target es2015 throw on circular dependency: Uncaught ReferenceError component is not defined

[elvisbegovic]

🐞 Bug report

at runtime

Is this a regression?

Yes, was working (target:es5) before targetting to es2015 by default

Description

A clear and concise description of the problem...

🔬 Minimal Reproduction

ng serve with tsconfig.json targetting es2015 throw :
Uncaught ReferenceError: ParentComponent is not defined

1. In ParentComponent I have @ViewChild(ChildComponent)

2. On ChildComponent's constructor I have
   constructor( @Inject(forwardRef(() => ParentComponent)) private parent:ParentComponent)

Target es5 everything is ok!

N.B. If you remove circular dependencies types
or in constructor (:ParentComponent) or in viewchild (:ChildComponent)
it works!

1. Download ap.zip
2. npm i && ng s
3. open localhost:4200

🔥 Exception or Error

child.component.ts:9 Uncaught ReferenceError: ParentComponent is not defined
    at Module.ParentComponent (child.component.ts:9)
    at Module../src/app/child.component.ts (child.component.ts:10)
    at __webpack_require__ (bootstrap:78)
    at Module../src/app/parent.component.ts (child.component.ts:9)
    at __webpack_require__ (bootstrap:78)
    at Module../src/app/app.module.ts (app.component.ts:24)
    at __webpack_require__ (bootstrap:78)
    at Module../src/main.ts (main.ts:1)
    at __webpack_require__ (bootstrap:78)
    at Object.2 (main.ts:12)

🌍 Your Environment

Angular CLI: 8.0.0-beta.16
Node: 11.12.0
OS: win32 x64
Angular: 8.0.0-beta.13
... animations, common, compiler, compiler-cli, core, forms
... language-service, platform-browser, platform-browser-dynamic
... router

Package                           Version
-----------------------------------------------------------
@angular-devkit/architect         0.800.0-beta.16
@angular-devkit/build-angular     0.800.0-beta.16
@angular-devkit/build-optimizer   0.800.0-beta.16
@angular-devkit/build-webpack     0.800.0-beta.16
@angular-devkit/core              8.0.0-beta.16
@angular-devkit/schematics        8.0.0-beta.16
@angular/cli                      8.0.0-beta.16
@ngtools/webpack                  8.0.0-beta.16
@schematics/angular               8.0.0-beta.16
@schematics/update                0.800.0-beta.16
rxjs                              6.4.0
typescript                        3.4.4
webpack                           4.30.0

cc @filipesilva

[filipesilva]

Still trying to figure out what's happening here. Looked at it a bit today and added a github repro at https://github.com/filipesilva/es2015-forwardref.

I see a different error though:

child.component.ts:78 Uncaught ReferenceError: Cannot access 'ParentComponent' before initialization
    at Module.ParentComponent (child.component.ts:78)
    at Module../src/app/child.component.ts (child.component.ts:10)
    at __webpack_require__ (bootstrap:78)
    at Module../src/app/parent.component.ts (child.component.ts:78)
    at __webpack_require__ (bootstrap:78)
    at Module../src/app/app.module.ts (app.component.ts:27)
    at __webpack_require__ (bootstrap:78)
    at Module../src/main.ts (main.ts:1)
    at __webpack_require__ (bootstrap:78)
    at Object.2 (main.ts:12)

I tried checking if the usage of Angular's es2015 bundles had anything to do with it. We automatically use those when "target": "es2015", is the tsconfig. But I saw the same error with es5 and es2015 bundles.

It seems to be related to the app code itself, and the result when transpiled to es5 vs es2015.

Still not sure of why though.

[filipesilva]

It's interesting to see what happens when ng serve --source-map=false is used though.

The error shows up as:

main.js:9644 Uncaught ReferenceError: Cannot access 'ParentComponent' before initialization
    at Module.ParentComponent (main.js:9644)
    at Module../src/app/child.component.ts (main.js:9576)
    at __webpack_require__ (runtime.js:79)
    at Module../src/app/parent.component.ts (main.js:9647)
    at __webpack_require__ (runtime.js:79)
    at Module../src/app/app.module.ts (main.js:9520)
    at __webpack_require__ (runtime.js:79)
    at Module../src/main.ts (main.js:9766)
    at __webpack_require__ (runtime.js:79)
    at Object.2 (main.js:9790)

Where (main.js:9644) is

/* harmony export (binding) */ __webpack_require__.d(__webpack_exports__, "ParentComponent", function() { return ParentComponent; });

Which belongs to the rest of the parent component code:

/***/ (function(module, __webpack_exports__, __webpack_require__) {

"use strict";
__webpack_require__.r(__webpack_exports__);
/* harmony export (binding) */ __webpack_require__.d(__webpack_exports__, "ParentComponent", function() { return ParentComponent; });
/* harmony import */ var tslib__WEBPACK_IMPORTED_MODULE_0__ = __webpack_require__(/*! tslib */ "./node_modules/tslib/tslib.es6.js");
/* harmony import */ var _angular_core__WEBPACK_IMPORTED_MODULE_1__ = __webpack_require__(/*! @angular/core */ "./node_modules/@angular/core/fesm2015/core.js");
/* harmony import */ var _child_component__WEBPACK_IMPORTED_MODULE_2__ = __webpack_require__(/*! ./child.component */ "./src/app/child.component.ts");



let ParentComponent = class ParentComponent {
    constructor() {
        this.child = null;
    }
};
tslib__WEBPACK_IMPORTED_MODULE_0__["__decorate"]([
    Object(_angular_core__WEBPACK_IMPORTED_MODULE_1__["ViewChild"])(_child_component__WEBPACK_IMPORTED_MODULE_2__["ChildComponent"]),
    tslib__WEBPACK_IMPORTED_MODULE_0__["__metadata"]("design:type", _child_component__WEBPACK_IMPORTED_MODULE_2__["ChildComponent"])
], ParentComponent.prototype, "child", void 0);
ParentComponent = tslib__WEBPACK_IMPORTED_MODULE_0__["__decorate"]([
    Object(_angular_core__WEBPACK_IMPORTED_MODULE_1__["Component"])({
        selector: 'app-parent',
        template: `<app-child #thisworks></app-child>`
    })
], ParentComponent);

So this is interesting. It errors out because ParentComponent is declared as

let ParentComponent = class ParentComponent {

But there's an export at the top using the let before it's declared. That kinda looks like a bug in Webpack.

[filipesilva]

I've made a simple reproduction and bug report on Webpack: webpack/webpack#9060

This issue is now blocked on a fix there.

[filipesilva]

This issue was not caused by a Webpack bug but rather a problem between forwardRef and constructor types when targetting ES2015. I have detailed the problem in angular/angular#30106.

A temporary workaround is to remove the type in the constructor parameter for ChildComponent:

// Instead of 
export class ChildComponent {
  constructor(@Inject(forwardRef(() => ParentComponent)) private parent: ParentComponent) { }
}

// Use
export class ChildComponent {
  private parent: ParentComponent;
  constructor(@Inject(forwardRef(() => ParentComponent)) parent) { 
    this.parent = parent as ParentComponent;
  }
}

I'm closing the issue here because it really should be addressed in the framework repository instead via angular/angular#30106, because it's not a CLI issue but a forwardRef design/usage issue.