visitor-test.ts

import { expect } from 'chai';
import { describe, it } from 'mocha';

import { kitchenSinkQuery } from '../../__testUtils__/kitchenSinkQuery';

import type { ASTNode } from '../ast';
import { isNode } from '../ast';
import { Kind } from '../kinds';
import { parse } from '../parser';
import { visit, visitInParallel, BREAK } from '../visitor';

function checkVisitorFnArgs(ast: any, args: any, isEdited: boolean = false) {
  const [node, key, parent, path, ancestors] = args;

  expect(node).to.be.an.instanceof(Object);
  expect(node.kind).to.be.oneOf(Object.values(Kind));

  const isRoot = key === undefined;
  if (isRoot) {
    if (!isEdited) {
      expect(node).to.equal(ast);
    }
    expect(parent).to.equal(undefined);
    expect(path).to.deep.equal([]);
    expect(ancestors).to.deep.equal([]);
    return;
  }

  expect(typeof key).to.be.oneOf(['number', 'string']);

  expect(parent).to.have.property(key);

  expect(path).to.be.an.instanceof(Array);
  expect(path[path.length - 1]).to.equal(key);

  expect(ancestors).to.be.an.instanceof(Array);
  expect(ancestors.length).to.equal(path.length - 1);

  if (!isEdited) {
    let currentNode = ast;
    for (let i = 0; i < ancestors.length; ++i) {
      expect(ancestors[i]).to.equal(currentNode);

      currentNode = currentNode[path[i]];
      expect(currentNode).to.not.equal(undefined);
    }

    expect(parent).to.equal(currentNode);
    expect(parent[key]).to.equal(node);
  }
}

function getValue(node: ASTNode) {
  // @ts-expect-error FIXME
  return node.value != null ? node.value : undefined;
}

describe('Visitor', () => {
  it('handles empty visitor', () => {
    const ast = parse('{ a }', { noLocation: true });
    expect(() => visit(ast, {})).to.not.throw();
  });

  it('validates path argument', () => {
    const visited = [];

    const ast = parse('{ a }', { noLocation: true });

    visit(ast, {
      enter(_node, _key, _parent, path) {
        checkVisitorFnArgs(ast, arguments);
        visited.push(['enter', path.slice()]);
      },
      leave(_node, _key, _parent, path) {
        checkVisitorFnArgs(ast, arguments);
        visited.push(['leave', path.slice()]);
      },
    });

    expect(visited).to.deep.equal([
      ['enter', []],
      ['enter', ['definitions', 0]],
      ['enter', ['definitions', 0, 'selectionSet']],
      ['enter', ['definitions', 0, 'selectionSet', 'selections', 0]],
      ['enter', ['definitions', 0, 'selectionSet', 'selections', 0, 'name']],
      ['leave', ['definitions', 0, 'selectionSet', 'selections', 0, 'name']],
      ['leave', ['definitions', 0, 'selectionSet', 'selections', 0]],
      ['leave', ['definitions', 0, 'selectionSet']],
      ['leave', ['definitions', 0]],
      ['leave', []],
    ]);
  });

  it('validates ancestors argument', () => {
    const ast = parse('{ a }', { noLocation: true });
    const visitedNodes = [];

    visit(ast, {
      enter(node, key, parent, _path, ancestors) {
        const inArray = typeof key === 'number';
        if (inArray) {
          visitedNodes.push(parent);
        }
        visitedNodes.push(node);

        const expectedAncestors = visitedNodes.slice(0, -2);
        expect(ancestors).to.deep.equal(expectedAncestors);
      },
      leave(_node, key, _parent, _path, ancestors) {
        const expectedAncestors = visitedNodes.slice(0, -2);
        expect(ancestors).to.deep.equal(expectedAncestors);

        const inArray = typeof key === 'number';
        if (inArray) {
          visitedNodes.pop();
        }
        visitedNodes.pop();
      },
    });
  });

  it('allows editing a node both on enter and on leave', () => {
    const ast = parse('{ a, b, c { a, b, c } }', { noLocation: true });

    let selectionSet;

    const editedAST = visit(ast, {
      OperationDefinition: {
        enter(node) {
          checkVisitorFnArgs(ast, arguments);
          selectionSet = node.selectionSet;
          return {
            ...node,
            selectionSet: {
              kind: 'SelectionSet',
              selections: [],
            },
            didEnter: true,
          };
        },
        leave(node) {
          checkVisitorFnArgs(ast, arguments, /* isEdited */ true);
          return {
            ...node,
            selectionSet,
            didLeave: true,
          };
        },
      },
    });

    expect(editedAST).to.deep.equal({
      ...ast,
      definitions: [
        {
          ...ast.definitions[0],
          didEnter: true,
          didLeave: true,
        },
      ],
    });
  });

  it('allows editing the root node on enter and on leave', () => {
    const ast = parse('{ a, b, c { a, b, c } }', { noLocation: true });

    const { definitions } = ast;

    const editedAST = visit(ast, {
      Document: {
        enter(node) {
          checkVisitorFnArgs(ast, arguments);
          return {
            ...node,
            definitions: [],
            didEnter: true,
          };
        },
        leave(node) {
          checkVisitorFnArgs(ast, arguments, /* isEdited */ true);
          return {
            ...node,
            definitions,
            didLeave: true,
          };
        },
      },
    });

    expect(editedAST).to.deep.equal({
      ...ast,
      didEnter: true,
      didLeave: true,
    });
  });

  it('allows for editing on enter', () => {
    const ast = parse('{ a, b, c { a, b, c } }', { noLocation: true });
    const editedAST = visit(ast, {
      enter(node) {
        checkVisitorFnArgs(ast, arguments);
        if (node.kind === 'Field' && node.name.value === 'b') {
          return null;
        }
      },
    });

    expect(ast).to.deep.equal(
      parse('{ a, b, c { a, b, c } }', { noLocation: true }),
    );

    expect(editedAST).to.deep.equal(
      parse('{ a,    c { a,    c } }', { noLocation: true }),
    );
  });

  it('allows for editing on leave', () => {
    const ast = parse('{ a, b, c { a, b, c } }', { noLocation: true });
    const editedAST = visit(ast, {
      leave(node) {
        checkVisitorFnArgs(ast, arguments, /* isEdited */ true);
        if (node.kind === 'Field' && node.name.value === 'b') {
          return null;
        }
      },
    });

    expect(ast).to.deep.equal(
      parse('{ a, b, c { a, b, c } }', { noLocation: true }),
    );

    expect(editedAST).to.deep.equal(
      parse('{ a,    c { a,    c } }', { noLocation: true }),
    );
  });

  it('ignores false returned on leave', () => {
    const ast = parse('{ a, b, c { a, b, c } }', { noLocation: true });
    const returnedAST = visit(ast, {
      leave() {
        return false;
      },
    });

    expect(returnedAST).to.deep.equal(
      parse('{ a, b, c { a, b, c } }', { noLocation: true }),
    );
  });

  it('visits edited node', () => {
    const addedField = {
      kind: 'Field',
      name: {
        kind: 'Name',
        value: '__typename',
      },
    };

    let didVisitAddedField;

    const ast = parse('{ a { x } }', { noLocation: true });
    visit(ast, {
      enter(node) {
        checkVisitorFnArgs(ast, arguments, /* isEdited */ true);
        if (node.kind === 'Field' && node.name.value === 'a') {
          return {
            kind: 'Field',
            // @ts-expect-error FIXME
            selectionSet: [addedField].concat(node.selectionSet),
          };
        }
        if (node === addedField) {
          didVisitAddedField = true;
        }
      },
    });

    expect(didVisitAddedField).to.equal(true);
  });

  it('allows skipping a sub-tree', () => {
    const visited = [];

    const ast = parse('{ a, b { x }, c }', { noLocation: true });
    visit(ast, {
      enter(node) {
        checkVisitorFnArgs(ast, arguments);
        visited.push(['enter', node.kind, getValue(node)]);
        if (node.kind === 'Field' && node.name.value === 'b') {
          return false;
        }
      },

      leave(node) {
        checkVisitorFnArgs(ast, arguments);
        visited.push(['leave', node.kind, getValue(node)]);
      },
    });

    expect(visited).to.deep.equal([
      ['enter', 'Document', undefined],
      ['enter', 'OperationDefinition', undefined],
      ['enter', 'SelectionSet', undefined],
      ['enter', 'Field', undefined],
      ['enter', 'Name', 'a'],
      ['leave', 'Name', 'a'],
      ['leave', 'Field', undefined],
      ['enter', 'Field', undefined],
      ['enter', 'Field', undefined],
      ['enter', 'Name', 'c'],
      ['leave', 'Name', 'c'],
      ['leave', 'Field', undefined],
      ['leave', 'SelectionSet', undefined],
      ['leave', 'OperationDefinition', undefined],
      ['leave', 'Document', undefined],
    ]);
  });

  it('allows early exit while visiting', () => {
    const visited = [];

    const ast = parse('{ a, b { x }, c }', { noLocation: true });
    visit(ast, {
      enter(node) {
        checkVisitorFnArgs(ast, arguments);
        visited.push(['enter', node.kind, getValue(node)]);
        if (node.kind === 'Name' && node.value === 'x') {
          return BREAK;
        }
      },
      leave(node) {
        checkVisitorFnArgs(ast, arguments);
        visited.push(['leave', node.kind, getValue(node)]);
      },
    });

    expect(visited).to.deep.equal([
      ['enter', 'Document', undefined],
      ['enter', 'OperationDefinition', undefined],
      ['enter', 'SelectionSet', undefined],
      ['enter', 'Field', undefined],
      ['enter', 'Name', 'a'],
      ['leave', 'Name', 'a'],
      ['leave', 'Field', undefined],
      ['enter', 'Field', undefined],
      ['enter', 'Name', 'b'],
      ['leave', 'Name', 'b'],
      ['enter', 'SelectionSet', undefined],
      ['enter', 'Field', undefined],
      ['enter', 'Name', 'x'],
    ]);
  });

  it('allows early exit while leaving', () => {
    const visited = [];

    const ast = parse('{ a, b { x }, c }', { noLocation: true });
    visit(ast, {
      enter(node) {
        checkVisitorFnArgs(ast, arguments);
        visited.push(['enter', node.kind, getValue(node)]);
      },

      leave(node) {
        checkVisitorFnArgs(ast, arguments);
        visited.push(['leave', node.kind, getValue(node)]);
        if (node.kind === 'Name' && node.value === 'x') {
          return BREAK;
        }
      },
    });

    expect(visited).to.deep.equal([
      ['enter', 'Document', undefined],
      ['enter', 'OperationDefinition', undefined],
      ['enter', 'SelectionSet', undefined],
      ['enter', 'Field', undefined],
      ['enter', 'Name', 'a'],
      ['leave', 'Name', 'a'],
      ['leave', 'Field', undefined],
      ['enter', 'Field', undefined],
      ['enter', 'Name', 'b'],
      ['leave', 'Name', 'b'],
      ['enter', 'SelectionSet', undefined],
      ['enter', 'Field', undefined],
      ['enter', 'Name', 'x'],
      ['leave', 'Name', 'x'],
    ]);
  });

  it('allows a named functions visitor API', () => {
    const visited = [];

    const ast = parse('{ a, b { x }, c }', { noLocation: true });
    visit(ast, {
      Name(node) {
        checkVisitorFnArgs(ast, arguments);
        visited.push(['enter', node.kind, getValue(node)]);
      },
      SelectionSet: {
        enter(node) {
          checkVisitorFnArgs(ast, arguments);
          visited.push(['enter', node.kind, getValue(node)]);
        },
        leave(node) {
          checkVisitorFnArgs(ast, arguments);
          visited.push(['leave', node.kind, getValue(node)]);
        },
      },
    });

    expect(visited).to.deep.equal([
      ['enter', 'SelectionSet', undefined],
      ['enter', 'Name', 'a'],
      ['enter', 'Name', 'b'],
      ['enter', 'SelectionSet', undefined],
      ['enter', 'Name', 'x'],
      ['leave', 'SelectionSet', undefined],
      ['enter', 'Name', 'c'],
      ['leave', 'SelectionSet', undefined],
    ]);
  });

  it('visit nodes with unknown kinds but does not traverse deeper', () => {
    const customAST = parse('{ a }');
    // @ts-expect-error
    customAST.definitions[0].selectionSet.selections.push({
      kind: 'CustomField',
      name: { kind: 'Name', value: 'NamedNodeToBeSkipped' },
      selectionSet: {
        kind: 'SelectionSet',
        selections: [
          {
            kind: 'CustomField',
            name: { kind: 'Name', value: 'NamedNodeToBeSkipped' },
          },
        ],
      },
    });

    const visited = [];
    visit(customAST, {
      enter(node) {
        visited.push(['enter', node.kind, getValue(node)]);
      },
      leave(node) {
        visited.push(['leave', node.kind, getValue(node)]);
      },
    });

    expect(visited).to.deep.equal([
      ['enter', 'Document', undefined],
      ['enter', 'OperationDefinition', undefined],
      ['enter', 'SelectionSet', undefined],
      ['enter', 'Field', undefined],
      ['enter', 'Name', 'a'],
      ['leave', 'Name', 'a'],
      ['leave', 'Field', undefined],
      ['enter', 'CustomField', undefined],
      ['leave', 'CustomField', undefined],
      ['leave', 'SelectionSet', undefined],
      ['leave', 'OperationDefinition', undefined],
      ['leave', 'Document', undefined],
    ]);
  });

  it('Legacy: visits variables defined in fragments', () => {
    const ast = parse('fragment a($v: Boolean = false) on t { f }', {
      noLocation: true,
      allowLegacyFragmentVariables: true,
    });
    const visited = [];

    visit(ast, {
      enter(node) {
        checkVisitorFnArgs(ast, arguments);
        visited.push(['enter', node.kind, getValue(node)]);
      },
      leave(node) {
        checkVisitorFnArgs(ast, arguments);
        visited.push(['leave', node.kind, getValue(node)]);
      },
    });

    expect(visited).to.deep.equal([
      ['enter', 'Document', undefined],
      ['enter', 'FragmentDefinition', undefined],
      ['enter', 'Name', 'a'],
      ['leave', 'Name', 'a'],
      ['enter', 'VariableDefinition', undefined],
      ['enter', 'Variable', undefined],
      ['enter', 'Name', 'v'],
      ['leave', 'Name', 'v'],
      ['leave', 'Variable', undefined],
      ['enter', 'NamedType', undefined],
      ['enter', 'Name', 'Boolean'],
      ['leave', 'Name', 'Boolean'],
      ['leave', 'NamedType', undefined],
      ['enter', 'BooleanValue', false],
      ['leave', 'BooleanValue', false],
      ['leave', 'VariableDefinition', undefined],
      ['enter', 'NamedType', undefined],
      ['enter', 'Name', 't'],
      ['leave', 'Name', 't'],
      ['leave', 'NamedType', undefined],
      ['enter', 'SelectionSet', undefined],
      ['enter', 'Field', undefined],
      ['enter', 'Name', 'f'],
      ['leave', 'Name', 'f'],
      ['leave', 'Field', undefined],
      ['leave', 'SelectionSet', undefined],
      ['leave', 'FragmentDefinition', undefined],
      ['leave', 'Document', undefined],
    ]);
  });

  it('visits kitchen sink', () => {
    const ast = parse(kitchenSinkQuery);
    const visited = [];
    const argsStack = [];

    visit(ast, {
      enter(node, key, parent) {
        visited.push([
          'enter',
          node.kind,
          key,
          isNode(parent) ? parent.kind : undefined,
        ]);

        checkVisitorFnArgs(ast, arguments);
        argsStack.push([...arguments]);
      },

      leave(node, key, parent) {
        visited.push([
          'leave',
          node.kind,
          key,
          isNode(parent) ? parent.kind : undefined,
        ]);

        expect(argsStack.pop()).to.deep.equal([...arguments]);
      },
    });

    expect(argsStack).to.deep.equal([]);
    expect(visited).to.deep.equal([
      ['enter', 'Document', undefined, undefined],
      ['enter', 'OperationDefinition', 0, undefined],
      ['enter', 'Name', 'name', 'OperationDefinition'],
      ['leave', 'Name', 'name', 'OperationDefinition'],
      ['enter', 'VariableDefinition', 0, undefined],
      ['enter', 'Variable', 'variable', 'VariableDefinition'],
      ['enter', 'Name', 'name', 'Variable'],
      ['leave', 'Name', 'name', 'Variable'],
      ['leave', 'Variable', 'variable', 'VariableDefinition'],
      ['enter', 'NamedType', 'type', 'VariableDefinition'],
      ['enter', 'Name', 'name', 'NamedType'],
      ['leave', 'Name', 'name', 'NamedType'],
      ['leave', 'NamedType', 'type', 'VariableDefinition'],
      ['leave', 'VariableDefinition', 0, undefined],
      ['enter', 'VariableDefinition', 1, undefined],
      ['enter', 'Variable', 'variable', 'VariableDefinition'],
      ['enter', 'Name', 'name', 'Variable'],
      ['leave', 'Name', 'name', 'Variable'],
      ['leave', 'Variable', 'variable', 'VariableDefinition'],
      ['enter', 'NamedType', 'type', 'VariableDefinition'],
      ['enter', 'Name', 'name', 'NamedType'],
      ['leave', 'Name', 'name', 'NamedType'],
      ['leave', 'NamedType', 'type', 'VariableDefinition'],
      ['enter', 'EnumValue', 'defaultValue', 'VariableDefinition'],
      ['leave', 'EnumValue', 'defaultValue', 'VariableDefinition'],
      ['leave', 'VariableDefinition', 1, undefined],
      ['enter', 'Directive', 0, undefined],
      ['enter', 'Name', 'name', 'Directive'],
      ['leave', 'Name', 'name', 'Directive'],
      ['leave', 'Directive', 0, undefined],
      ['enter', 'SelectionSet', 'selectionSet', 'OperationDefinition'],
      ['enter', 'Field', 0, undefined],
      ['enter', 'Name', 'alias', 'Field'],
      ['leave', 'Name', 'alias', 'Field'],
      ['enter', 'Name', 'name', 'Field'],
      ['leave', 'Name', 'name', 'Field'],
      ['enter', 'Argument', 0, undefined],
      ['enter', 'Name', 'name', 'Argument'],
      ['leave', 'Name', 'name', 'Argument'],
      ['enter', 'ListValue', 'value', 'Argument'],
      ['enter', 'IntValue', 0, undefined],
      ['leave', 'IntValue', 0, undefined],
      ['enter', 'IntValue', 1, undefined],
      ['leave', 'IntValue', 1, undefined],
      ['leave', 'ListValue', 'value', 'Argument'],
      ['leave', 'Argument', 0, undefined],
      ['enter', 'SelectionSet', 'selectionSet', 'Field'],
      ['enter', 'Field', 0, undefined],
      ['enter', 'Name', 'name', 'Field'],
      ['leave', 'Name', 'name', 'Field'],
      ['leave', 'Field', 0, undefined],
      ['enter', 'InlineFragment', 1, undefined],
      ['enter', 'NamedType', 'typeCondition', 'InlineFragment'],
      ['enter', 'Name', 'name', 'NamedType'],
      ['leave', 'Name', 'name', 'NamedType'],
      ['leave', 'NamedType', 'typeCondition', 'InlineFragment'],
      ['enter', 'Directive', 0, undefined],
      ['enter', 'Name', 'name', 'Directive'],
      ['leave', 'Name', 'name', 'Directive'],
      ['leave', 'Directive', 0, undefined],
      ['enter', 'SelectionSet', 'selectionSet', 'InlineFragment'],
      ['enter', 'Field', 0, undefined],
      ['enter', 'Name', 'name', 'Field'],
      ['leave', 'Name', 'name', 'Field'],
      ['enter', 'SelectionSet', 'selectionSet', 'Field'],
      ['enter', 'Field', 0, undefined],
      ['enter', 'Name', 'name', 'Field'],
      ['leave', 'Name', 'name', 'Field'],
      ['leave', 'Field', 0, undefined],
      ['enter', 'Field', 1, undefined],
      ['enter', 'Name', 'alias', 'Field'],
      ['leave', 'Name', 'alias', 'Field'],
      ['enter', 'Name', 'name', 'Field'],
      ['leave', 'Name', 'name', 'Field'],
      ['enter', 'Argument', 0, undefined],
      ['enter', 'Name', 'name', 'Argument'],
      ['leave', 'Name', 'name', 'Argument'],
      ['enter', 'IntValue', 'value', 'Argument'],
      ['leave', 'IntValue', 'value', 'Argument'],
      ['leave', 'Argument', 0, undefined],
      ['enter', 'Argument', 1, undefined],
      ['enter', 'Name', 'name', 'Argument'],
      ['leave', 'Name', 'name', 'Argument'],
      ['enter', 'Variable', 'value', 'Argument'],
      ['enter', 'Name', 'name', 'Variable'],
      ['leave', 'Name', 'name', 'Variable'],
      ['leave', 'Variable', 'value', 'Argument'],
      ['leave', 'Argument', 1, undefined],
      ['enter', 'Directive', 0, undefined],
      ['enter', 'Name', 'name', 'Directive'],
      ['leave', 'Name', 'name', 'Directive'],
      ['enter', 'Argument', 0, undefined],
      ['enter', 'Name', 'name', 'Argument'],
      ['leave', 'Name', 'name', 'Argument'],
      ['enter', 'Variable', 'value', 'Argument'],
      ['enter', 'Name', 'name', 'Variable'],
      ['leave', 'Name', 'name', 'Variable'],
      ['leave', 'Variable', 'value', 'Argument'],
      ['leave', 'Argument', 0, undefined],
      ['leave', 'Directive', 0, undefined],
      ['enter', 'SelectionSet', 'selectionSet', 'Field'],
      ['enter', 'Field', 0, undefined],
      ['enter', 'Name', 'name', 'Field'],
      ['leave', 'Name', 'name', 'Field'],
      ['leave', 'Field', 0, undefined],
      ['enter', 'FragmentSpread', 1, undefined],
      ['enter', 'Name', 'name', 'FragmentSpread'],
      ['leave', 'Name', 'name', 'FragmentSpread'],
      ['enter', 'Directive', 0, undefined],
      ['enter', 'Name', 'name', 'Directive'],
      ['leave', 'Name', 'name', 'Directive'],
      ['leave', 'Directive', 0, undefined],
      ['leave', 'FragmentSpread', 1, undefined],
      ['leave', 'SelectionSet', 'selectionSet', 'Field'],
      ['leave', 'Field', 1, undefined],
      ['leave', 'SelectionSet', 'selectionSet', 'Field'],
      ['leave', 'Field', 0, undefined],
      ['leave', 'SelectionSet', 'selectionSet', 'InlineFragment'],
      ['leave', 'InlineFragment', 1, undefined],
      ['enter', 'InlineFragment', 2, undefined],
      ['enter', 'Directive', 0, undefined],
      ['enter', 'Name', 'name', 'Directive'],
      ['leave', 'Name', 'name', 'Directive'],
      ['enter', 'Argument', 0, undefined],
      ['enter', 'Name', 'name', 'Argument'],
      ['leave', 'Name', 'name', 'Argument'],
      ['enter', 'Variable', 'value', 'Argument'],
      ['enter', 'Name', 'name', 'Variable'],
      ['leave', 'Name', 'name', 'Variable'],
      ['leave', 'Variable', 'value', 'Argument'],
      ['leave', 'Argument', 0, undefined],
      ['leave', 'Directive', 0, undefined],
      ['enter', 'SelectionSet', 'selectionSet', 'InlineFragment'],
      ['enter', 'Field', 0, undefined],
      ['enter', 'Name', 'name', 'Field'],
      ['leave', 'Name', 'name', 'Field'],
      ['leave', 'Field', 0, undefined],
      ['leave', 'SelectionSet', 'selectionSet', 'InlineFragment'],
      ['leave', 'InlineFragment', 2, undefined],
      ['enter', 'InlineFragment', 3, undefined],
      ['enter', 'SelectionSet', 'selectionSet', 'InlineFragment'],
      ['enter', 'Field', 0, undefined],
      ['enter', 'Name', 'name', 'Field'],
      ['leave', 'Name', 'name', 'Field'],
      ['leave', 'Field', 0, undefined],
      ['leave', 'SelectionSet', 'selectionSet', 'InlineFragment'],
      ['leave', 'InlineFragment', 3, undefined],
      ['leave', 'SelectionSet', 'selectionSet', 'Field'],
      ['leave', 'Field', 0, undefined],
      ['leave', 'SelectionSet', 'selectionSet', 'OperationDefinition'],
      ['leave', 'OperationDefinition', 0, undefined],
      ['enter', 'OperationDefinition', 1, undefined],
      ['enter', 'Name', 'name', 'OperationDefinition'],
      ['leave', 'Name', 'name', 'OperationDefinition'],
      ['enter', 'Directive', 0, undefined],
      ['enter', 'Name', 'name', 'Directive'],
      ['leave', 'Name', 'name', 'Directive'],
      ['leave', 'Directive', 0, undefined],
      ['enter', 'SelectionSet', 'selectionSet', 'OperationDefinition'],
      ['enter', 'Field', 0, undefined],
      ['enter', 'Name', 'name', 'Field'],
      ['leave', 'Name', 'name', 'Field'],
      ['enter', 'Argument', 0, undefined],
      ['enter', 'Name', 'name', 'Argument'],
      ['leave', 'Name', 'name', 'Argument'],
      ['enter', 'IntValue', 'value', 'Argument'],
      ['leave', 'IntValue', 'value', 'Argument'],
      ['leave', 'Argument', 0, undefined],
      ['enter', 'Directive', 0, undefined],
      ['enter', 'Name', 'name', 'Directive'],
      ['leave', 'Name', 'name', 'Directive'],
      ['leave', 'Directive', 0, undefined],
      ['enter', 'SelectionSet', 'selectionSet', 'Field'],
      ['enter', 'Field', 0, undefined],
      ['enter', 'Name', 'name', 'Field'],
      ['leave', 'Name', 'name', 'Field'],
      ['enter', 'SelectionSet', 'selectionSet', 'Field'],
      ['enter', 'Field', 0, undefined],
      ['enter', 'Name', 'name', 'Field'],
      ['leave', 'Name', 'name', 'Field'],
      ['enter', 'Directive', 0, undefined],
      ['enter', 'Name', 'name', 'Directive'],
      ['leave', 'Name', 'name', 'Directive'],
      ['leave', 'Directive', 0, undefined],
      ['leave', 'Field', 0, undefined],
      ['leave', 'SelectionSet', 'selectionSet', 'Field'],
      ['leave', 'Field', 0, undefined],
      ['leave', 'SelectionSet', 'selectionSet', 'Field'],
      ['leave', 'Field', 0, undefined],
      ['leave', 'SelectionSet', 'selectionSet', 'OperationDefinition'],
      ['leave', 'OperationDefinition', 1, undefined],
      ['enter', 'OperationDefinition', 2, undefined],
      ['enter', 'Name', 'name', 'OperationDefinition'],
      ['leave', 'Name', 'name', 'OperationDefinition'],
      ['enter', 'VariableDefinition', 0, undefined],
      ['enter', 'Variable', 'variable', 'VariableDefinition'],
      ['enter', 'Name', 'name', 'Variable'],
      ['leave', 'Name', 'name', 'Variable'],
      ['leave', 'Variable', 'variable', 'VariableDefinition'],
      ['enter', 'NamedType', 'type', 'VariableDefinition'],
      ['enter', 'Name', 'name', 'NamedType'],
      ['leave', 'Name', 'name', 'NamedType'],
      ['leave', 'NamedType', 'type', 'VariableDefinition'],
      ['leave', 'VariableDefinition', 0, undefined],
      ['enter', 'Directive', 0, undefined],
      ['enter', 'Name', 'name', 'Directive'],
      ['leave', 'Name', 'name', 'Directive'],
      ['leave', 'Directive', 0, undefined],
      ['enter', 'SelectionSet', 'selectionSet', 'OperationDefinition'],
      ['enter', 'Field', 0, undefined],
      ['enter', 'Name', 'name', 'Field'],
      ['leave', 'Name', 'name', 'Field'],
      ['enter', 'Argument', 0, undefined],
      ['enter', 'Name', 'name', 'Argument'],
      ['leave', 'Name', 'name', 'Argument'],
      ['enter', 'Variable', 'value', 'Argument'],
      ['enter', 'Name', 'name', 'Variable'],
      ['leave', 'Name', 'name', 'Variable'],
      ['leave', 'Variable', 'value', 'Argument'],
      ['leave', 'Argument', 0, undefined],
      ['enter', 'SelectionSet', 'selectionSet', 'Field'],
      ['enter', 'Field', 0, undefined],
      ['enter', 'Name', 'name', 'Field'],
      ['leave', 'Name', 'name', 'Field'],
      ['enter', 'SelectionSet', 'selectionSet', 'Field'],
      ['enter', 'Field', 0, undefined],
      ['enter', 'Name', 'name', 'Field'],
      ['leave', 'Name', 'name', 'Field'],
      ['enter', 'SelectionSet', 'selectionSet', 'Field'],
      ['enter', 'Field', 0, undefined],
      ['enter', 'Name', 'name', 'Field'],
      ['leave', 'Name', 'name', 'Field'],
      ['leave', 'Field', 0, undefined],
      ['leave', 'SelectionSet', 'selectionSet', 'Field'],
      ['leave', 'Field', 0, undefined],
      ['enter', 'Field', 1, undefined],
      ['enter', 'Name', 'name', 'Field'],
      ['leave', 'Name', 'name', 'Field'],
      ['enter', 'SelectionSet', 'selectionSet', 'Field'],
      ['enter', 'Field', 0, undefined],
      ['enter', 'Name', 'name', 'Field'],
      ['leave', 'Name', 'name', 'Field'],
      ['leave', 'Field', 0, undefined],
      ['leave', 'SelectionSet', 'selectionSet', 'Field'],
      ['leave', 'Field', 1, undefined],
      ['leave', 'SelectionSet', 'selectionSet', 'Field'],
      ['leave', 'Field', 0, undefined],
      ['leave', 'SelectionSet', 'selectionSet', 'Field'],
      ['leave', 'Field', 0, undefined],
      ['leave', 'SelectionSet', 'selectionSet', 'OperationDefinition'],
      ['leave', 'OperationDefinition', 2, undefined],
      ['enter', 'FragmentDefinition', 3, undefined],
      ['enter', 'Name', 'name', 'FragmentDefinition'],
      ['leave', 'Name', 'name', 'FragmentDefinition'],
      ['enter', 'NamedType', 'typeCondition', 'FragmentDefinition'],
      ['enter', 'Name', 'name', 'NamedType'],
      ['leave', 'Name', 'name', 'NamedType'],
      ['leave', 'NamedType', 'typeCondition', 'FragmentDefinition'],
      ['enter', 'Directive', 0, undefined],
      ['enter', 'Name', 'name', 'Directive'],
      ['leave', 'Name', 'name', 'Directive'],
      ['leave', 'Directive', 0, undefined],
      ['enter', 'SelectionSet', 'selectionSet', 'FragmentDefinition'],
      ['enter', 'Field', 0, undefined],
      ['enter', 'Name', 'name', 'Field'],
      ['leave', 'Name', 'name', 'Field'],
      ['enter', 'Argument', 0, undefined],
      ['enter', 'Name', 'name', 'Argument'],
      ['leave', 'Name', 'name', 'Argument'],
      ['enter', 'Variable', 'value', 'Argument'],
      ['enter', 'Name', 'name', 'Variable'],
      ['leave', 'Name', 'name', 'Variable'],
      ['leave', 'Variable', 'value', 'Argument'],
      ['leave', 'Argument', 0, undefined],
      ['enter', 'Argument', 1, undefined],
      ['enter', 'Name', 'name', 'Argument'],
      ['leave', 'Name', 'name', 'Argument'],
      ['enter', 'Variable', 'value', 'Argument'],
      ['enter', 'Name', 'name', 'Variable'],
      ['leave', 'Name', 'name', 'Variable'],
      ['leave', 'Variable', 'value', 'Argument'],
      ['leave', 'Argument', 1, undefined],
      ['enter', 'Argument', 2, undefined],
      ['enter', 'Name', 'name', 'Argument'],
      ['leave', 'Name', 'name', 'Argument'],
      ['enter', 'ObjectValue', 'value', 'Argument'],
      ['enter', 'ObjectField', 0, undefined],
      ['enter', 'Name', 'name', 'ObjectField'],
      ['leave', 'Name', 'name', 'ObjectField'],
      ['enter', 'StringValue', 'value', 'ObjectField'],
      ['leave', 'StringValue', 'value', 'ObjectField'],
      ['leave', 'ObjectField', 0, undefined],
      ['enter', 'ObjectField', 1, undefined],
      ['enter', 'Name', 'name', 'ObjectField'],
      ['leave', 'Name', 'name', 'ObjectField'],
      ['enter', 'StringValue', 'value', 'ObjectField'],
      ['leave', 'StringValue', 'value', 'ObjectField'],
      ['leave', 'ObjectField', 1, undefined],
      ['leave', 'ObjectValue', 'value', 'Argument'],
      ['leave', 'Argument', 2, undefined],
      ['leave', 'Field', 0, undefined],
      ['leave', 'SelectionSet', 'selectionSet', 'FragmentDefinition'],
      ['leave', 'FragmentDefinition', 3, undefined],
      ['enter', 'OperationDefinition', 4, undefined],
      ['enter', 'SelectionSet', 'selectionSet', 'OperationDefinition'],
      ['enter', 'Field', 0, undefined],
      ['enter', 'Name', 'name', 'Field'],
      ['leave', 'Name', 'name', 'Field'],
      ['enter', 'Argument', 0, undefined],
      ['enter', 'Name', 'name', 'Argument'],
      ['leave', 'Name', 'name', 'Argument'],
      ['enter', 'BooleanValue', 'value', 'Argument'],
      ['leave', 'BooleanValue', 'value', 'Argument'],
      ['leave', 'Argument', 0, undefined],
      ['enter', 'Argument', 1, undefined],
      ['enter', 'Name', 'name', 'Argument'],
      ['leave', 'Name', 'name', 'Argument'],
      ['enter', 'BooleanValue', 'value', 'Argument'],
      ['leave', 'BooleanValue', 'value', 'Argument'],
      ['leave', 'Argument', 1, undefined],
      ['enter', 'Argument', 2, undefined],
      ['enter', 'Name', 'name', 'Argument'],
      ['leave', 'Name', 'name', 'Argument'],
      ['enter', 'NullValue', 'value', 'Argument'],
      ['leave', 'NullValue', 'value', 'Argument'],
      ['leave', 'Argument', 2, undefined],
      ['leave', 'Field', 0, undefined],
      ['enter', 'Field', 1, undefined],
      ['enter', 'Name', 'name', 'Field'],
      ['leave', 'Name', 'name', 'Field'],
      ['leave', 'Field', 1, undefined],
      ['leave', 'SelectionSet', 'selectionSet', 'OperationDefinition'],
      ['leave', 'OperationDefinition', 4, undefined],
      ['enter', 'OperationDefinition', 5, undefined],
      ['enter', 'SelectionSet', 'selectionSet', 'OperationDefinition'],
      ['enter', 'Field', 0, undefined],
      ['enter', 'Name', 'name', 'Field'],
      ['leave', 'Name', 'name', 'Field'],
      ['leave', 'Field', 0, undefined],
      ['leave', 'SelectionSet', 'selectionSet', 'OperationDefinition'],
      ['leave', 'OperationDefinition', 5, undefined],
      ['leave', 'Document', undefined, undefined],
    ]);
  });

  describe('visitInParallel', () => {
    // Note: nearly identical to the above test of the same test but
    // using visitInParallel.
    it('allows skipping a sub-tree', () => {
      const visited = [];

      const ast = parse('{ a, b { x }, c }');
      visit(
        ast,
        visitInParallel([
          {
            enter(node) {
              checkVisitorFnArgs(ast, arguments);
              visited.push(['enter', node.kind, getValue(node)]);
              if (node.kind === 'Field' && node.name.value === 'b') {
                return false;
              }
            },

            leave(node) {
              checkVisitorFnArgs(ast, arguments);
              visited.push(['leave', node.kind, getValue(node)]);
            },
          },
        ]),
      );

      expect(visited).to.deep.equal([
        ['enter', 'Document', undefined],
        ['enter', 'OperationDefinition', undefined],
        ['enter', 'SelectionSet', undefined],
        ['enter', 'Field', undefined],
        ['enter', 'Name', 'a'],
        ['leave', 'Name', 'a'],
        ['leave', 'Field', undefined],
        ['enter', 'Field', undefined],
        ['enter', 'Field', undefined],
        ['enter', 'Name', 'c'],
        ['leave', 'Name', 'c'],
        ['leave', 'Field', undefined],
        ['leave', 'SelectionSet', undefined],
        ['leave', 'OperationDefinition', undefined],
        ['leave', 'Document', undefined],
      ]);
    });

    it('allows skipping different sub-trees', () => {
      const visited = [];

      const ast = parse('{ a { x }, b { y} }');
      visit(
        ast,
        visitInParallel([
          {
            enter(node) {
              checkVisitorFnArgs(ast, arguments);
              visited.push(['no-a', 'enter', node.kind, getValue(node)]);
              if (node.kind === 'Field' && node.name.value === 'a') {
                return false;
              }
            },
            leave(node) {
              checkVisitorFnArgs(ast, arguments);
              visited.push(['no-a', 'leave', node.kind, getValue(node)]);
            },
          },
          {
            enter(node) {
              checkVisitorFnArgs(ast, arguments);
              visited.push(['no-b', 'enter', node.kind, getValue(node)]);
              if (node.kind === 'Field' && node.name.value === 'b') {
                return false;
              }
            },
            leave(node) {
              checkVisitorFnArgs(ast, arguments);
              visited.push(['no-b', 'leave', node.kind, getValue(node)]);
            },
          },
        ]),
      );

      expect(visited).to.deep.equal([
        ['no-a', 'enter', 'Document', undefined],
        ['no-b', 'enter', 'Document', undefined],
        ['no-a', 'enter', 'OperationDefinition', undefined],
        ['no-b', 'enter', 'OperationDefinition', undefined],
        ['no-a', 'enter', 'SelectionSet', undefined],
        ['no-b', 'enter', 'SelectionSet', undefined],
        ['no-a', 'enter', 'Field', undefined],
        ['no-b', 'enter', 'Field', undefined],
        ['no-b', 'enter', 'Name', 'a'],
        ['no-b', 'leave', 'Name', 'a'],
        ['no-b', 'enter', 'SelectionSet', undefined],
        ['no-b', 'enter', 'Field', undefined],
        ['no-b', 'enter', 'Name', 'x'],
        ['no-b', 'leave', 'Name', 'x'],
        ['no-b', 'leave', 'Field', undefined],
        ['no-b', 'leave', 'SelectionSet', undefined],
        ['no-b', 'leave', 'Field', undefined],
        ['no-a', 'enter', 'Field', undefined],
        ['no-b', 'enter', 'Field', undefined],
        ['no-a', 'enter', 'Name', 'b'],
        ['no-a', 'leave', 'Name', 'b'],
        ['no-a', 'enter', 'SelectionSet', undefined],
        ['no-a', 'enter', 'Field', undefined],
        ['no-a', 'enter', 'Name', 'y'],
        ['no-a', 'leave', 'Name', 'y'],
        ['no-a', 'leave', 'Field', undefined],
        ['no-a', 'leave', 'SelectionSet', undefined],
        ['no-a', 'leave', 'Field', undefined],
        ['no-a', 'leave', 'SelectionSet', undefined],
        ['no-b', 'leave', 'SelectionSet', undefined],
        ['no-a', 'leave', 'OperationDefinition', undefined],
        ['no-b', 'leave', 'OperationDefinition', undefined],
        ['no-a', 'leave', 'Document', undefined],
        ['no-b', 'leave', 'Document', undefined],
      ]);
    });

    // Note: nearly identical to the above test of the same test but
    // using visitInParallel.
    it('allows early exit while visiting', () => {
      const visited = [];

      const ast = parse('{ a, b { x }, c }');
      visit(
        ast,
        visitInParallel([
          {
            enter(node) {
              checkVisitorFnArgs(ast, arguments);
              visited.push(['enter', node.kind, getValue(node)]);
              if (node.kind === 'Name' && node.value === 'x') {
                return BREAK;
              }
            },
            leave(node) {
              checkVisitorFnArgs(ast, arguments);
              visited.push(['leave', node.kind, getValue(node)]);
            },
          },
        ]),
      );

      expect(visited).to.deep.equal([
        ['enter', 'Document', undefined],
        ['enter', 'OperationDefinition', undefined],
        ['enter', 'SelectionSet', undefined],
        ['enter', 'Field', undefined],
        ['enter', 'Name', 'a'],
        ['leave', 'Name', 'a'],
        ['leave', 'Field', undefined],
        ['enter', 'Field', undefined],
        ['enter', 'Name', 'b'],
        ['leave', 'Name', 'b'],
        ['enter', 'SelectionSet', undefined],
        ['enter', 'Field', undefined],
        ['enter', 'Name', 'x'],
      ]);
    });

    it('allows early exit from different points', () => {
      const visited = [];

      const ast = parse('{ a { y }, b { x } }');
      visit(
        ast,
        visitInParallel([
          {
            enter(node) {
              checkVisitorFnArgs(ast, arguments);
              visited.push(['break-a', 'enter', node.kind, getValue(node)]);
              if (node.kind === 'Name' && node.value === 'a') {
                return BREAK;
              }
            },
            // istanbul ignore next (Never called and used as a placeholder)
            leave() {
              expect.fail('Should not be called');
            },
          },
          {
            enter(node) {
              checkVisitorFnArgs(ast, arguments);
              visited.push(['break-b', 'enter', node.kind, getValue(node)]);
              if (node.kind === 'Name' && node.value === 'b') {
                return BREAK;
              }
            },
            leave(node) {
              checkVisitorFnArgs(ast, arguments);
              visited.push(['break-b', 'leave', node.kind, getValue(node)]);
            },
          },
        ]),
      );

      expect(visited).to.deep.equal([
        ['break-a', 'enter', 'Document', undefined],
        ['break-b', 'enter', 'Document', undefined],
        ['break-a', 'enter', 'OperationDefinition', undefined],
        ['break-b', 'enter', 'OperationDefinition', undefined],
        ['break-a', 'enter', 'SelectionSet', undefined],
        ['break-b', 'enter', 'SelectionSet', undefined],
        ['break-a', 'enter', 'Field', undefined],
        ['break-b', 'enter', 'Field', undefined],
        ['break-a', 'enter', 'Name', 'a'],
        ['break-b', 'enter', 'Name', 'a'],
        ['break-b', 'leave', 'Name', 'a'],
        ['break-b', 'enter', 'SelectionSet', undefined],
        ['break-b', 'enter', 'Field', undefined],
        ['break-b', 'enter', 'Name', 'y'],
        ['break-b', 'leave', 'Name', 'y'],
        ['break-b', 'leave', 'Field', undefined],
        ['break-b', 'leave', 'SelectionSet', undefined],
        ['break-b', 'leave', 'Field', undefined],
        ['break-b', 'enter', 'Field', undefined],
        ['break-b', 'enter', 'Name', 'b'],
      ]);
    });

    // Note: nearly identical to the above test of the same test but
    // using visitInParallel.
    it('allows early exit while leaving', () => {
      const visited = [];

      const ast = parse('{ a, b { x }, c }');
      visit(
        ast,
        visitInParallel([
          {
            enter(node) {
              checkVisitorFnArgs(ast, arguments);
              visited.push(['enter', node.kind, getValue(node)]);
            },
            leave(node) {
              checkVisitorFnArgs(ast, arguments);
              visited.push(['leave', node.kind, getValue(node)]);
              if (node.kind === 'Name' && node.value === 'x') {
                return BREAK;
              }
            },
          },
        ]),
      );

      expect(visited).to.deep.equal([
        ['enter', 'Document', undefined],
        ['enter', 'OperationDefinition', undefined],
        ['enter', 'SelectionSet', undefined],
        ['enter', 'Field', undefined],
        ['enter', 'Name', 'a'],
        ['leave', 'Name', 'a'],
        ['leave', 'Field', undefined],
        ['enter', 'Field', undefined],
        ['enter', 'Name', 'b'],
        ['leave', 'Name', 'b'],
        ['enter', 'SelectionSet', undefined],
        ['enter', 'Field', undefined],
        ['enter', 'Name', 'x'],
        ['leave', 'Name', 'x'],
      ]);
    });

    it('allows early exit from leaving different points', () => {
      const visited = [];

      const ast = parse('{ a { y }, b { x } }');
      visit(
        ast,
        visitInParallel([
          {
            enter(node) {
              checkVisitorFnArgs(ast, arguments);
              visited.push(['break-a', 'enter', node.kind, getValue(node)]);
            },
            leave(node) {
              checkVisitorFnArgs(ast, arguments);
              visited.push(['break-a', 'leave', node.kind, getValue(node)]);
              if (node.kind === 'Field' && node.name.value === 'a') {
                return BREAK;
              }
            },
          },
          {
            enter(node) {
              checkVisitorFnArgs(ast, arguments);
              visited.push(['break-b', 'enter', node.kind, getValue(node)]);
            },
            leave(node) {
              checkVisitorFnArgs(ast, arguments);
              visited.push(['break-b', 'leave', node.kind, getValue(node)]);
              if (node.kind === 'Field' && node.name.value === 'b') {
                return BREAK;
              }
            },
          },
        ]),
      );

      expect(visited).to.deep.equal([
        ['break-a', 'enter', 'Document', undefined],
        ['break-b', 'enter', 'Document', undefined],
        ['break-a', 'enter', 'OperationDefinition', undefined],
        ['break-b', 'enter', 'OperationDefinition', undefined],
        ['break-a', 'enter', 'SelectionSet', undefined],
        ['break-b', 'enter', 'SelectionSet', undefined],
        ['break-a', 'enter', 'Field', undefined],
        ['break-b', 'enter', 'Field', undefined],
        ['break-a', 'enter', 'Name', 'a'],
        ['break-b', 'enter', 'Name', 'a'],
        ['break-a', 'leave', 'Name', 'a'],
        ['break-b', 'leave', 'Name', 'a'],
        ['break-a', 'enter', 'SelectionSet', undefined],
        ['break-b', 'enter', 'SelectionSet', undefined],
        ['break-a', 'enter', 'Field', undefined],
        ['break-b', 'enter', 'Field', undefined],
        ['break-a', 'enter', 'Name', 'y'],
        ['break-b', 'enter', 'Name', 'y'],
        ['break-a', 'leave', 'Name', 'y'],
        ['break-b', 'leave', 'Name', 'y'],
        ['break-a', 'leave', 'Field', undefined],
        ['break-b', 'leave', 'Field', undefined],
        ['break-a', 'leave', 'SelectionSet', undefined],
        ['break-b', 'leave', 'SelectionSet', undefined],
        ['break-a', 'leave', 'Field', undefined],
        ['break-b', 'leave', 'Field', undefined],
        ['break-b', 'enter', 'Field', undefined],
        ['break-b', 'enter', 'Name', 'b'],
        ['break-b', 'leave', 'Name', 'b'],
        ['break-b', 'enter', 'SelectionSet', undefined],
        ['break-b', 'enter', 'Field', undefined],
        ['break-b', 'enter', 'Name', 'x'],
        ['break-b', 'leave', 'Name', 'x'],
        ['break-b', 'leave', 'Field', undefined],
        ['break-b', 'leave', 'SelectionSet', undefined],
        ['break-b', 'leave', 'Field', undefined],
      ]);
    });

    it('allows for editing on enter', () => {
      const visited = [];

      const ast = parse('{ a, b, c { a, b, c } }', { noLocation: true });
      const editedAST = visit(
        ast,
        visitInParallel([
          {
            enter(node) {
              checkVisitorFnArgs(ast, arguments);
              if (node.kind === 'Field' && node.name.value === 'b') {
                return null;
              }
            },
          },
          {
            enter(node) {
              checkVisitorFnArgs(ast, arguments);
              visited.push(['enter', node.kind, getValue(node)]);
            },
            leave(node) {
              checkVisitorFnArgs(ast, arguments, /* isEdited */ true);
              visited.push(['leave', node.kind, getValue(node)]);
            },
          },
        ]),
      );

      expect(ast).to.deep.equal(
        parse('{ a, b, c { a, b, c } }', { noLocation: true }),
      );

      expect(editedAST).to.deep.equal(
        parse('{ a,    c { a,    c } }', { noLocation: true }),
      );

      expect(visited).to.deep.equal([
        ['enter', 'Document', undefined],
        ['enter', 'OperationDefinition', undefined],
        ['enter', 'SelectionSet', undefined],
        ['enter', 'Field', undefined],
        ['enter', 'Name', 'a'],
        ['leave', 'Name', 'a'],
        ['leave', 'Field', undefined],
        ['enter', 'Field', undefined],
        ['enter', 'Name', 'c'],
        ['leave', 'Name', 'c'],
        ['enter', 'SelectionSet', undefined],
        ['enter', 'Field', undefined],
        ['enter', 'Name', 'a'],
        ['leave', 'Name', 'a'],
        ['leave', 'Field', undefined],
        ['enter', 'Field', undefined],
        ['enter', 'Name', 'c'],
        ['leave', 'Name', 'c'],
        ['leave', 'Field', undefined],
        ['leave', 'SelectionSet', undefined],
        ['leave', 'Field', undefined],
        ['leave', 'SelectionSet', undefined],
        ['leave', 'OperationDefinition', undefined],
        ['leave', 'Document', undefined],
      ]);
    });

    it('allows for editing on leave', () => {
      const visited = [];

      const ast = parse('{ a, b, c { a, b, c } }', { noLocation: true });
      const editedAST = visit(
        ast,
        visitInParallel([
          {
            leave(node) {
              checkVisitorFnArgs(ast, arguments, /* isEdited */ true);
              if (node.kind === 'Field' && node.name.value === 'b') {
                return null;
              }
            },
          },
          {
            enter(node) {
              checkVisitorFnArgs(ast, arguments);
              visited.push(['enter', node.kind, getValue(node)]);
            },
            leave(node) {
              checkVisitorFnArgs(ast, arguments, /* isEdited */ true);
              visited.push(['leave', node.kind, getValue(node)]);
            },
          },
        ]),
      );

      expect(ast).to.deep.equal(
        parse('{ a, b, c { a, b, c } }', { noLocation: true }),
      );

      expect(editedAST).to.deep.equal(
        parse('{ a,    c { a,    c } }', { noLocation: true }),
      );

      expect(visited).to.deep.equal([
        ['enter', 'Document', undefined],
        ['enter', 'OperationDefinition', undefined],
        ['enter', 'SelectionSet', undefined],
        ['enter', 'Field', undefined],
        ['enter', 'Name', 'a'],
        ['leave', 'Name', 'a'],
        ['leave', 'Field', undefined],
        ['enter', 'Field', undefined],
        ['enter', 'Name', 'b'],
        ['leave', 'Name', 'b'],
        ['enter', 'Field', undefined],
        ['enter', 'Name', 'c'],
        ['leave', 'Name', 'c'],
        ['enter', 'SelectionSet', undefined],
        ['enter', 'Field', undefined],
        ['enter', 'Name', 'a'],
        ['leave', 'Name', 'a'],
        ['leave', 'Field', undefined],
        ['enter', 'Field', undefined],
        ['enter', 'Name', 'b'],
        ['leave', 'Name', 'b'],
        ['enter', 'Field', undefined],
        ['enter', 'Name', 'c'],
        ['leave', 'Name', 'c'],
        ['leave', 'Field', undefined],
        ['leave', 'SelectionSet', undefined],
        ['leave', 'Field', undefined],
        ['leave', 'SelectionSet', undefined],
        ['leave', 'OperationDefinition', undefined],
        ['leave', 'Document', undefined],
      ]);
    });
  });
});