Force message in matchers to always be a function (jestjs#3972)

* Force message in matchers to always be a function

* Rename variable back to message instead of messageFn

packages/jest-matchers/src/__tests__/extend.test.js

@@ -16,8 +16,8 @@ jestExpect.extend({
  toBeDivisibleBy(actual, expected) {
  const pass = actual % expected === 0;
  const message = pass
- ? `expected ${actual} not to be divisible by ${expected}`
- : `expected ${actual} to be divisible by ${expected}`;
+ ? () => `expected ${actual} not to be divisible by ${expected}`
+ : () => `expected ${actual} to be divisible by ${expected}`;
 
  return {message, pass};
  },
@@ -38,8 +38,8 @@ it('exposes matcherUtils in context', () => {
  _shouldNotError(actual, expected) {
  const pass = this.utils === matcherUtils;
  const message = pass
- ? `expected this.utils to be defined in an extend call`
- : `expected this.utils not to be defined in an extend call`;
+ ? () => `expected this.utils to be defined in an extend call`
+ : () => `expected this.utils not to be defined in an extend call`;
 
  return {message, pass};
  },

packages/jest-matchers/src/index.js

@@ -99,18 +99,10 @@ const expect = (actual: any): ExpectationObject => {
 };
 
 const getMessage = message => {
- // for performance reasons some of the messages are evaluated
- // lazily
- if (typeof message === 'function') {
- message = message();
- }
-
- if (!message) {
- message = utils.RECEIVED_COLOR(
- 'No message was specified for this matcher.',
- );
- }
- return message;
+ return (
+ (message && message()) ||
+ utils.RECEIVED_COLOR('No message was specified for this matcher.')
+ );
 };
 
 const makeResolveMatcher = (

packages/jest-matchers/src/matchers.js

@@ -543,7 +543,8 @@ const matchers: MatchersObject = {
  const traversedPath = result.traversedPath.join('.');
 
  const message = pass
- ? matcherHint('.not.toHaveProperty', 'object', 'path', {
+ ? () =>
+ matcherHint('.not.toHaveProperty', 'object', 'path', {
  secondArgument: valuePassed ? 'value' : null,
  }) +
  '\n\n' +
@@ -552,7 +553,8 @@ const matchers: MatchersObject = {
  `Not to have a nested property:\n` +
  ` ${printExpected(keyPath)}\n` +
  (valuePassed ? `With a value of:\n ${printExpected(value)}\n` : '')
- : matcherHint('.toHaveProperty', 'object', 'path', {
+ : () =>
+ matcherHint('.toHaveProperty', 'object', 'path', {
  secondArgument: valuePassed ? 'value' : null,
  }) +
  '\n\n' +

types/Matchers.js

@@ -13,7 +13,7 @@ import type {SnapshotState} from 'jest-snapshot';
 
 export type ExpectationResult = {
  pass: boolean,
- message: string | (() => string),
+ message: () => string,
 };
 
 export type RawMatcherFn = (