQLError.js

@@ -7,6 +7,9 @@ import type { SourceLocation } from '../language/location';
 import { getLocation } from '../language/location';
 import { printLocation, printSourceLocation } from '../language/printLocation';
 
+import { formatError } from './formatError';
+import type { GraphQLFormattedError } from './formatError';
+
 /**
  * A GraphQLError describes an Error found during the parse, validate, or
  * execute phases of performing a GraphQL operation. In addition to a message
@@ -157,6 +160,10 @@ export class GraphQLError extends Error {
     return printError(this);
   }
 
+  toJSON(): GraphQLFormattedError {
+    return formatError(this);
+  }
+
   // FIXME: workaround to not break chai comparisons, should be remove in v16
   // $FlowFixMe[unsupported-syntax] Flow doesn't support computed properties yet
   get [SYMBOL_TO_STRING_TAG](): string {

src/error/__tests__/GraphQLError-test.js

@@ -293,3 +293,52 @@ describe('printError', () => {
     `);
   });
 });
+
+describe('toJSON', () => {
+  it('includes path', () => {
+    const error = new GraphQLError('msg', null, null, null, [
+      'path',
+      3,
+      'to',
+      'field',
+    ]);
+
+    expect(error.toJSON()).to.deep.equal({
+      message: 'msg',
+      locations: undefined,
+      path: ['path', 3, 'to', 'field'],
+    });
+  });
+
+  it('includes extension fields', () => {
+    const error = new GraphQLError('msg', null, null, null, null, null, {
+      foo: 'bar',
+    });
+
+    expect(error.toJSON()).to.deep.equal({
+      message: 'msg',
+      locations: undefined,
+      path: undefined,
+      extensions: { foo: 'bar' },
+    });
+  });
+
+  it('can be created with full argument list', () => {
+    const error = new GraphQLError(
+      'msg',
+      [operationNode],
+      source,
+      [6],
+      ['path', 2, 'a'],
+      new Error('I like turtles'),
+      { hee: 'I like turtles' },
+    );
+
+    expect(error.toJSON()).to.deep.equal({
+      message: 'msg',
+      locations: [{ column: 5, line: 2 }],
+      path: ['path', 2, 'a'],
+      extensions: { hee: 'I like turtles' },
+    });
+  });
+});

src/error/formatError.d.ts

@@ -1,40 +1 @@
-import { SourceLocation } from '../language/location';
-
-import { GraphQLError } from './GraphQLError';
-
-/**
- * Given a GraphQLError, format it according to the rules described by the
- * Response Format, Errors section of the GraphQL Specification.
- */
-export function formatError(error: GraphQLError): GraphQLFormattedError;
-
-/**
- * @see https://github.com/graphql/graphql-spec/blob/master/spec/Section%207%20--%20Response.md#errors
- */
-export interface GraphQLFormattedError<
-  TExtensions extends Record<string, any> = Record<string, any>
-> {
-  /**
-   * A short, human-readable summary of the problem that **SHOULD NOT** change
-   * from occurrence to occurrence of the problem, except for purposes of
-   * localization.
-   */
-  readonly message: string;
-  /**
-   * If an error can be associated to a particular point in the requested
-   * GraphQL document, it should contain a list of locations.
-   */
-  readonly locations?: ReadonlyArray<SourceLocation>;
-  /**
-   * If an error can be associated to a particular field in the GraphQL result,
-   * it _must_ contain an entry with the key `path` that details the path of
-   * the response field which experienced the error. This allows clients to
-   * identify whether a null result is intentional or caused by a runtime error.
-   */
-  readonly path?: ReadonlyArray<string | number>;
-  /**
-   * Reserved for implementors to extend the protocol however they see fit,
-   * and hence there are no additional restrictions on its contents.
-   */
-  readonly extensions?: TExtensions;
-}
+export { formatError, GraphQLFormattedError } from './GraphQLError';