[babel-jest] Failures on decorators with async methods

[julien-f]

Do you want to request a feature or report a bug?

Bug

What is the current behavior?

Syntax error when using decorators on async methods:

$ jest index.spec.js
 FAIL  ./index.spec.js
  ● Test suite failed to run

    index.spec.js:6
        bar() {}}, (_applyDecoratedDescriptor(_class.prototype, "bar", [foo], Object.getOwnPropertyDescriptor(_class.prototype, "bar"), _class.prototype)), _class);
        ^^^

    SyntaxError: Unexpected identifier

      at ScriptTransformer._transformAndBuildScript (node_modules/jest-runtime/build/script_transformer.js:318:17)

Test Suites: 1 failed, 1 total
Tests:       0 total
Snapshots:   0 total
Time:        0.459s
Ran all test suites.

Repro repo: https://github.com/julien-f/issue-babel-jest-decorators-async-methods

What is the expected behavior?

Should compile and work as if it were previously processed by @babel/cli.

[modosc]

we're seeing this too. i wonder if this has anything to do with jest-runtime pulling in babel-core ^6.0.0?

[modosc]

this seems to go away if we use @babel/plugin-transform-async-to-generator even though that shouldn't be necessary with our current node version (8.9)

[SimenB]

Hah, this is weird. You've found a bug in Babel caused by our use of retainLines: https://github.com/facebook/jest/blob/c243f67efbae70bd416a61b0c899485bde3a702b/packages/babel-jest/src/index.js#L72

Using that option produces the following output (reusing your example repo):

$ yarn --silent babel --retain-lines index.spec.js
warning package.json: No license field
function _applyDecoratedDescriptor(target, property, decorators, descriptor, context) {var desc = {};Object['ke' + 'ys'](descriptor).forEach(function (key) {desc[key] = descriptor[key];});desc.enumerable = !!desc.enumerable;desc.configurable = !!desc.configurable;if ('value' in desc || desc.initializer) {desc.writable = true;}desc = decorators.slice().reverse().reduce(function (desc, decorator) {return decorator(target, property, desc) || desc;}, desc);if (context && desc.initializer !== void 0) {desc.value = desc.initializer ? desc.initializer.call(context) : void 0;desc.initializer = undefined;}if (desc.initializer === void 0) {Object['define' + 'Property'](target, property, desc);desc = null;}return desc;}it('supports decorators on async methods', () => {var _class;
  const foo = () => {};let

  C = (_class = class C {
    async
    bar() {}}, (_applyDecoratedDescriptor(_class.prototype, "bar", [foo], Object.getOwnPropertyDescriptor(_class.prototype, "bar"), _class.prototype)), _class);

});

async
bar() {}

is not valid JS.

$ yarn --silent babel --retain-lines index.spec.js | node
warning package.json: No license field
[stdin]:6
    bar() {}}, (_applyDecoratedDescriptor(_class.prototype, "bar", [foo], Object.getOwnPropertyDescriptor(_class.prototype, "bar"), _class.prototype)), _class);
    ^^^

SyntaxError: Unexpected identifier
    at createScript (vm.js:80:10)
    at Object.runInThisContext (vm.js:139:10)
    at Object.<anonymous> ([stdin]-wrapper:6:22)
    at Module._compile (module.js:643:30)
    at evalScript (bootstrap_node.js:462:27)
    at Socket.<anonymous> (bootstrap_node.js:233:15)
    at emitNone (events.js:111:20)
    at Socket.emit (events.js:208:7)
    at endReadableNT (_stream_readable.js:1055:12)
    at _combinedTickCallback (internal/process/next_tick.js:138:11)

For comparison, without --retain-lines:

function _applyDecoratedDescriptor(target, property, decorators, descriptor, context) { var desc = {}; Object['ke' + 'ys'](descriptor).forEach(function (key) { desc[key] = descriptor[key]; }); desc.enumerable = !!desc.enumerable; desc.configurable = !!desc.configurable; if ('value' in desc || desc.initializer) { desc.writable = true; } desc = decorators.slice().reverse().reduce(function (desc, decorator) { return decorator(target, property, desc) || desc; }, desc); if (context && desc.initializer !== void 0) { desc.value = desc.initializer ? desc.initializer.call(context) : void 0; desc.initializer = undefined; } if (desc.initializer === void 0) { Object['define' + 'Property'](target, property, desc); desc = null; } return desc; }

it('supports decorators on async methods', () => {
  var _class;

  const foo = () => {};

  let C = (_class = class C {
    async bar() {}

  }, (_applyDecoratedDescriptor(_class.prototype, "bar", [foo], Object.getOwnPropertyDescriptor(_class.prototype, "bar"), _class.prototype)), _class);
});

@julien-f Can you open up an issue with Babel? This is a bug with either retainLines or the transform.

@cpojer thoughts on dropping the retainLines on our side? We ask babel to give us sourcemaps, so it doesn't really provide much value in babel-jest, does it?

@modosc Not related to jest-runtime version, as we support babel 7 in babel-jest. And using the extra transform works as the async keyword causing the syntax error is compiled away.

[modosc]

the fix was reverted here and as of [email protected] the problem is back, can you reopen this please?

[SimenB]

After merging #5177, we should be OK to remove it again.

[SimenB]

See #5594

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